# Dual Power Source for Heater



## Zappo (Sep 1, 2011)

I don't know if this is clever or just crazy but it has been working very well so far. My 1996 Ford Ranger is running a 288 VDC pack and charges from 240 VAC. For heat, I went with two of the Kat tank heaters from Northern tool. I decided to see if I could power the heaters from either source depending on whether I was driving or parked. To achieve this, I used a set of two SPDT ceramic body vacuum relays. I would have liked to use a single DPDT vacuum relay instead but I didn't find any at a good price.

I decided to use these relays because of their higher current capabilities: 

http://www.ebay.com/itm/New-Vacuum-...921?pt=LH_DefaultDomain_0&hash=item564e58e839

These relays have a 50 amp contact rating and 12vdc coils. They are usually used for switching RF frequencies but are also rated for DC.

Because I didn't know how well this would work out, I installed fuses everywhere. When I applied power, nothing blew up.  Basically, the relay commons are my two output leads. The DC goes to the normally closed contacts and the AC goes to the normally open contacts. This just establishes which power source is available for the heaters. I have a separate Kilovac relay to actually enable the heater elements. When I plug in the 240 volts, it powers my Zivan charger. I'm using the two auxilliary relays in the Zivan to control the vacuum relays. When the Zivan is finished charging, it powers the vacuum relays.

Since I don't have a garage, I wanted something that would preheat the car before I needed to drive to work. That way, I'm not using the pack to initially heat up the passenger compartment. Besides, it is so nice not needing to scrape the windshield when it is freezing out. Originally, I just had a toggle switch to disable it when I didn't want it coming on. I recently added a remote control relay. Now I can start it heating from inside the house when I first get up and it is toasty warm when I go to leave. 

To control the temperature, I installed an inexpensive 12vdc panel mount temperature controller. For about $15, this is a pretty amazing unit from China. It has a relay output and can be programmed for heating or cooling. You can adjust the differential between where it turns on and turns off the relay. It even has a calibration offset and an adjustable time delay. It only reads out in Celsius, but that's okay.

The controller only operates the relay for the tank heaters. The pump and blower fan run as long as heating is enabled. I was very surprised on how easy Ford made it to power the blower from an external source. The main heater fan relay is wired to be energized when the key is on. They were nice enough to bring the incoming power to the normally open contact of the relay and the fan is on the common. I only needed to supply 12v to the normally closed contact to run the fan. The fan speed control works exactly the same when heating from either source.

I was originally using a 240VAC to 12VDC charger when plugged in. The charger wouldn't work on DC. I was just driving off the battery when driving.I now have one that will work on either AC or DC. I'm thinking of changing things around a bit to try this dual power idea for this too. The worst I could do is blow things up, right?


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## GizmoEV (Nov 28, 2009)

That is great. I use the aux relays in my Zivan to turn my CycleAnalyst on when charging and off when finished. It works just great. I wish all chargers had similar relays.


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## Zappo (Sep 1, 2011)

Thanks David. 

It looks like my trip to work takes between 18 and 21 AH without heat and 22 to 24 with heat. Since the heater elements draw about 15 amps from the pack, that number will probably climb a bit as it gets colder. Looks like I sized the pack okay. I'm still going to try setting up to charge at work also. That way, it can be toasty warm from the start then too.

BTW, I took your advice on the Zivan programming. Looks like it is working great. You are right. There is very little energy between 3.5 and 3.8 VPC.


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## GizmoEV (Nov 28, 2009)

Zappo said:


> BTW, I took your advice on the Zivan programming. Looks like it is working great. You are right. There is very little energy between 2.5 and 3.8 VPC.


Great, glad it is working. BTW, I assume you meant 3.5-3.8V

Over the past couple of years I have been lowering my ending voltage a little. I'm now ending at 3.455V and the resting voltage the next day is just under 3.4V so I think I'm getting close to 100%SOC without overcharging. What I don't know exactly is what the parasitic load current is on my pack. I know that my Battery Bridge circuit only draws about 0.34mA and the DC-DC draws at most 10mA with no load. Maybe the radio and balance meter draw 1W so only about 14.5mA from the pack. Total less than 25mA from the pack so sitting over night after a charge only 250-350mAh have been taken out of my 200Ah pack. I think I have thing set about right now.

What are you using for your ending voltage now?


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## Zappo (Sep 1, 2011)

Sorry I didn't answer earlier Gizmo. I didn't notice the question The charger ends at 319 volts, which is 3.54 VPC. I'm really going to need to do some detective work now though. It seems my AH meter has lost its accuracy. It claims I am using 5 to 7 more AH than before for the same trip to work. I've compared the numbers with and without the heater. They are both higher. Even more odd is that every charge ends claiming 2 to 4 less AH into the batteries than the previous charge. So far, the ending VPC indicates nearly full charge each time. All 90 batteries are staying tightly together in voltage, Usually 3.38 to 3.4 volts after sitting a while. Since this has happened over the last 10 or 12 charges, I would think the batteries would show they were coming off full by now. Probably something I did while cleaning up some wiring but very strange.


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## GizmoEV (Nov 28, 2009)

Does the Ah meter read zero current when there is in fact zero current? I know my CycleAnalyst drifts. It appears to depend on the temperature of the meter. Maybe your meter is reading "fast" on discharge which would show as "slow" on charge. You might get a good low current hand held clamp on Amp meter to see what the current really is during charge or some slow draw and compare that to your meter.

Remember, too, that the temperature of the batteries will affect the Ah consumption rate. Maybe that is what you are experiencing.


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## Zappo (Sep 1, 2011)

The meter does read zero when there is no draw. There is no doubt that the colder weather is taking its toll too. I think you are on to something about the "fast" discharge versus "slow" charge. I timed how long it should take to charge based on the charge current. It took the expected amount of time but was 4+ AH short of zero. The batteries settled to 3.41 -3.42 also so I'm sure the are fully charged.

While waiting for the new heater to arrive, I'm going to try "slow" discharging the pack and then charging it back up to see what it shows.


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