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Using alternator as starter engine

16403 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.
Yes. I meant in my initial post the internal combustion engine; I edited my post and added "internal combustion" now, so that's clearer.

aside from that I have no idea what you are trying to accomplish,
The other post I did ( ) 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

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.
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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:

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

How much Nm do I need exactly ?

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

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.

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

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.

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
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, ...) ?
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why don't you put the torque wrench ON THE THING YOU ARE TRYING TO START?!?!?
I don't have a torque wrench to measure this.

In any case, I think I overlooked one other important thing: the alternators will be connected on the belt too, and the starter motor will hence drive them as well, so won't that increase the starting power requirements considerably ?

The alternators generate (together) 145 to 155 Amps @ 48V (at a speed of 4000 to 5500 rpm). The torque they generate is:
Pout = torque (τ) * angular velocity (ω)
angular velocity (ω) = rpm * 2π / 60
angular velocity (ω) = rpm * 0,1046
angular velocity (ω) = 4000 * 0,1046
angular velocity (ω) = 418 rad/s
torque (τ) = rpm / ω
torque (τ) = 4000 / 418 rad per second
torque (τ)= 9,56 Nm @ 4000 rpm
At a speed of 5500 rpm, the torque is 9,56 Nm as well.

Rotation speed at starting should be way lower though (say 100 rpm), so needed torque will be 9,56 Nm for each alternator. There are 2 of these, so 19,12 Nm (per minute). In Nm/second that's 0,31 Nm/s. 0,31 Nm/s is about 0,0004 HP Adding that to the 2-3 HP needed to start the internal combustion engine makes 2,0004 to 3,0004 HP that's needed to start the whole thing. So, I'll need to buy a new (5 or 10 HP, 12V) starter motor anyway. The only problem I can see with this solution is that the batteries I'm using may either not be able to power it. A quick calculation seems to confirm this:
5 HP = 3728 watt
3728 watt/12 V= 310, 66 Amp
My batteries only provide 140 Amps, so I can't use these. I could buy a battery specific for this starter, but that battery then won't be able to be recharged.

For 10 HP:
10 HP = 7457 watt
7457 watt/12 V= 621,41 Amp

An alternative I was thinking about is just to keep the current (2-3 HP ?) starter motor and just put in a system that disconnects the alternators (electrically, not mechanically). I heard about such a system being used in recoil start generators, but I'm not sure how it needs to be done. I assume I need to put in a switch, but don't I need to built in the switch before the magnet, so unscrew the entire housing of the alternators for this ?
If this solution could be used, it might solve the battery amperage issue, since I assume it will be able to run on 124 Amp (if 2 HP is enough, if 3 HP is needed, it's too little -186 A-)

I've also been thinking to put in some sort of clutch between the starter motor and the internal combustion motor/alternators assembly. The idea is that I can then disconnect it after starting, avoiding unnecessary power loss. However, which kind of clutch do I best use for this. I'm thinking of having it connect directly to an axle, and have the alternators run on belts from this axle. The question here is: what type of clutch do I best use for this purpose. I prefer to use a cheap, and relatively lightweight type of clutch.
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418Nm @ 4000rpm would give ~ 175kW
575Nm @ 5500rpm would give ~ 331kW.
Obviously you take the relation between torque and angular velocity wrong.
My calculations give around 17.2Nm for a motor that consumes 150A from 48V, that would be if the alternator has the same efficiency as a motor as it has as a generator and that is 100%.
Yes. I made a mistake initially (I switched the torque for angular velocity, and forgot to calculate out the torque from this angular velocity number). I corrected it now in my previous post.

It doesn't really matter though; I'll either use my old starter motor, or buy a new one (that's some 15 HP in power -smaller ones aren't sold here much-). I'll use an AGM battery for it (that won't be recharged initially in the system).

If I buy a new starter motor, it will probably come equipped with a retractible system, and having examined this better, it seems it seems much easier to install than what I initially thought. So, I would then not need any clutch, nor integrate the electrical disconnect function on the alternators.
I'm assuming the AGM battery will be able to provide 930 Amps to it, so that's solved too.
And finally, the question I started off with: will running my alternator in reverse (so as a motor by putting a current on it) damage my alternators is solved too: I'll need to use a starter motor anyway, so whether or not this damages the alternator is of no concern in this project.

