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Using alternator as starter engine

16363 Views 26 Replies 9 Participants Last post by  jared2009gregg

I'm building a hybrid vehicle, and for this I need to use (one of) the alternators attached to my internal combustion engine as a starter engine. My initial idea was to just use a starter motor, but since I can't use the retract function of this, it needs the starter engine to remain connected all the time, and (besides that this lower efficiency), it would also rip the starter engine apart due to the sheer force when running at full speed. So obviously I need to use one of the alternators as the starter motor.

The internal combustion engine I'm using is a 17 - 20 HP internal combustion engine. It runs at between 6000 - 7000 rpm (say 6500 rpm)
The most efficient rpm for the alternators (regular running, NOT starting !) is between 4000 rpm and 5500 rpm. So, I'll be using a 65/40 or 65/55 gearing in between the internal combustion engine and the alternators. I'll be using not gears, but a toothed belt for this, probably in a V-type setup.

The alternators are 2 Leece-Neville 8SC3009ZA's (well actually Prestolites, but these have the same specs as the Leece-Nevilles). They run at 24 Volt (output of the 2 is hence 48 V). Power curves are at

The batteries the alternators charge will probably be 4 batteries of 12 Volt (with 2,3Ah), in specific, these ones (as they're quickly rechargable):

I'll actually be using 2 sets of 4 batteries, so as to allow running the engine from 1 set, while charging the other set of batteries.

Anyway, the question I have is: won't this damage my alternators (as they're not intented to be run as engines, and I'll be starting (and stopping) the engine a lot), and is the power of the batteries (140 A @ 48 V) sufficient ? I assume so, from the power curve, but I still like to hear a second opinion, and hear that it is indeed possible to run these alternators as engines without damaging them.

If the above won't work, will some other batteries from cs-shop (in particular the 150A @ 12V, with 2,5Ah) be able to do it, and/or do I need still other batteries.

Note that the batteries have so little Ah mainly because I like to keep the vehicle very lightweight.
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fyi we call electric engines motors. engine typically implies a gas or diesel engine in this context.

aside from that I have no idea what you are trying to accomplish, these problems have been solved a hundred times already, and of course you haven't given us nearly enough information to answer any sort of questions.

I was going to say you might be able to guesstimate the alternator as motor torque based on the graph, but it doesn't even go below 2000 rpm for some reason, which makes me wonder what kind of starter (from 0 rpm) it would make.

but lets assume the graph as alternator is roughly the same as motor once it is spinning.
so just to test your understanding (and assuming %100 efficiency), what is the torque being put into the alternator if it is making 24 volts and 170 amps at 6000 rpm?
How much Nm do I need exactly ?
Why don't you stick a torque wrench on something and find out?!? Or at least get an approximation (worry about drag later).

Ok, some calculations for the alternators then:

1 Amp @ 48 V = 48 watt (0,048 kW) -speed is then about 2000 rpm-
5 Amps @ 48 V = 240 watts (0,24 kW) -speed is then about 2000 rpm-
140 amps @ 48 V = 6720 watts (6,7 kW) -speed is then about 3800 rpm-

0,048 kW @ 2000 rpm gives 0,23 Nm
0,24 kW @ 2000 rpm gives 1,15 Nm
6,7 kW @ 3800 rpm gives 16,84 Nm
Like I said in the other thread. Torque is directly related to motor amps, and rpm is directly related to motor volts. Note you can *probably* overamp a motor for more startup torque.

but I read the patent stuff and I have zero interest in explaining all the misconceptions in play here, especially since you don't seem to be listening.

And that you wish to patent THE SIZE OF THE BATTERY IN PRIOR ART!?!? go screw your self for that actually.
i don't know the brand of the starter motor i have (which works to start the internal combustion motor).
why don't you put the torque wrench ON THE THING YOU ARE TRYING TO START?!?!?

Jesus f-ing christ..
my prius only goes about a mile on electric. It has a very small capacity battery by comparison, most hybrids do. This is not some new or even groundbreaking idea, and the Prius has had probably hundreds of thousands of development hours behind it to make it reasonably efficient. It has a motor/generator connected to the engine (that doubles as a starter) and one connected to the wheels.

Oh, and the batteries are augmented by the engine for higher power demands.

The Toyota Prius is a parallel hybrid, not a series hybrid (as my system).
You don't know what you are talking about. It has a powersplit, at various times all the torque goes to the wheels, or to the generator, or both. from the generator it goes to the wheel motor and/or the battery. Why does it have a motor generator on the engine and one on the wheels if it couldn't series?!?!

You don't look very hard and you listen even worse, but you assert like you know what you are saying.

Lastly, I even doubt whether the battery can be recharged (about) as fast as it is discharged
They use it to stop the car. I'd say it can be recharged pretty quick. According to these guys it EXACTLY can be recharged as fast as it is discharged (it is a low energy/high power form of nimh).
I still think it differs from my system, just because I have no such mechanical linkage anywhere in my system.
I guess the problem is that "your system" isn't your system, the very first hybrids were people putting generators on their electric vehicles. It is literally the most simplistic way to make a "hybrid". But like a few people have tried to tell you, with all the conversion losses it is rather inefficient. Your focus seems to be on trying to put lipstick on that pig, because you invested a lot of time/money before really understanding it. Build a bridge and get over it.

the Prius allowed it to mix in parallel because it is more efficient than "pure" series all the time.

With all the conversion losses series is about the worst. It matters not if your engine is at peak bfsc if you lose %40 getting it to the wheels.

Besides the prius engine runs in atkinson mode (they increase the expansion ratio via valve timing), it is more load sensitive than rpm sensitive. And mg1/mg2 can do whatever they need to. You essentially get an "electric" continuously variable transmission w/overdrive. With a small battery to help accelerate and reclaim braking energy, and allow the engine to shut down completely when not needed (and also which provides instant 1000 rpm engine starts that reduce emissions, as apposed to a 2hp bump and chug start).

There was a team in the automotive x-prize that attempted a series hybrid, hoping to sync the motor and engine up magnetically, but it doesn't sound like it would work well except under very specific operating conditions. With power split (prius/volt) you get the best of both worlds. I would study the prius power split device first, volt would have gladly used it if it weren't for patent issues (AHEM!!), but they had to change it a bit to make it look different.
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