Hybrid by connecting controller to inverter generator

[quuxman]

I've been thinking about lightweight hybrid electrics for 10 years off and on (mostly off). Fuel cells systems on the market unfortunately still do not have practical power density, so that leaves gas generators. I recently came across this little unit:

http://wholesaler.alibaba.com/product-detail/lightest-800w-portable-camping-gasoline-power_1830681806.html
(see my post about generators)
https://endless-sphere.com/forums/viewtopic.php?f=14&t=66297&start=25#p1202709

This looks like a really good option for cheap and light power. However, it looks like getting the power to the controller isn't going to be exactly straightforward. Looks like an 800 W 120 to 50 V adapter would not only be expensive, but really big too. Would it be reasonable to hack the existing inverter on this generator to add a 50 V output at full power?

Once I get the 50V from the generator, I imagine I'd need to add diodes between it and the controller to prevent overcharging the battery?

I'm planning on installing this generator on a little 2 wheel trailer, that connects to my existing electric system with a power plug. I'm also considering adding a battery to the inverter, so I can power a laptop and music hardware without running the generator continuously. Ideally I could separate the battery+inverter and leave the generator behind for shorter day trips.

Thoughts?

 

[quuxman]

So I talked to a seasoned electrical engineer about this project, and got some very useful advice. She said switching power supplies are daunting even to a well practiced EE, in fact are an entire EE specialty. Unless I wanted to do a lot of studying, some serious engineering with a circuit simulator, and fry several devices, and spend a lot of time, don't try hacking the inverter. I should just get the 120 to 50V supply, even if it's a bit big and expensive.

As to connecting both the battery and generator source to the controller, simply separating both with a diode as I was initially imagining would work, but has some problems. She said 100 V schottky diodes would be the best kind of diode, but each would create a .5 V drop, meaning with my current 25 amp controller I'd have to dissipate up to 13 watts in heat! This would also present a potential problem of discharging the battery even when the load can be provided with the generator. The ideal solution according to her is a lot more complex than I was first imagining, and involves a fair amount of logic and a relay or two. Here's what I'm thinking so far: start with the two diodes, and some switches, and do some measuring. Then in order to not have to toggle a switch in order to go past half throttle or have the battery draining all the time, build the following logic:

The logic circuit (most simply done with a micro controller) would measure load on the generator and if it's on. When the generator was on, the relays would disconnect the battery as well as short the generator diode (to prevent waste heat) until the load on the generator surpasses a certain threshold beyond the generator's continuous power and below it's peak power. Once this threshold was reached, the logic circuit would reconnect the battery (not sure if battery needs diode or not in this case) and reconnect the generator's diode to prevent the battery from messing up the 50 V power supply. When the generator is off, naturally the battery is simply connected to the controller as normal.

Does this make sense? The logic circuit would prevent the battery from being drained when the generator was on, and allow only generating waste heat when drawing more load than the generator supplies. Is there a simpler solution?

 

[parabellum]

1)Generator to
2)AC CC/CV charger (under 800W, better under 650WP.S.- under 500W according to your other tread post) to
3)battery (without exceeding its max. charge capability, be careful if you have regen, it adds to charge current)

 

[quuxman]

P.S.- under 500W according to your other tread post

Why under 500 watts? What post? Without seriously harming my battery, I can only charge it at about 200 watts, 15% of the bike's full power, which is not acceptable. With the generator I have picked out, I'm going for 700 watts (54% total power) continuously, without discharging the battery. This means I have to isolate the battery from the generator. I'd say a power supply rated for at least 800-900 watts would be appropriate, so I'm not running it at maximum capacity for long periods.

Where could I find a 800-900 watt 120V to 50V converter? I've looked quite a bit, and the only thing I've found that's reasonably close is on Digikey and costs over 300$, which seems excessive. It accepts an 85 to 265V input, which I definitely don't need or want. I have a stable clean 120V AC source.

http://www.digikey.com/product-detail/en/tdk-lambda-americas-inc/PFE700SA48/285-2317-ND/4833527

Another option that's occurred to me is getting 6-8 cheap 50V ~2A power bricks and wiring them in parallel. Is this a bad idea?

 

[parabellum]

Why under 500 watts? What post?

https://endless-sphere.com/forums/viewtopic.php?f=14&t=66297&p=1202718#p1202709

Where could I find a 800-900 watt 120V to 50V converter?

2 of those in series http://www.ebay.com/itm/400W-24V-17A-Single-Output-Switching-power-supply-AC-to-DC-SMPS-/261847204022?hash=item3cf74f40b6:g:J4sAAOSwEeFVKTh4 (but must probably isolate ground)
or this in parallel http://www.ebay.com/itm/321837420934?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Those are CC/CV type according to this thread https://endless-sphere.com/forums/viewtopic.php?f=14&t=75212 , so will not experience hiccup shut down if overloaded. You can also adjust current and voltage limit.

 

[parabellum]

Does this make sense? The logic circuit would prevent the battery from being drained when the generator was on, and allow only generating waste heat when drawing more load than the generator supplies. Is there a simpler solution?

You could have PSUs adjusted to give highest system Voltage on controller end (defined by battery full voltage) and battery going to controller over diode. Whenever PSUs are overloaded to CC mode, voltage will fall until battery voltage and battery pushes missing amps one way, over diode. When load falls, PSUs voltage rises and it takes over again. For battery only you just short the diode with a hand switch.

 

[quuxman]

voltage will fall until battery voltage and battery pushes missing amps one way, over diode. When load falls, PSUs voltage rises and it takes over again. For battery only you just short the diode with a hand switch.

I like this suggestion. I was wondering if something like that is possible. However, the more I think about this, the more I think hybrids are kind of ridiculous. It's a lot of extra pieces and complexity when I could simply spend 500-1000 bucks and get a big secondary battery, and save myself days of working on it, and save an enormous amount of space on the vehicle. I'd definitely want a fast charger for that size of battery. Oh boy, another thing to research

 

[parabellum]

I like this suggestion. I was wondering if something like that is possible. However, the more I think about this, the more I think hybrids are kind of ridiculous. It's a lot of extra pieces and complexity when I could simply spend 500-1000 bucks and get a big secondary battery, and save myself days of working on it, and save an enormous amount of space on the vehicle. I'd definitely want a fast charger for that size of battery. Oh boy, another thing to research

That is optimal, when battery is enough for your longest ride. Do not forget, your charger should be not faster then your battery. PSU's I linked is the best bang for your buck for charging but Eltek flat pack psu kicks asses by density and efficiency.

 

[nki]

before I could afford batteries I ran my electric truck off a 5kW generator. It was the older style from late 90s with a "13 HP" honda clone, with the brushed generator head. I rectified it straight on to the DC bus with no batteries. It worked well enough to move the truck around the yard.

[youtube]tJIlIdhn4EM[/youtube]

further implementation details here:
http://nkirkby.scripts.mit.edu/nk/derptruck-preface/

This person has implemented a power system which is similar to what you describe.
[youtube]iYR4344zpTw[/youtube]