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Old 02-10-2017, 07:07 AM
electric_driver electric_driver is offline
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Lightbulb Using alternator as starter engine

Hi,

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
http://www.prestolite.com/productinf...09ZA_curve.jpg

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):
http://cs-shop.de/LiFePo4-Motorrad-S...ler-bis-350ccm

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.

Last edited by electric_driver; 02-15-2017 at 08:02 AM.
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  #2  
Old 02-10-2017, 07:43 AM
dcb dcb is online now
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Default Re: Using alternator as starter engine

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?
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Old 02-11-2017, 01:17 AM
electric_driver electric_driver is offline
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Default Re: Using alternator as starter engine

Quote:
Originally Posted by dcb View Post
fyi we call electric engines motors. engine typically implies a gas or diesel engine in this context.
Yes. I meant in my initial post the internal combustion engine; I edited my post and added "internal combustion" now, so that's clearer.

Quote:
Originally Posted by dcb View Post
aside from that I have no idea what you are trying to accomplish,
The other post I did (http://www.diyelectriccar.com/forums...d.php?t=181433 ) were questions relating to the electric engine for my project (the whole (electric engine + alternators + internal combustion engine) would be used in a hybrid kart; see http://hybridkart.altervista.org/)

Quote:
Originally Posted by dcb View Post
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?
I doubt I need to calculate out the torque ? Also, I don't want to spin it at 6000 rpm. The maximum would be 4000 to 5500 rpm, but that's even for regular running (not starting). I would run it at the lowest possible rpm for starting. I was thinking of say giving it 5 amps at 48V, hence allowing it to spin briefly at 2000 rpm for starting. I could go even lower, say 1 amp or so.

The main question I have is whether doing this wouldn't damage the alternators. I don't know what type of alternator I have (claw-pole, ...) and whether it is as such suitable for use as a starter.

Last edited by electric_driver; 02-11-2017 at 01:24 AM.
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  #4  
Old 02-11-2017, 03:08 AM
Duncan Duncan is offline
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Default Re: Using alternator as starter engine

I could be wrong but I would be absolutely amazed if an alternator would have enough torque to turn a stationary engine

There is absolutely no need for anything like that much torque in its normal operation

A starter motor uses hundreds of amps - an alternator is wired for tens of amps
And more importantly a starter motor is geared down massively - 40:1 at a guess

So at a first approximation an alternator will have about 1/100th the required torque
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Old 02-11-2017, 03:44 AM
electric_driver electric_driver is offline
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Default Re: Using alternator as starter engine

Quote:
Originally Posted by Duncan View Post
I could be wrong but I would be absolutely amazed if an alternator would have enough torque to turn a stationary engine
Ok, some calculations for the alternators then:

Power
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-

Torque
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

How much Nm do I need exactly ?

Quote:
Originally Posted by Duncan View Post
a starter motor is geared down massively - 40:1 at a guess
So at a first approximation an alternator will have about 1/100th the required torque
I don't know how to resolve this issue; to run in "normal mode", it would be connected with the 65/40 or 65/55 gearing. I can't use 1/40 gearing.
From what I've been told, alternators are nonetheless used for this starting purpose too, in hybrid vehicles. So, if the gearing is an issue, how do the manufacturers of hybrid vehicles solve that ?
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Old 02-11-2017, 04:51 AM
Duncan Duncan is offline
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Default Re: Using alternator as starter engine

Hybrid systems using the alternator have a muckle great alternator - and don't drive it though a dinky wee belt!

As to how much torque it will take to start your motor - remember the old days of starter handles?
They would have a lever of maybe 9 inches and would take at least 100lbs force

So 75 Ft lbs = about 114 Nm

Your motor is smaller - but also higher compression
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Old 02-11-2017, 06:25 AM
piotrsko piotrsko is offline
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Default Re: Using alternator as starter engine

Ok I must be missing the obvious here.

Why cant you use the drive motor to start?

