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.
- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
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
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
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
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
KB1UKU
Rusty,
The generator puts out about 80 Volts. This can be adjusted down by manipulating the throttle on the ICE.
The generator/ICE combo outputs about 7 HP (5 kW), meaning it puts out about 70 Amps between 70V and 80V. The motor draws 50-200 Amps depending on load, acceleration, etc.
Due to simplicity and time constraints, we'll probably start by trying to connect the generator straight to the batteries with a disconnect relay to decouple it when it is off or when the batteries are charged and the car is not moving, etc. I hope this will keep the generator providing extra current when accelerating (and maybe charging the batteries in the CC parts of the Lead Acid charging curve) while allowing us to disconnect the generator is situations where it would be detrimental (ICE out of gas, batteries fully charged), etc.
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
Andy Sayler
Tufts Hybrid Racing
Tufts University
Medford, MA
Bi the way, Buy the weigh or some thing like that?
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
KB1UKU
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
Owner of a 1973 VW Super Beetle Electric.
Hi James,
We ended up running the generator in parallel with the battery bank driving our motor and using a switch/contactor to insure it was only connected to the bank when we were drawing current (i.e. driving). This was done to avoid force charging the battery bank, possible damaging it, and to keep us from spinning the generator as a motor when the ICE (responsibly for during the generator) was shut off.
It worked okay, albeit with the kinds of problems you would expect from such a 'kludge' of a solution. Most notably, we ended up damaging our ICE when it ran out of gas during one of our runs. The driver failed to disconnect the generator and as the ICE started to die, the generator turned into a motor, reverse spinning the ICE and shearing the ICE drive shaft.
In the future, we'd look to the more graceful solution of actually having a charge controller between the generator and the battery bank. This would avoid the reverse-flow problems, as well as allow us to do maximum power-point tracking and other control schemes to maximize the efficiency of the system. Unfortunately, such controllers arn't exactly off-the-shelf components, so designing and building one is a project in and of itself.
Cheers,
Andy
Andy Sayler
Tufts Hybrid Racing
Tufts University
Medford, MA
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.
Owner of a 1973 VW Super Beetle Electric.
We were using a Marshall ME0709 COTS generator (http://www.marselectricllc.com/me07091.html). It's a DC generator that we ran at about 125 Amps and 72V (I wish it had been 80, fewer back-flow issues that way...).
It was driven by a Briggs & Stratton 150212-256-B8 Horizontal OHV Engine (250cc 1150 Series 11.5 Gross Torque) (http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200355693_200355693).
Andy Sayler
Tufts Hybrid Racing
Tufts University
Medford, MA
Why would 80 Volts mean less back-flow? Does it have to do with the batteries? Thank you very much for the links.
Owner of a 1973 VW Super Beetle Electric.
The generator turns into a motor when the battery voltage is higher then the generator voltage. Thus having a higher voltage generator tends to lead to less of this problem. Note that a 72V lead acid battery bank will ride at about 76V when charged and can be charged with up to around 85V, depending on the battery type you're using. See here: http://www.batteryuniversity.com/partone-13.htm. An 80V generator is more in this range.
All that said, The correct way to solve this problem is with some controller intelligence, as previously mentioned.
Andy Sayler
Tufts Hybrid Racing
Tufts University
Medford, MA
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
Hi Andy!
I have a 36vdc rail car (dune Buggy) I built last year out of a Yamaha golf cart and a VW bus 4 speed trans-axle. I was making about 30 miles to a charge. My controller is rated 24 to 72vdc. Two months ago we decided to fit a generator. We made our genny out of an old Evinrude Sportwin 10hp outboard engine and a Lemco LEM200-D127 72v PM motor. The genny puts out 42vdc at 70ish amps. Under full load the car draws 160ish amps. We've attached the genny leads directly to the battery terminals. The generator has about a .75 gallon tank. Testing phase is ongoing, but I can report with generator assist, I'm in the 90 mile range.
I run the generator until it's out of fuel and get roughly 15 miles to find fuel/power.
I should say that the pacific northwest has not been kind to the testing process. It's only sunny on the days I have no time. My next test I'll bring a can of fuel and see if the batteries give out before the generator.
I'm not all that technical on the electronics, (more of the mechanic for the project) but we are seeing no adverse effects on the batteries or controller at this time. From what I can tell the motor controller draws the 70amps off the generator first and then looks to the battery bank for extra power. As an added benefit, the generator runs constantly, so I'm charging as I sit at red lights. also I should mention that my motor has two output shafts and I have hooked a 90amp alternator to my aux battery. (This is marginally untested as well)