Volt Inverter hack

Alternative energy sources
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The usual. As I have two large solar PV systems here, and my lab assistant just put one in, and others are interested in things like this, here's where that stuff goes. This is mostly for things that work now, not "gee someday a fusor will do this" -- we know that, but it's not someday yet.
The hope is to save anyone embarking on this sort of thing a lot of wasted time and money, as at least I have been off the grid since 1980 and have had a lot of practice (and made mistakes you won't have to).

Volt Inverter hack

Postby Doug Coulter » Tue Jan 24, 2012 6:33 pm

One of the reasons I could justify the cost of this car is that it can also be a backup generator for the house. While there are more ambitious projects in my mind (as in doing this right off the main battery), all I really need to keep up and charge my house is something under a kilowatt - houses are easier loads than automobiles. This is because I have a large house battery (about the same size as the Volt - 16kwh), and inverter system that can handle peaks no problems - so to keep up and trickle charge the house, I only need to make the average power or a little more. My home only uses a KW when I'm running machine tools, a bunch of computers, welding, my fusor, stuff like that - most of the time I'm using about 250w or so, so this will be plenty.

The Volt has a 12v auxiliary system that is capable of 175 amps - much more than I need, but of course, you don't dare use it all - other things in the car may come on, and this system is responsible for running all the various accessories that would normally be belt driven in a regular car - some of those can use real power for hydraulics, air conditioning, coolant pumps, and other such things. I settled on a bit oversize inverter - 1300w or so, which I won't actually use all of - always nice to have some margin. Harbor freight had some pretty cheap, so I just got one there. If you were going to use this AC for anything "serious" you'd get a better sine wave one from Xantrex or similar, but here I'm just going to be running a 35 amp 24 volt battery charger, which doesn't mind square waves, in fact, prefers them. A problem I had is the Volt's 12 APM (charger) is all over the place - from 13v up to about 15.3, and anything over 15 trips the cheap inverter's overvolt safety and shuts it off. GM didn't want to cooperate on fixing that for me - it's bad for that battery too - so I munged the inverter itself instead. This inverter uses 5 170 volt DC step up supplies in parallel - big fets driven off a uP, then a full H bridge to switch that into 120v AC. On cursory analysis, I realized that the uP is doing the voltage sensing and that this is probably to protect the gate oxide in the FETs, so I only really needed to drop the volts to the uP and the FET gate drivers, not the entire thing (good, it can draw real amps!). So, since I wanted to remote the switch anyway, and that's what it switches, that's what I did - and while I was at it, I added a diode drop in the switch circuit.
So, lets show some pix.
InverterGuts.jpg
Inverter guts

This shows the guts of the inverter, with it's 5 switchers to make a bunch of 170v DC all in parallel, and the output H bridge. This inverter doesn't tie neutral to ground for what that's worth - some things wouldn't like that (maybe you could tie it, I didn't try).
InverterMod.jpg
Inverter post mod

So, after figuring out which switch wire was the supply and which the load, I removed the switch and spliced in some good quality wires instead, using a tie wrap to secure them inside the inverter against being jerked out. Since I wasn't sure this would work, or how much drop I needed to make it work, I didn't do any other mods in there - this thing is hard to take apart, and half the screws are security torx (which you can also get at HF while you're there). I put the diode on the new switch instead.
InverterSwD.jpg
Switch and diode

Since polarity matters, you can see why I used two colors of wire here.

Something like this needs some fat feed wire. I made up some cables and did some slight mods to the battery lugs - one needed to be drilled and tapped to get another connection. The other one (gee, you probably should NOT try this one at home) had a bolt already for the existing wires. What I did there - which is "touchy" to say the least, is carefully take off the existing bolt - WITHOUT losing continuity in the existing wiring, which has nasty efffects on the car computers, and added my new cable under it. Working with solar system will teach you how to do that - batteries don't have a power switch, you have to learn to work on things hot. Here's what that looked like when I was done. For this picture, I had the plus wire taped on the inverter end and stuffed back in the battery cover so I wouldn't have an "issue".
BattWires.jpg
Battery with new wires


For what it's worth, this spot is not too hard to get to - you lift the hatch cover board (there's a handy little bungee to tie it up) and take out 4 nuts to remove the protective plastic battery cover. Bingo. To really get access, you pull forward on the cover board a little, and it and the hinged back part all come up, but then you have to prop it up another way, the bungee doesn't do it at that point. Watch your head.

You might notice there are a lot more extra studs in there. It turned out in this case that this inverter is a perfrect fit between a couple, so I didn't bother making a special baseplate and mount, it wedges in there tight and never moved in a month of driving - some hard. I suppose a perfectionist would make a plate and bolt it down. I just wanted this to work with minimum effort on my part, and least weight.
Here's what it looks like in there now:
InstalledB.jpg
Installed

I just plugged a power strip into the AC output, and threaded that into the left side removable panel, which I'll show in a little bit -- all the inverter wiring go there. This is surprisingly robust, once it's wedged in there it doesn't rattle and it's actually hard to get back out.
SwDetail.jpg
New on off switch mounted in compartment

I put a new switch in there - as easy as this GM plastic is to carve (too easy when it's new, it's hard to hole it without melting it) I just put in a mil spec toggle instead of the original, which would have required a square hole - I was running out of daylight and temperature, and I don't have a garage.
The fat wire trailing off to the upper left is the power strip cable. Here's a pullback shot.
CarMods.jpg
Pullback shot of car mods, switch and slot in cover plate for the AC wire


I just cut a slot in the bottom of the cover to pass the power strip wire, and when not in use, I just put the power strip in the mesh grocery bag I got for the car. This is a pretty seamless mod - nothing doesn't fit right, I can still use the nice rubber mat back there, all that - and fairly invisible when the power strip is in the bag.

Of course, I had to test it. Here it is running a big halogen work light.
Working.jpg
Working!


So, when done, you just put the plastic cover back in and bolt it back down, put the acess cover back, and in general put things back the way they were. Now I have volts outa my Volt!
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Doug Coulter
 
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Re: Volt Inverter hack

Postby Doug Coulter » Tue Jan 24, 2012 7:13 pm

I should add for the members here - this is enough power to run a demo fusor that will fit in the back of the car...so I can take it on the road and do demos...Since the car got the FUSOR license plates from the Camaro - it's perfect.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Volt Inverter hack

Postby Jerry » Wed Jan 25, 2012 4:06 am

No, no. Everyone knows you are supposed to install fusion reactors only on DeLoreans.
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