Info-Mac 4/Info_Mac IV CD-ROM (Pacific HiTech Inc.)(August 1994).iso/Applications/EVDesign 1.1/MiscInfo/Heaters.Txt

Text File | 1994-05-20 | 37KB | 745 lines

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Miscellaneous heater info gleaned from the EV mailing list on the Internet.
You'll note from the dates that this was a cold weather thread. These show
that there are a lot of different ways to successfully heat your EV in some
really cold climates.
Thanks to all who contribute to the EV mailing list!

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Date: Tue, 2 Nov 1993 09:54:45 -0600
From: David Luneau <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: EV heating

I will assume this question is for me -- I wish I knew how some of you
break a message apart and put your answers under the appropriate question.

I did the Rabbit conversion from a kit from ElectroAutomotive (408-429-1989).
I did it myself with some neighbor-type help  -- 170 hours of my labor, but
I am not much of a mechanic.

No regen braking.  The only flywheel is the original one that is used to
interface the clutch and original transmission to the Advanced DC motor.
I thought I read somewhere that the motor was a 9 inch, but I measured the
other day and it was 8 inches in diameter.  However, the Solar Electric
catalog lists both the 8 in. and 9 in. motors as 8 inches in diameter (typo?).
So, I think the motor I have is the 8 inch motor.

The performance is fine for my use.  I get about 50-55 miles range in the
summer and about 40 miles when it turns cold.  I have Trojan T-105 batteries
(16 of them in series).  I wish I had gotten the T-125s, same size but more
capacity (and weight).  I will have had it on the road for a year on Nov.14
and will have put 9500 miles on it in that time.  Better batteries next time
and better tires (when these wear out) and I hope my range will increase to
60-70 miles.

Hope this helps you.

David

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Date: Tue, 4 Jan 1994 22:13:51 PST
From: Randy A. Holmquist <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: More on EV heaters

>
>Driving an EV in the mild West Coast Canadian winters has been
>quite comfortable using a standard 120 volt AC ceramic heater element
>in place of the old water-heated heater core.
>
>It seems, though, that below-freezing weather is a little much
>for these heaters to handle. (coat time :-). Power consumption
>is 8-15 amps...not much when you consider level cruising is eating
>up 100-125 amps.
I have installed this same heater core in 3 of my EV conversions.
The only complaint was when I mistakenly installed a 10 amp fuse
in the heater circuit instead of a 20 .
After about a month the owner very politely said he
was not to happy with the amount of heat for defrost.
A quick fuse change and he's a happy EVr.
Espar makes a 6000 btu diesel furnace for boats and truck cabs.
I used one for a while but felt like a traitor ( a very warm traitor ).
Electric heat is instant !!
###

--
Randy Holmquist
Lightning Electric Vehicles
[e-mail]
The ICE age is over

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Date: Tue, 4 Jan 1994 09:55:57 -0800
From: Robert Weeks <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: AC/heater data

> How much enegry (horse power or KW) does it take to run an A/C unit or heater?

There was a lot of discussion about this recently in the USENET
sci.energy newsgroup.  I didn't save any of the posts but you might be
able to find it archived somewhere. :)

I was looking through a brochure from Siemens Automotive and found some
data on one of their heating/air conditioning systems for passenger cars.
The brochure quoted a heating capacity of 8.7 kW for an outside
temperature of -20 deg C and a heater air throughput of 80 l/s.  The
brochure gave two cooling capacities (dry and wet).  The dry cooling
capacity was 4.7 kW for an outside temperature of 40 deg C, an air flow
rate of 130 l/s and a relative humidity less than 15%.  The "wet" cooling
capacity was 6.9 kW for an outside temperature of 40 deg C, an air flow
rate of 120 l/s and a relative humidity of approximately 40%.

The data above were for a combined heat/AC unit. The Siemens brochure
also gave specs on a heater without AC.  For this unit the heating
capacity was 10.1 kW for an outside temperature of -10 deg C and a water
throughput of 400 l/h.

The actual amount of power drawn from an EV's batteries would be
dependent on the efficiency of the heating/AC unit, but these numbers
should give you some idea of the power required for typical passenger cars.

Hope this helps.

--
Robert Weeks
[e-mail]

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Date: Tue, 4 Jan 1994 19:59:07 PST
From: Peter Jacobs <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: More on EV heaters

Going back over previous months EVLOGS, there seems to have been
quite a bit of discussion on heaters in Oct. 93. I can't believe
my eyes when I read about heating being a major stumbling block
to the introduction of electric vehicles.

