Hack-charging on a generator

[andrewket]

I have two APC Smart UPS that have a config item for running on a generator. With it enabled they don't constantly switch.

 

[smorgasbord]

I have two APC Smart UPS that have a config item for running on a generator. With it enabled they don't constantly switch.

Well, there's a reason your UPS unit by default doesn't like the power from your generator. Adjusting the sensitivity is literally saying that you're OK with non-ideal power going to your equipment. So your UPS unit ends up acting mostly as a surge supressor and nothing else. Most residential units don't clean up the power - they simply provide surge protection, and in case of brown-outs or loss of power or other bad power conditions they provide their own power. The adjustment lowers the threshold for what it thinks good power is, and than passes that power to your equipment. And when the UPS units are creating power from the battery, they don't generate very clean power themselves, with "modified sine waves" and all. Computer power supplies are OK with that (because all they do is create DC), but I'd worry about TV/stereo equipment.

One interesting experiment to try if you have two units is to see when connected in series if the second will accept the power produced by the first (which isn't plugged in to the wall). If not, then the UPS isn't even creating good enough power for itself!

The double-conversion/dual online UPS units are always making their own clean power, so they not only (usually) tolerate generator power, but can clean it up. I have a Liebert online UPS that didn't like my old generator power, but the 2 Tripp Lites I've used were fine.

Anyway, I think the cheapie UPS's you buy retail for under $200 are suitable only for computers and wall warts - be careful using them for anything more sensitive, even without a generator involved.

 

[miimura]

The normal Smart-UPS is a good true sinewave unit, but it is standby, not double conversion, so it's only making a nice sinewave from battery. So, if it accepts the power coming from the generator, it's just passing it through to your equipment. Not good for traditional generators. You need the Smart-UPS On-Line (also called Smart-UPS RT) to get double conversion so it will clean up the power.

 

[cinergi]

OMG, I spent 30 minutes skimming that. I actually found the section on lighting and color rendition fascinating, but that's OT here. It repeats itself - what I think has happened is that as new models come out he re-edits his old spiel for the differences and then just appends it to the bottom. So, after all the discussion the EU6500is, for instance, there's then a section on the newer EU7000is.

I just bought a EU7000is for home backup. It's interesting to read how even the older EU6500is could handle 7680 watts, but Honda had to de-rate it for North America due to GFCI requirements and home standby power regulations. I wish I could summarize the whys, but I can't - it has to do with floating versus bonded neutral/ground. How much draw did you attempt from your EU6500is when charging your Model S? I saw someone here say it was the equivalent of 17MPG. The newer EU7000is is supposed to get better fuel usage (being fuel injected instead of carburetored), so perhaps that gets close to 20mpg.

As for miimura's reference to double-conversion (also known as dual online) UPS systems to clean up power, that's what I used to do with my previous smaller Coleman generator. Most UPS's won't work with contractor grade generators, but my Tripp-Lite "smart online" UPS system did. And since it's always taking AC power to DC and then reconstituting AC from DC, it doesn't matter what the power coming in looks like (within reason, of course). I had my TV/Computer stuff plugged in this way. 110 volt systems can be had for under $300 on ebay.

It's an oddly addictive read. I think I ran 27 maybe 28 amps off of it before I'd see it complain about overload. And even then it's only rated for 6500 peak unsustained. It handled it fine tho.

 

[cinergi]

I needed to rebuild the carburetor on my EU6500is so what better way to test a full load than charge my car? Plus I wanted to see if I could charge directly off of it by bonding neutral and ground. Success!

 

[redi]

Very cool. Thanks for posting about the N-G bonding plug.

 

[kkitzhaber]

Going WAY back, I was able to make a 20+ year old generator charge my Model S. On Craig's List, I found a Coleman Powermate 5000, with NEMA 6-15 plugs. No owner's manual on-line for this one. It's replacement model used the NEMA L14-20. First step was to bridge the neutral and ground on the 120V plug. First attempt, the car started charging momentarily and then rejected it, even at 5 amps. It was showing the voltage fluctuating from 235 to 245V as the generator wouldn't maintain a stable speed. SOLUTION. I put a resistive load on the 120V plug: 500-1000W space heater. After I added that and adjusting the choke with the load, the loaded generator happily stabilized at 242-244V. Then, I plugged in the car at 5 amps. After waiting a few seconds, I disconnected the space heater, and the generator maintained a steady speed. I cranked it up one amp every few seconds until it quit... at 13-14 amps. Generator nameplate shows the old generator will handle up to "15 amps" on the 240V plug, or 21 amps on the 120V plug. The mystery is... why is it rated for 5kW when all I can get is about 3kW before the car says 'enough'? Perhaps it will handle a purely resistive load up to 5kW? Maybe the car's AC-DC converter is kicking back enough interference to cause the car to stop charging? Must be the car, because if it were the generator, the circuit breaker would have popped. The gen's 240V has a 20A breaker, and the 120V side has a 25A breaker. The moral of the story: You CAN teach an old gen new tricks. A ~$100 ol' school gen WILL work in a pinch, if you do a G-N bridge, and load it right.

 

[Electric700]

What if you just do a ground to earth wire (without a neutral to ground bridge) and no secondary load like a space heater? Will it charge then?

 

[Svandevo]

I wonder if a whole home generator like http://www.generac.com/Residential/Guardian/Products/Guardian_Series_17_kW/ Would charge the car.

Yes it will. My 20 KW charges it just fine.