Series Hybrid Generator Control
Hello,
This is my firs post to these forms. I searched around a bit a could not find an answer to my question, but my apologies if this has already been asked.
I'm currently involved with a team working to convert a 72VDC EV to a series hybrid vehicle. We use a lead acid battery bank and an AXE controller. We have built a ICE-72V DC Generator system and are working to integrate it into the EV to make it a series hybrid.
I can't seem to find any info on the control interface between the DC generator output and the rest of the vehicle. Can we just plug the generator directly in parallel with the battery bank and expect the system to maintain an equilibrium between charging and discharging depending on the motor controller load? Is some form of DC-DC Lead Acid battery charger required? What is the standard method of integrating a DC generator output with the battery bank and motor controller aspects of the system?
Any information would be greatly appreciated.
Thanks for your help,
Andy
On evcomponents.com they carry some DC-DC converters made by Iota that are also battery chargers. However they may be too high a voltage for your system.
The reason you'd want to use a DC-DC/charger rather than a straight DC-DC is because of charging algorithms. Charging algorithms aren't a steady state current/volts, but a straight DC-DC provides a steady state of current/volts. Instead charging algorithms vary current/volts as the charging progresses so that the battery doesn't get overcharged.
On the other hand if the generator simply outputs 79.2 volts (6 x 13.2) the battery pack won't be overcharged.
A question would be whether you can find (or afford) a DC-DC with power capacity that matches your generator. A useful generator in a race vehicle could be 10kw or more? What are you looking at?
There's a book - The Zero-Carbon Car: Building the Car the Auto Industry Can't Get Right - by William Kemp where he goes through designing and building a PHEV car. And while his car carried an on-board DC genset (10kw) he didn't cover the details of connecting the genset to the battery pack. His design however does include a regular battery charger.
What I was getting at two paragraphs up is - use the genset not for charging the pack to its optimum but simply to maintain the pack during driving. Then still use regular chargers to give the pack a proper charging. This may be what Kemp did with his car.
is the generator you are putting in more than the average load? (wh/mile * mph)
are you planning on running it while not moving?
if the answer to both is no, then just connect directly.
btw, if you don't already own a generator, make sure you get an inverter model.
the inverter modela (as in all of them) already have a DC bus to direct connect the battery pack to.
Matt
Andy
How much voltage does the 72 volt generator really make and how much under max load? I had a 120 volt S-10 and a DC generator and it did 1 or two amperes most of the time and 50 amp stepping on the pot box. It never really charged my battery pack just kept voltage under acceleration a tad bit higher. I quickly went up to 144 volt with a Vanguard Briggs and Stratton Engine and 7.5 KW AC into an old Lester battery charger of the SCR type keeping the batteries at 150 to 160 volts most of the time. I found out the engine power bogged down to maintain about 6 to 7 KW and the circuit breaker popped only once. The reason why the 120 volt generator didn't charge much is because you measure Pb under load and it should be 2.1 v/c so a 120 volt pack is about 132 volts charged. and when it is 120 to 123 or so it is near dead or DEAD. I went from New Bedford MA to Bellingham MA starting with a full or nearly full charge and generator was maxed out near Woonsocket RI. As a range extender I think off of the top of my head it might give you some real range.Figure how many amp it is required to fill EV and how far you can go, and you can get an idea of amp hour per mile you need. I had a net loss using 7 KVA and truck required about 10 or so KW. BTW is the Motor designed for Generator? If so it will bog down also and not make more than generator can do. Therefore keeping it from burning up.
Rusty
Bi the way, Buy the weigh or some thing like that?
What do you mean "BTW is the Motor designed for Generator"? I'm afraid I don't understand this.
Thanks for the help! More thoughts are always welcome...
-Andy
I had been experimenting with gas engines and generator heads and most gen set come with just enough power to bog down like a 14 HP engine making 14 HP of electrons. I tend to use what ever engine I can find which is usually too big and hook up a Generator head to it by belts or spline shaft and going that route if you draw too much current, you fry the windings. I just got off of eBay a 3KW 240 volt diesel gen set and use a switched mode charger 107 Ampere @ 28.8 volt. It uses maximum power of diesel and charges battery pack during power outages. when the battery pack gets up to nearly full it shuts off. This way my inverters do all the work up to 10 KVA peak and for 5 hours 6 KW. When voltage gets to 21 or 22 volts on pack a relay or contactor starts up diesel to top everything off. Reason is why use diesel oil for 1 or 2 KW, just use maximum efficiency.Oh the reason I use diesel is to use french fry grease. I use two fuel tanks.
Feel free to call me or email me.
Rusty
Andy,
Did you end up putting the generator in? If so how did it turn out. I am thinking of doing the same thing in my vw beetle electric car.
Thanks,
James
If you don't mind answering a couple questions
Out of curiosity, did you build the generator?
What amps was it putting out?
Was it DC or AC power that the generator produced?
I have been looking for a DC generator with 80 volts and 100+ amps without much luck.
"a charge controller between the generator and the battery bank"
That's exactly what I have been looking for. I suppose I will need to contact an electric engineer. Or maybe come up with a backflow circuit to avoid the backflow problem at least.
Why would 80 Volts mean less back-flow? Does it have to do with the batteries? Thank you very much for the links.
Hi Andy
I am quite a newbie here and will really appreciate your sincere help.
How did you manage to control the generator current in case of regenerative braking? If I am not wrong regen would flow in current in the battery and meanwhile gen is also engaged in pumping in the current to it. So considering a limit to the charging current in battery how did u managed the process?
Regards
link4pp
The generator will be outputting constant power. Thus it could be above or below the instantaneous motor load depending on acceleration, driving conditions, etc.
Is a disconnect switch required to uncouple the generator from the battery bank when it is off? Will this keep the battery bank from spinning the generator like a motor when it is not being force driven by the ICE? Is some form of high power diode required to prevent the batteries every spinning the generator?
I've tried to hunt down a 72V to 72C DC/DC converter or battery charger, but there isn't much out there. We could use an alternator to convert to AC and then use a standard wall charger, but this seems inefficient...
Plugging the generator in directly to the batteries in parallel with the controller would be the easiest approach if I can get away with it. Any small things I should do to make this cleaner (filter caps, diodes, etc)?
Thanks for the input!
-Andy
Andy Sayler
Tufts Hybrid Racing
Tufts University
Medford, MA