Driving an EV in the mild West Coast Canadian winters has been
quite comfortable using a standard 120 volt AC ceramic heater element
in place of the old water-heated heater core.

It seems, though, that below-freezing weather is a little much
for these heaters to handle. (coat time :-). Power consumption
is 8-15 amps...not much when you consider level cruising is eating
up 100-125 amps.

Like most things EV ,the solution lies in tightening up serveral small
inefficient areas to make the heating system workable.
Some suggestions are:
        -improve insulation in the passenger compartment.
        -run a small heater, on a timer, while charging.
        -when driving, use the air re-circulation setting as much
         as possible.
        -and, when all else fails, lower ones expectations.

Pre-heating the cab for 15 minutes before departure in below
freezing weather is most effective. A 1500 Watt portable baseboard
heater does an admirable job. In fact, when I use my ICE vehicle,
the lack of heat for the first few minutes is annoying.

I guess the point I'm trying to make is that if a back-yard mechanic
can come up with an acceptable heater solution, certainly the engineers
in Detroit can too, even for severe winter climates.

--
Peter Jacobs
[e-mail]

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Date: Wed, 5 Jan 1994 15:31:50 -0500
From: Jeff A. Kester <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: EV heaters

William A Segraves <[e-mail]>  wrote:
>
> [propane stuff snipped]
>
> The above doesn't seem to be as cost-effective as the small ceramic heaters
> such as Peter Jacobs suggested, and I believe, used in his S-10 conversion.
> I'm looking at a 12 VDC, 300 Watt unit in Northern's Winter catalog # 72,
> Item # 331631, $49.99, phone [phone].
>

The problem I've found with trying to supply cabin heat (especially wind-
screen defrosting at high mph) via a 12 volt unit, is the large amps required
to get any significant heat.  As a vehicle builder, I've tried to isolate
the 12v car systems from the 96-120v drive systems when ever possible.
I don't like the idea of having a lot of high-voltage/high-amperage DC
wiring in the passenger compartment because of the possibility of the
vehicle occupants getting zapped in an accident.  However, unless I
want to load the vehicle with 12v deep-cycle batteries for heater use,
there's not much choice.

A 12v heater trying to heat a compact car cabin is going to need to be
rated at least a 1000w to do any good.  Call it an 80 amp draw.  Most
DC/DC convertors are rated in the 25-30 amp range so they're going to
start smokin'.  A 12v deep-cycle lead-acid would last about an hour and
a half (assuming nothing else was on) and we'd have a frozen New Yorker
again.

The most pratical solution to heating a converted EV seems to be the
high voltage ceramic element.  These heaters are fairly inexpensive
($125 from Solar Car Corp., includes control relay) and provide about
1000 watts per unit.  As I'm sure Peter will attest, installation is
no biggie and the 10a max. draw is insignificant in regard to vehicle
range.  The advantage of these units over a fuel-fired heater is in the
installation.  The ceramic element can be mounted on an Aluminum or
plastic plate and put in place of the vehicles' heater core.  The ducting
for heating and defrosting is already there and the original distribution
controls will function nicely.  I install a micro-switch on the temp. lever
to activate the heat control relay and heat output is determined by
airflow from the 12v blower.  (I actually install two heaters and two
micro-switches: one switch kicks on one heater at 1/2 way on the temp.
lever, the other switch kicks on the other heater at full.)  Supply
wiring is brought into the heater plenum through the old heater hose
grommets in the firewall.  (Of course, if you have a VW Beetle with
a gaz heater already installed, that's even easier.)

There's also the Russco "Safety Electric Vehicle Heater" which replaces the
ICE as a source of hot liquid for the heater core.  The 2000 watt model re-
quires 16.7 amps@120v with control power of 1.6 amps@12v.  It's basically
a mini hot water heater and 12v pump that you plumb into the heater core.
It's rather bulky (4"x8"x16"), weighs a little over 6 lbs. and requires
a coolant reservior as well.  I'd rather get as many liquids out of the
vehicle as possible so my vote's still with the ceramic.  The Russco
heater costs about $400. (You've probably seen their ads in _Current
EVents_.)