It has been my experience that you need 1 -2 hp for starter motors at about 100 rpm to put enough energy into the flywheel to overcome compression
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Old 02-11-2017, 06:38 AM
dcb dcb is online now
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Default Re: Using alternator as starter engine

Quote:
Originally Posted by electric_driver View Post
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).

Quote:
Originally Posted by electric_driver View Post
Ok, some calculations for the alternators then:

Power
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-

Torque
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.
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Old 02-12-2017, 03:37 AM
electric_driver electric_driver is offline
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Default Re: Using alternator as starter engine

Ok, first for this post (which bugged me):

Quote:
Originally Posted by dcb View Post
And that you wish to patent THE SIZE OF THE BATTERY IN PRIOR ART!?!? go screw your self for that actually.
I didn't patent it for any financial rewards. Rather, I patented it out of ecological reasons. More precisely, it was an idea I had which I felt would be soon discovered by (commercial) companies and might be patented by them. Once patented, they could then even block the idea of being used by anyone.
So although I could have chosen not to patent the idea at all, that's not how things work and if I wouldn't have, it would (or could) have resulted in environmental damage.
I intent to make the idea available to as many commercial companies as possible, under my own terms (which aren't dictated by commerce but by ecology).
In any case, my patent would only affect companies, I don't intent to sue private people (hobby builders) that would use the system I patented.

Quote:
Originally Posted by dcb View Post
Why don't you stick a torque wrench on something and find out?!? Or at least get an approximation (worry about drag later).
I don't know the brand of the starter motor I have (which works to start the internal combustion motor). That said, it is powered by a Rocket 30-12 battery. That battery delivers 12 V and the amperage is:
under 13,8 V: unlimited amps
from 14,4 V and up: 7,5 Amps maximum

Quote:
Originally Posted by piotrsko View Post
Why cant you use the drive motor to start?
So you mean the electric motor ? This motor is connected to the wheels (drive shaft), and not to the internal combustion engine, so that won't work.

Quote:
Originally Posted by Duncan View Post
As to how much torque it will take to start your motor - remember the old days of starter handles?
They would have a lever of maybe 9 inches and would take at least 100lbs force
So 75 Ft lbs = about 114 Nm
Quote:
Originally Posted by piotrsko View Post
It has been my experience that you need 1 -2 hp for starter motors at about 100 rpm to put enough energy into the flywheel to overcome compression
So, I gather that the alternators do have enough power overall, but they just don't have the right gear ratio in order to have enough power to start the internal combustion engine.

There are 3 options I can see to overcome this:
- either use one of the alternators only as starter motor, and change the gear ratio of it.
- or buy a different starter motor that is capable of handling the high rpm and add that to the toothed belt assembly (by means of a disc with the correct gear ratio)
- or change the assembly so the starter motor can be disconnected, but using another way (using a clutch)

I prefer option #2 and #3 of these, since I didn't bought an internal combustion engine with 17-20 HP to then just use it at 30% or so of its power output, and also didn't buy an expensive alternator to then use it as a mere starter motor.

If I use option #2, what brands/models of starter motor exist that can handle this high an rpm ?
Also, the brand/model chosen would best be able to run on one of the battery packs I'll assemble (so the battery would supply 12 Volt @ 140A). The idea I have is to have the system select whichever of the 2 12V, 140A battery packs which is currently still fully charged (the battery packs are charged/used intermittently). The alternative is to use a standard battery (normally used with the starter motor) but the downside is that this battery would then not be recharged (unless the starter motor too can act as an alternator, but that would complicate matters, and probably isn't easy to get a hold of).

If a rectractible starter motor is really needed, how do I best set this up (can I combine gears with a toothed belt drive, ...) ?

Last edited by electric_driver; 02-13-2017 at 02:58 AM.
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  #10  
Old 02-12-2017, 06:53 AM
dcb dcb is online now
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Default Re: Using alternator as starter engine

Quote:
Originally Posted by electric_driver View Post
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..
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