[dtbaker]

ok.... out of sheer frustration, I took the fuses out, and replaced with single strand 22ga telephone wire 'fuses'. Everything seems to work fine. Added diode back in, still works fine. Nothing caught on fire or melted. Makes me a little nervous, but will have to do for now.

Looking at my HV ammeter, which is analog needle 0-500 amps, it is hard to be exact, but it looks like the heater is pulling between 20 or maybe 25 amps (at about 100v - 96v nominal pack). The whole problem MAY just be that the core is pulling just a little too much for the fuses at my particular voltage.... but it seems like a lot.

I have a friend w/ DC clamp ammeter I will try to see what it is actually pulling more accurately, but not till week after next.

I would still like to know if this higher than expected draw COULD be a sign of some minor damage to the core, or if it is likely this is just what it is going to pull. I would hate to get a $125 dollar replacement, go thru the pain of replacing it, and have the same results. I also am wondering why the cores on various EV sites are so expensive compared to cheapo heaters from Walmart and what the difference is between the ones listed for different voltages.

[dtbaker]

ok... new learning experience with the heater... I was driving along last night, almost home, and pack was down to about 70% DOD; its been cold and I had taken an extra side errand. Lights on, heater on....

As I came off a stop sign accelerating up the last hill, pack voltage was sagging down to about 70 (96 nominal).... and the heater went cold.

Turns out that one of my 22ga wire 'fuses' had BLOWN! Melted! wow, I dunno what current, and it might have found a thin spot in the wire right where I stripped off the insulation. But it made me think...

Of course, as pack voltage sagged and the heater was still attempting to put out 1500 watts, the amps went up pretty high! so, lesson in fusing these things.... I still don't know how high I need to fuse to not blow under the extreme condition of running at fully 'sagged' voltage and not exceed the capacity of the fairly thin wire that I remember was connected to the core itself!

[ZEVUtah]

Originally Posted by dtbaker

ok.... out of sheer frustration, I took the fuses out, and replaced with single strand 22ga telephone wire 'fuses'. Everything seems to work fine. Added diode back in, still works fine. Nothing caught on fire or melted. Makes me a little nervous, but will have to do for now.

Looking at my HV ammeter, which is analog needle 0-500 amps, it is hard to be exact, but it looks like the heater is pulling between 20 or maybe 25 amps (at about 100v - 96v nominal pack). The whole problem MAY just be that the core is pulling just a little too much for the fuses at my particular voltage.... but it seems like a lot.

On my ceramic heater I just used a 20 amp fuse. The pack is 144 volts, so that is a bit different than your setup. Have you tried just running a 30 amp fuse instead of the 20 ?

KJD

[dtbaker]

Originally Posted by ZEVUtah

On my ceramic heater I just used a 20 amp fuse. The pack is 144 volts, so that is a bit different than your setup. Have you tried just running a 30 amp fuse instead of the 20 ?

KJD

I have not gotten back to radio shack to see what else was available. My plan was to borrow a clamp ammeter to get an exact pull at a known voltage, and then triple it. But now I think I will adjust further to assume full load of 1500 watts at sagged voltage of 60 volts..... my only fear is that the pigtail wires on the core might not carry the amps at that voltage?! My power leads are nice fat 10ga wire, but the internal wires on the core were made for 120v AC probably!

[tomofreno]

Isn't the heater just resistive? If so it will put out whatever power = V*V/R where V is your pack voltage and R is the heater resistance. So as pack voltage drops, so does current through the heater, I = V/R, and the power output. I would expect it to have less current through it at lower pack voltage. The power rating is likely just what it puts out when plugged in to 120VAC. Maybe something shorted B+ to B- in the core, or the path to the core.

[dtbaker]

while I am not an EE... my understanding of the way ceramic heaters work is that the resistance goes up with the temp so that they self-limit at 'approximately' a fixed temp. To me, this means that if the V drops, the A must go up to maintain the Watts to reach the fixed temp.... right?

[dtbaker]

I can't find any 1-1/4 250v rated above 20a.... but there are auto blade fuses at 30a and 40a. Does anyone know if they would be 'safe' to carry the load at 96v (nominal)?

probably at least as safe as my use of a strand of 22ga wire?!.

[Wistar]

The heater is just a resistance heater, but it has a high "temperature coefficient of resistance". The problem is that when you first turn on the heater it can be very cold and so the resistance will be very low. It can take a minute or two for the heater to warm up, and hence for the current to drop (assuming for a minute that there is no fan involved yet). So, during this warmup period the current will be high. The higher the voltage, the faster the heater will warm up and the current will go down. Assuming slow blow fuses, this might explain why someone with a 144vdc pack would not see fuse blowing while someone using the same heater element and fuses with a 96 volt pack does see fuse blowing.

I put together a little test on my bench at 36 volts with a heater element that is rated for 36 to 72 volts. It is probably about 65 F in my shop, so this was the starting temperature of the heater element. When I switched on the heater, the initial current was about 37 amps. Over about a minute (I did not time it), the current dropped to 2 amps.

I then placed a ducted fan up to the heater element. The current rose to about 12 amps and leveled out. As the fan removed heat from the heater, it cooled down, the resistance decreased, and so the current increased.

All of this was done with terminals 1, 3, and 5 connected to +36 and terminals 2 and 4 connected to "0" volts.

One solution to your problem would be to connect teminals 1 and 5 to the + battery terminal and terminal 3 to the - battery terminal. This will yield a higher nominal resistance. Of course this will also yield less heat as V is constant and I will drop.

A second solution is to put two heater elements in series.

Or just put in bigger fuses! I would not use automotive fuses without doing some research. Many of the automotive fuses I have seen the specs on are rated for 36 volts. At 96 volts, the fuses may continue to arc and conduct current after the fuse has "blown".

[dtbaker]

Originally Posted by Wistar

I put together a little test on my bench at 36 volts with a heater element that is rated for 36 to 72 volts. It is probably about 65 F in my shop, so this was the starting temperature of the heater element. When I switched on the heater, the initial current was about 37 amps. Over about a minute (I did not time it), the current dropped to 2 amps.

hhhmmm, thanks for testing!

Tells me that the current could be quite high for 'a while' if the car is very cold.... and that I am better to turn the heater on, and leave it on while driving; being sure not to switch on while the voltage is sagged under load!

I am installing a Cycle Analyst, and then will have a better idea of actual amps so I can buy proper fuses. It might be overkill, but perhaps I should buy an AC rated circuit breaker? I couldn't find a 250v rated 40amp fuse in local shops yet....

[tomofreno]

Digikey has these 30A slow blow, 1/4" fuses by Littelfuse for $0.75 each:

http://www.littelfuse.com/data/en/Da.../325P_326P.pdf

I plan to put a portable ceramic heater plugged into a 120VAC outlet in the car for ~1/2hr before I leave to heat it up on very cold days to reduce the heating requirement from the pack.

Thanks for the testing Wistar. Good data! I turned mine on for maybe 20 seconds the other day and was surprised no heat came out just cool air. I checked, and it had voltage, 20A fuses were good. I have it wired in series with the blower switch so it won't run without the blower on. Sounds like I may not have waited long enough for it to heat up.

Tom