        ----------------------------------------------------------------
        | Jeff Kester                  | "The only time I open my      |
        | Product Development          |  mouth is when I have to      |
        | GreenWheels Electric Car Co. |  change feet."                |
        | 181 Elliott St., #605        |                               |
        | Beverly, MA 01915  USA       | Internet:                     |
        | Voice: [phone]        | [e-mail] |
        ----------------------------------------------------------------

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Date: Wed, 5 Jan 1994 20:43:32 PST
From: Randy A. Holmquist <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: Heaters again

>BTW, ceramic heaters apparently are very safe.  Mine was stuck on for
>about a week when I first installed it (I DID wonder where all the extra
>heat was coming from), and the plastic plenum that the heater is screwed
>onto didn't suffer at all.  It was on because I used an undersized relay.
>The relay had a high enough current rating, but it was not capable of
>breaking 96V DC.  It was rated at 120V AC, but I failed to read the next
>line on the data sheet which said "or 28V DC".  A DC voltage is harder to
>break than an AC voltage.  I don't know the ratings on the Ford starter
>solenoid I am using, but I figured if it could handle 100s of amps to a
>starter, it could handle the 10A to my heater.  There is the issue on
>solenoids of "continuous" vs. "intermittent" use, but I figured some
>people with Fords crank their engines for 10 or 15 minutes at a time, and
Your Ford starter relay should be replaced with one rated 120 VDC.
I ran a continuas duty dual battery solenoid 60amp\ 12v for almost a year
but it did die. All my conversions now use a 120vdc rated solenoid.
It is worth the piece of mind.
You should also not be using the high /low switch from the ac heater .
Just wire the ceramic element direct to the relay.
I run the ground side of the relay through a red lit switch,
and the positive through the fan switch as you did.
The 120vdc comes from the controller side of the main contactor
so when the ignition is off so is the heater.
randy
###

--
Randy Holmquist
Lightning Electric Vehicles
[e-mail]
The ICE age is over

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Date: Wed, 5 Jan 1994 16:40:27 -0600
From: David Luneau <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Heaters again

Jeff Kester posted the following:

> The most pratical solution to heating a converted EV seems to be the
> high voltage ceramic element.  These heaters are fairly inexpensive
> ($125 from Solar Car Corp., includes control relay) and provide about
> 1000 watts per unit.  As I'm sure Peter will attest, installation is
> no biggie and the 10a max. draw is insignificant in regard to vehicle
> range.  The advantage of these units over a fuel-fired heater is in the
> installation.  The ceramic element can be mounted on an Aluminum or
> plastic plate and put in place of the vehicles' heater core.  The ducting
> for heating and defrosting is already there and the original distribution
> controls will function nicely.  I install a micro-switch on the temp. lever
> to activate the heat control relay and heat output is determined by
> airflow from the 12v blower.  (I actually install two heaters and two
> micro-switches: one switch kicks on one heater at 1/2 way on the temp.
> lever, the other switch kicks on the other heater at full.)  Supply
> wiring is brought into the heater plenum through the old heater hose
> grommets in the firewall.  (Of course, if you have a VW Beetle with
> a gaz heater already installed, that's even easier.)

Jeff, this is almost exactly what I did on my Rabbit except:

1.  I paid <$40 at K-Mart for their cheapest 2 speed ceramic heater, set
    it on high, and removed the 120V AC fan.
2.  I paid $6 for a Ford starter solenoid for the control "relay".
3.  I took the "relay" control voltage from the blower fan wire.  This
    ensures that the fan must be on (as well as a toggle switch I added)
    for the heater to work.

The heater works fine but 2 (2000W) would be better than just 1 (1000W).
But the way my range drops in the winter anyway, I'm not sure I could
afford a second one.  We need a battery technology that is not such a
strong function of temperature.

BTW, ceramic heaters apparently are very safe.  Mine was stuck on for
about a week when I first installed it (I DID wonder where all the extra
heat was coming from), and the plastic plenum that the heater is screwed
onto didn't suffer at all.  It was on because I used an undersized relay.
The relay had a high enough current rating, but it was not capable of
breaking 96V DC.  It was rated at 120V AC, but I failed to read the next
line on the data sheet which said "or 28V DC".  A DC voltage is harder to
break than an AC voltage.  I don't know the ratings on the Ford starter
solenoid I am using, but I figured if it could handle 100s of amps to a
starter, it could handle the 10A to my heater.  There is the issue on
solenoids of "continuous" vs. "intermittent" use, but I figured some
people with Fords crank their engines for 10 or 15 minutes at a time, and
that is as long as I ever run my heater.

