This week we mostly deal with wiring issues on the 2008 Cadillac Escalade EXT Electric. The motors are in and we spun them up using a 12v A123 battery module. Very quiet and vibration free.
We mounted two glycol fill bottles, one for our Soliton liquid cooling system and one for the electric heater. It has been over a year since we did the segment on our tankless water heater we are using to heat both cockpit and battery boxes. We'll repeat a lot of that in the next few weeks as we install it. But the big breakthrough is the realization that we could use the windshield washer heater switch to turn it on.
The Cadillac actually has a heater for the windshield washer bottle. I've never heard of this before. And I don't quite get it. The idea of dumping hot windshield washer solution on an iced up windshield gives me a chill, so to speak, windshields costing what they do. The thermal contrast between the heated solution and the ice is pretty great. I would think they would have some problems with fracturing windshield glass.
The system IS under recall, but for another reason. IT has burned a couple of Cadillacs to the ground. The problem is, they don't fix it in the recall. THey just disconnect it and you no longer have a heated windshield washer. We haven't exactly done the recall, but I do intend to disconnect the power to it. It goes through a 60 amp fuse on the fuse block.
Leaving a rather unused, but really quiet prominent switch on the console right below the environmental controls. And so we are going to steal this signal and use this switch to turn on our electric heaters.
The heater assembly we created has pump, TWO contractors, and two heater elements all in one box. We'll use the signal from the switch to turn on the pump and the heater elements. Relays and thermostatic switches will be used to cut OUT each of the heating elements in turn as the temperature of the system rises..
In this way, we'll turn them both on initially. When the temperature gets to 45C, we'll cut one of them off with the thermostat. As it continues to rise, at 55C we'll cut the other off as well. As it falls to below 50C, that thermostat should turn it back on. So it will seek around 50-55C on one heater element.
The pump will pump the fluid first through the cabin heat exchanger. This should provide quite a heat drop to warm the large passenger area. The fluid exiting the heat exchanger will be routed to the battery box where it wanders through a series of loops of pex tubing beneath a false aluminum floor in the box. After leaving the box, it will pump back to the fill reservoir.
The glycol should be much cooler on the batteries than on the passenger compartment, but still warm enough to maintain battery temperature.
I know the universal advice is that these batteries need to be cooled. They do not. They do not under any imaginable load cycle. Instead, what we've found is pronounced improvement in all parameters up around 35-40C. Worse, what we've found is pronounced decrease in both capacity and power at anything below 0C. In fact, it has become evident you should not charge these cells AT ALL below freezing.
And so we are going to heat them. We're also going to heat them in the garage while charging, but with a much lower power 240vac heating pad that we will probably affix to the fill reservoir. This won't do much really. But it will be in a garage when we are charging. And it will go on all night. We think a couple hundred watts will very gradually heat the battery box. The side effect will be a warm cabin on entry in the morning.
The vehicle features a remote door lock and even a remote starting system. We're hoping to retain that functionality. Of course, there isn't much to remote start with an electric car, but if it can get the air conditioning or heating going, that would be cool - or....err.... warm.
We used a Ferraz Shawmut A50QS-1200-4 fuse. This monster is the size of a large orange juice can and costs about $350. Sizing these is a pain, and explaining them, even more so. They are a FAST blowing fuse - that blows slowly. No, this makes no sense at all. Neither does the application guide from Ferraz Shawmutt, at least to me. Basically, this fuse will do 2500 amps for about 18 seconds and 4000 amps for 2 seconds. 1200 amps it will do continuously. This does not sound very "fast" to me. I have contacted one of their applications engineers seeking adult supervision on how to size these and how to explain this. So far, no help.
We're mostly using Champlain Cable COmpany's 4/0 shielded cable on this build. This is 4/-0 of copper wrapped in the using poly insulation, then a steal braid, and finally another layer of insulation. I like this for a couple of reasons. The obvious is the decrease in radiated emissions and noise that can affect other components. We do not have the EMI requirements of Europe, but on the other hand banging 2000 amps of 192volts of energy at 8 kHz is going to put out some stuff. One less thing.
Secretly, the reason I would pay $12 per foot for it is that with the layer of steel braid and another layer of insulation, this cable is much more resistant to abrasion. It's going to be very difficult for it to rub through to the copper and connect with frame. It is surprisingly flexible for what it is.
The Solitons already have TWO contractors in each of them. But I caught Sebastien Bourgouis with another pair in his 911 at EVCCON 2011. When asked, he noted it was just redundancy. Ok. Me too then.
And here's why. With other controllers we do usually have a contactor, but we also have a hand switch in the passenger compartment to break the connection to the controllers manually if necessary. I haven't really worked out a way to do that in the Cadillac cockpit. There is this enormous center console between me and the passenger, and no floor space or bulkhead I could conceivably reach.
I'm really NOT a safety Nazi. Prudence is good. But pontificating about safety is not really my thing and some of the extremes espoused by the wannabe experts and poseurs just seem over the top to me. But we have a failure mode with DC motors that is sufficiently rare to be hardly mentioned, but sufficiently possible to pose a danger. And the danger is kind of frightening.
IGBT's can fail SHORTED. Most of the time they just burn up and are destroyed. But it IS possible, though very rare, for them to fail in a short. In the case of a PWM controller feeding a DC eeries motor, this is like connecting the battery pack directly to the motor. With our motors, and this battery pack, that could be 2000 or even 3000 amps OR MORE. When you break an arc at a voltage of 150 and that kind of current, it tends to vaporize metal, and arc weld contactor contacts. Frankly, our manual switch could well be useless too. And that gives rise not to a sunburn, but a vehicle screaming to go at top speed with 300 or 400 kw of power. Not an attractive spectacle for me.
By adding a second set of heavy contractors, using hydrogen dielectric and magnetic blowouts, IN SERIES with the ones in the Solitons, things are maybe better. The arc welded contacts of one contactor set will not really carry current as well as clean contacts and the immediate, almost simultaneous breaking of a second set stand a good chance of breaking that current flow. And if not, the heat generated in the contractors will within a few seconds cause them to go hand grenade anyway.
So that's the theory. We are using two 500A EV-250 kilovacs each capable of breaking 2500 amps. This in addition to the little EV200's in the SOlitons. We'll connect the 12v actuating signal through a big red slap switch on the panel beneath the steering column. I won't have to bumble or look. It's the only switch there, and all you have to do is hit it to disconnect the 12v from the contractors.
We are using TWO Megapacs on the Escalade at 15v. And in addition to our diodes, we are going to add Jeffery Jenkins recommendation of a 100 uh 14 amp inductor to the input to each, along with a 30 amp high voltage fuse.
So that's what we did this week. This is an enjoyable part of a build. The big stuff that takes weeks is over. Now we see progress every day. Little wiring things are fun for me.
Yes I'll try to schedule a private class for Brian on wireless microphone batteries sometime this week if I can find time.