David Luneau

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Date: Wed, 5 Jan 1994 20:16:06 PST
From: Peter Jacobs <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: Heaters again

David Luneau says, in part,
>Jeff, this is almost exactly what I did on my Rabbit except:
>1.  I paid <$40 at K-Mart for their cheapest 2 speed ceramic heater, set
>    it on high, and removed the 120V AC fan.
>2.  I paid $6 for a Ford starter solenoid for the control "relay".
>3.  I took the "relay" control voltage from the blower fan wire.  This
>    ensures that the fan must be on (as well as a toggle switch I added)
>    for the heater to work.
>

I used a similar unit on the S-10, but removed the ceramic element
and installed it on an ABS plastic adaptor plate where the old heater
core was mounted. At first I made the wiring rather elaborate, with
3 levels of heat available, but after some use decided that
a) the ac switch was not very happy switching 120 volts dc, and
b) I always had the thing on high anyway.

So, while cleverly re-wiring the unit with it still mounted
in the heater plenum, a small slip with an uninsulated screwdriver
demonstrated the _awesome_ power of a 120 volt dc short circuit.

My head was stuffed up under the dash when the blinding flash,
brighter than any arc welder, went off. I withdrew rather quickly
with the only damage being a blackened face and arms, temporary
blindness, and a renewed healthy respect for electricity....not
to mention the cost of a new heating element.  My dad always
said "...you can't buy experience, but you sure have to pay
for it". I think I'm beginning to understand  :-)

So safety is a prime concern. But once the unit is properly mounted,
it should have a long trouble-free life.

The relay I first used was an RV dual battery relay. That didn't
last more than a month, so I bought an inexpensive 120 volt dc
relay from a local EV company which works well.

I like Jeff's idea mentioned earlier of having a second heating element
activated by the heat control cable. One could use the extra "boost"
in very cold weather, and on start ups.

Also, David's method of wiring to ensure the fan is running when
the element is "lit" is good. I did the same after discovering how
hot the plastic plenum gets when relying on un-aided air flow.

I guess the tinkering and improvements never stop. That's the fun
of EV'ing.

--
Peter Jacobs
[e-mail]
    Re: Heaters again                                                       %

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Date: Thu, 6 Jan 1994 13:19:01 -0500
From: Jeff A. Kester <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: Heaters

David Luneau writes:

> I only saw expensive ones in catalogs when I was looking.
> Please pass on any info regarding price and ordering, and I will buy the
> properly rated relay (as soon as mine fails or when I feel rich again).

 I found one buried in the Newark Electronics catalog that fits the bill
nicely. (I also use this relay for the timer controlled charger circuit.)

It's a Stancor 120 Series Heavy Duty DC Power Contactor which is "water
resistant and durable in high temperature and high vibration conditions.
Circuit: SPNO. Termination: #10-32 UNF-2A thread [for control wires, load
studs are 5/16-24]. Continuous duty types are rated 100A full load, 400A
inrush with silver alloy contacts.  Operating temperature range is -20F to
+120F..."

These relays are about 2"x3"x4" high and they have generous stud exposure
for adding multiple hook-ups.  They're available w/ std. braket (for flat
surface mounting) or an "L" bracket ("L" bkt is .30 more).  Coil voltages
range from 12-36vdc. 12v coil unit has coil res. of 16.0 ohms. Stancor part
No. (std. bkt) is 120-901, Newark stock No. is 50F3662. Cost $15.52 ea.

They've got branches worldwide, call the main office to find one at (312)
784-5100 (or call/e-mail me and I'll try to help)

----
>Good idea, but that thought didn't cross my mind until I had the plenum
>reinstalled.  You nearly have to (and ARE SUPPOSED TO) remove the dash in
>a Rabbit to remove the plenum.  It takes several hours of twisted-body,
>face-under-the-dash work, so once again, as long as it works...

 Did your wascally wabbit once have A/C?  The heater core should be
able to be gingerly extracted by removing the accelerator pedal, then
popping off a plastic cover on the side of the plenum which will expose the
heater core.  After that it just slides out.  Grab the Ohmmeter and you'll
soon see how to hook-up all those terminals on the ceramic to DC input.
(And yes, a ceramic can be obtained by gutting an AC heater assembly but
that's rather wasteful.  I'm trying to find the manufacturer of these things
so's I can buy/sell direct.  If we can buy the whole heater for under $50,
the element can't be worth much.)

----
> Doesn't that mean that when your foot is off the accelerator and the main
> contactor is open that the heater is off, too?  It would on my car.  The
> power to my heater comes directly from the batteries, which is bad if your
> relay arc welds itself shut (I watched it happen, Peter, but it was less
> violent than your experience).

 Gads! That means you've only got one contactor for high voltage cut-out!
Put in two so when one arc welds shut you still have a method of shutting
off your new arc-welder-on-wheels.  Not cheap but a definate minimum for
safety.
----

>...I get recirculated air when the switch is in the HEAT position.  This
> makes the heater work much better.  When the windshield fogs, I have to
> momentarily switch to DEFROST position, which also switches back to
> outside air.

 Well, since you've already been daring and fiddled with vac lines, re-plumb
the "flap housing" valve (the one under the hood, blue vac line) so it's
only activated when in the "vent" position.  A little experimentation with
the 5-way distribution valve should point the way (I don't have one handy-
-sorry).
----
Good Luck!

        ----------------------------------------------------------------
        | Jeff Kester                  | "The only time I open my      |
        | Product Development          |  mouth is when I have to      |
        | GreenWheels Electric Car Co. |  change feet."                |
        | 181 Elliott St., #605        |                               |
        | Beverly, MA 01915  USA       | Internet:                     |
        | Voice: [phone]        | [e-mail] |
        ----------------------------------------------------------------

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Date: Sun, 9 Jan 1994 17:47:45 -0500
From: Jeff A. Kester <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: Heaters & Contactors

Otmar Ebenhoech <[e-mail]> writes (in reference to my recommendation
of the Stancor contactor):

> I looked this one up because it sounded so good. I have doubts about this
> relays ability to extinguish 120V arcs. It has no magnetic blowouts and is
> only rated at 36V. It might be worth a call to the factory to find if they
> have a electrical life rating for 120 VDC use with a inductive load.

        You may be right.  The catalog listing doesn't give a contact
voltage rating.  The 36vdc IS listed as one of the voltages availble for
the coil.  I talked to Stancor before purchasing these units and I seem to
recall them saying the relays were suitable for 120vdc loads @ 100A.  (It
was awhile ago. Besides even if it is only 36vdc at the contacts, the 100A
full load, 400A inrush would be more than adequate for heater loads.)

He also recommends the following:

> I use a RL9101 from C&H electronics [phone]. 120 VDC rated at 20 A.
> Coil is 12V. It's open frame so needs a cover. It has a built in magnetic
> blow out. This is a potter & Brumfield #PRD-JDJO-12.

        Newark sells covers for the PRD series relays.  They also have
listings for the Potter & Brumfield T91 series relays (they weren't
available when I bought the Stancors--thanks for reminding me).  The T91E
series are rated at 150vdc, 30A and they've got magnetic blow-outs.  The
good news is they're only $7.05 each, the bad news is they're PC board
mount.  Either way, call Potter & Brumfield, they're very helpful.  If
you can't buy direct, most electronics catalog suppliers will get you what
you need if you've got the P & B numbers.

> Digikey used to sell a (Heater for hot wind air) PTC thermistor. Two types
> - 680W and 740W. The new catalogs don't have it anymore but I found it in
> #925 on page 167. Unfortunatly #925 is sep-oct 1992. The Thomas register
> might be a good place to check for mfg. Good Luck!

        I know of a thermistor grid that Panasonic used to make, unfortunately
it's NLA.  I'm plowing through the Thomas registers now--I'll post results
ASAP.

> One contactor is plenty in my book if you have a semiconductor fuse. [...]
>                                    ^^^^^^^^^^^^^^              ^^^^^
> Peter Jacobs writes:
> >There seem to be 2 schools of thought on the correct method
> >of activating the main contactor:
> >
> >       -throttle pedal activated
> >       -ignition switch activated
>
> Count my vote for ignition switch activated.

        The 1 or 2 contactor choice is pretty much up to individual.  I use
two.  The click-clunk factor isn't a big deal to me.  (I can hear you now,
it must be cuz I'm already nuts... 8^) )  I find it's easier install
additional safety lock-out circuits with two contactors.  We install
them on the key activated contactor so if all conditions are not correct,
i.e. hood closed, battery boxes closed and latched, vent fans operating and
charge cord stowed on-board, a dashboard indicator lights and the vehicle
will not operate.  The other contactor only closes when romping the pedal, so
even if the key is on, there still isn't a complete circuit to the controller.
It won't close if the key isn't on.  Either way Otmar's right--a contactor
AND fuse are the minimum for protection.

        ----------------------------------------------------------------
        | Jeff Kester                  | "The only time I open my      |
        | Product Development          |  mouth is when I have to      |
        | GreenWheels Electric Car Co. |  change feet."                |
        | 181 Elliott St., #605        |                               |
        | Beverly, MA 01915  USA       | Internet:                     |
        | Voice: [phone]        | [e-mail] |
        ----------------------------------------------------------------

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Date: Mon, 10 Jan 1994 00:41:03 -0800
From: Otmar Ebenhoech <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Heaters and contactors

>Otmar writes:
>>It's also a good idea to put a freewheel diode on the heater core to reduce
>>the inductive spike (and arc) on turn off.
>
>Could you elaborate a bit on this please, Otmar? It sounds like I need one.
>(I'm using the Potter Brumfield 120 volt relay already.)

Peter, I'm not sure of the intensity of the inductive effect on the heater
cores which we are using. I only know from experience that they can draw a
pretty long arc when breaking the connection.
        When a the circuit to an inductive load is suddenly broken, the
magnetic field around the wires/coils collapses and causes a high voltage
spike. This spike tries to keep current flowing in the same direction that
it was going before the circuit was broken. A diode placed in reverse
across the inductive load will redirect this current spike back into the
load until it has subsided. Therefore it reduces the arcing on the
contactor.
        For the heater cores I would try a 6 amp or larger diode, 200 volt
minimum, available at radio shack. This would then be placed in parallel
with the heater core with the annode on negative and the cathode on the
positive side. The end with the white line connects to the positive
terminal. If you get it backwards you'll blow your fuse. (you do have one I
hope).

>I have a fusable link in the battery line (in a small box under the hood)
>and a Heinemann breaker under the dash for a safety disconnect,
>but no fuse in or between  battery packs. My concern was that the
>blowing fuse might spark a battery explosion.
>Would a KAA-400 fuse be safe to install in the battery boxes?

        I install them in battery boxes though a can't guarantee that that
is really the best thing to do. The KAA type fuses seem to be well sealed
and I have never seen the mechanical structure comprimised when blown. I
like the fact that the fuse is structurally strong and needs no fuse
holder. I usually just connect one end on a battery and the other on a
cable.
        I avoid those fusible links with a passion. They melt. They spark.
And if your controller blows with one of those it's a lot harder to repair.
Replacing melted PC board traces is much harder than just swaping Fets.
        Placing fuses is always difficult. You need to figure where you're
most likely to need them. There will allways be unfused areas in the
individual battery packs. The key in my eyes is to fuse the circuit with
the highest voltage in the smallest area. (the place where a wrench would
most likely fall) Then insulate all your tools and try to avoid vaporizing
battery terminals.
   -----------------------------------------------------------------------
     Otmar Ebenhoech         The Electric Speed Shop     [e-mail]
   -----------------------------------------------------------------------

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Date: Fri, 7 Jan 1994 10:16:00 GMT
From: Paul Compton <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Re: Heaters

        My EV (currently being re-cycled into a new vehicle) had had the
entire heater/de-mister removed, this meant I could not even blow cold
air onto the screen (a chamois leather was an esential driving accesory)
after getting fed up of this I came up with the following solution.
        I used a length of aluminium channel with a pair of insulating
blocks fitted at each end which held the channel just clear of the screen
a length of constantan wire was stretched between these blocks and run at
red heat, it is necesarry to position a piece of foil on the screen to
avoid local overheating. Total consumption was about 50W but the channel
being so close to the screen (bent to a similar curvature) meant that
de-frosting (from -15 C ) was accomplished in approx 2 min.

                Paul Compton

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Date: Fri, 7 Jan 1994 11:11:16 -0800
From: Otmar Ebenhoech <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Heaters and contactors

Jeff Kester writes:
> I found one buried in the Newark Electronics catalog that fits the bill
>nicely. (I also use this relay for the timer controlled charger circuit.)

I looked this one up because it sounded so good. I have doubts about this
relays ability to extinguish 120V arcs. It has no magnetic blowouts and is
only rated at 36V. It might be worth a call to the factory to find if they
have a electrical life rating for 120 VDC use with a inductive load.

I use a RL9101 from C&H electronics [phone]. 120 VDC rated at 20 A.
Coil is 12V. It's open frame so needs a cover. It has a built in magnetic
blow out. This is a potter & Brumfield #PRD-JDJO-12.

It's also a good idea to put a freewheel diode on the heater core to reduce
the inductive spike (and arc) on turn off.

>> (And yes, a ceramic can be obtained by gutting an AC heater assembly but
>> that's rather wasteful.  I'm trying to find the manufacturer of these things
>> so's I can buy/sell direct.  If we can buy the whole heater for under $50,
>> the element can't be worth much.)

Digikey used to sell a (Heater for hot wind air) PTC thermistor. Two types
- 680W and 740W. The new catalogs don't have it anymore but I found it in
#925 on page 167. Unfortunatly #925 is sep-oct 1992. The Thomas register
might be a good place to check for mfg. Good Luck!



> Gads! That means you've only got one contactor for high voltage cut-out!
>Put in two so when one arc welds shut you still have a method of shutting
>off your new arc-welder-on-wheels.  Not cheap but a definate minimum for
>safety.

Pleeeese, Quit the theatrics. One contactor is plenty in my book if you
have a semiconductor fuse. True, the controllers fail in full on position
but a KAA style fuse will disconnect in 1/10 of a second. I've blown
several controllers and never had more than a quick lurch before the fuse
blew.

Peter Jacobs writes:
>There seem to be 2 schools of thought on the correct method
>of activating the main contactor:
>
>        -throttle pedal activated
>        -ignition switch activated

Count my vote for ignition switch activated.
Reasons:
1 I hate the noise.
2 Controllers ramp down in 3/4 of a second and contactors switch in .2
seconds so it might be possible to break the contactor under load by
pulling your foot off the accelerator very quickly.



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     Otmar Ebenhoech         The Electric Speed Shop     [e-mail]
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Date: Mon, 10 Jan 1994 11:21:21 -0800
From: Otmar Ebenhoech <[e-mail]>
To: Multiple recipients of list EV <[e-mail]>
Subject: Heaters and fuses

David Coale writes:
>Just a note from a novice EVer concerning the tech talk. The response
>below could be a little more complete for my level of knowledge.
>
>>        For the heater cores I would try a 6 amp or larger diode, 200 volt
>>minimum, available at radio shack. This would then be placed in parallel
>>with the heater core with the annode on negative and the cathode on the
>>positive side. The end with the white line connects to the positive
>>terminal. If you get it backwards you'll blow your fuse. (you do have one I
>>hope).
>
>The diode mentioned above is for the coil of the relay to the heater element
>and not the element it's self(?). If this is correct then the fuse you mention
>is for the relay coil(?) or the heater.  I think I need some straightening out
>here.
>
>also your comments on fuses and fusing for accessories and gauges (diode
>protection), would be appreciated.

The diode mentioned is for the heater core itself not for the relay coil at
all (though all relays should have a similar diode across their coils.)
The diode mentioned could be mounted right on the heating element accross
the two wires that supply power to the core. This is well after the relay
and just snubbs the spike caused by the termination of current flow in the
heater core.
I'm sorry if this wasn't clear, I have a little trouble explaining it
without scratch paper. Please ask me more questions if you don't
understand.

        My preferences for fusing accesories and guages is as follows: I
use 30 amp blade types for the heater core. (not rated for the voltage so
they will melt into the holder in case of a dead short. :-(   There are
better fuses available but I havn't found any holders I like.)
        Guages I fuse with 4 amp because the smaller ones have enough
voltage drop to skew the ammeter readings. Usually I end up with a bunch of
inline fuse holders though I don't like their relative suceptibility to
corrosion. I try to wire all connectors with positive polarity locks so
they can only be reconnected correctly. This saves on blown ammeters.
Generally I use autoomotive trailer plugs which come in 2 through 8
connectors and can be cut with a knofe for custom configurations.  Bob
Schneevies usually puts two diodes in opposite directions across ammeters
to reduce the maximum voltage at the guage and I think this is a good idea.
When two diodes are across the ammeter the maximum voltage possible on the
meter is about 1/2 volt and this usually protects the meter movement until
the fuse blows.
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     Otmar Ebenhoech         The Electric Speed Shop     [e-mail]
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