The only questions that remain are if I use my old starter motor:
I'll need some sort of clutch. I still don't know what type I best use, so could use some help with this. Also, I'll then need the some guidance on the electrical alternator disconnect method.
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if I understand your ideas and needs correctly, GM has already built this type of vehicle: the Volt (the Holden Volt in Australia and New Zealand, and with a different fascia as the Vauxhall Ampera in the United Kingdom and as the Opel Ampera in the rest of Europe.)
I read the article about the GM Volt. It says that "the Volt operates as a pure battery electric vehicle until its battery capacity drops to a predetermined threshold from full charge. From there its internal combustion engine powers an electric generator to extend the vehicle's range as needed."

That's not at all how my system would work. With the GM Volt (and other cars using a same propulsion system), the battery capacity still needs to be substantial, given that people want to be able to reach most off their (nearby) destinations without needing to using the gasoline engine. The gasoline engine is only used whenever the user needs to go on a trip that is really far away (and can thus not be reached on the battery alone).

It is true that I also put in place a system that falls back on running the electric engine directly off the alternators spun by the internal combustion engine. However, this technique is meant only as a fail-safe. It would be used only when:
* (one of) the batteries break down
* or when the batteries installed have a too low C-rate to be able to be recharged fast enough by the alternators (the alternators hence generate more people than what the batteries can process)

The latter is the case in my demonstration vehicle (kart), simply because there are no batteries on the market that are both so small in capacity, and yet have such a high C-rate.

It goes without saying that in market-ready vehicles (no prototypes), the latter situation should never occur at all. As such, only the main system would be used.

This main system would consist of one (or two) batteries that are constantly recharged by the internal combustion engine. The internal combustion engine is started/stopped depending on whether it needs to charge the battery (or batteries) or not. The internal combustion engine/alternators hereby produces a same amount of power than what can actually be processed by the battery (or batteries).

The idea is that the capacity of the batteries would not be more than the capacity needed to drive say 1 km. So, the batteries are used more like a buffer, and are implemented mainly to allow the vehicle to still obtain the energy consumption advantages the batteries bring.

As we read on the GM Volt FAQ, the battery capacity is with this vehicle still 35 miles (=56 km), so about 56x more capacity than what I intent it to be (and so has a battery cost and weight of the battery that is both 56x higher too). Besides that, -as mentioned-, the system works differently (it works either on the battery -EV mode-, or on the power of the internal combustion engine). My system works on both at the same time.
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What you have conveniently left out of the quote from Wikipedia is the next line: " When the engine is running it may be periodically mechanically linked (by a clutch) to a planetary gear set, and hence the output drive axle, to improve energy efficiency"
So, YES the electric motor and the ICE CAN and DO run at the same time in the Volt.
I looked into the GM Voltec powertrain and examined the details.
The system is still different, despite that electric motor and ICE can indeed run at the same time. The difference lies in the fact that my system (when in the "fail safe mode") just uses the electricity generated from the internal combustion engine's alternators to power the electric engine whereas the GM Volt either:
* mechanically links the internal combustion engine to the axle on which the wheels are mounted
* or use the internal combustion engine to generate electricity with so as to recharge the battery with this
For that last one, it even does this only to keep the battery at the minimum charge level (30% of capacity). So it won't charge the battery fully (to 90 or 100%).

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.
I looked into the Toyota Prius as well.
The Toyota Prius is a parallel hybrid, not a series hybrid (as my system).
I do read that it indeed has a very small capacity battery (which allows but 1 mile to be driven with it). Yet as its a parallel hybrid system, it works differently from my system. Lastly, I even doubt whether the battery can be recharged (about) as fast as it is discharged (operating the electric engine at normal speeds), given that it has a NiMH battery. That latter is what I refer to with my term "quickly rechargeable energy storage system".
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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?!?!
I never wanted to give the impression that I have any practical experience with electric cars or hybrid cars for that matter.

I just examined the HSD schematic over at wikipedia, and it seemed to me that there is a mechanical linkage between the ICE, and MG1 and MG2 (and both MG1 and MG2 can act as electric motor and alternator). The drivetrain explaination then mentioned that there are 2 hybrid modes (Eco and Power) so it can indeed run in series hybrid mode. That said, the internal combustion engine (ICE) still does have a mechanical linkage (it's not just electrically connected to MG2 -which acts as the main electrical motor I read-). So, if it is mechanically linked, who says the vehicle does not run only on the ICE at some points (say when the traction battery does get completely discharged, despite that it could -in theory- be recharged as fast as it is discharged ?
I'm not fully convinced of the latter, and even if it never runs only on the ICE, I still think it differs from my system, just because I have no such mechanical linkage anywhere in my system.
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You see initially GM had the Volt set up just as you describe your set-up with no mechanical link between the ICE and drive wheels. They quickly realized that in important driving situations such as hard acceleration, sustained freeway driving, low battery state, and others there was a distinct power and efficiency advantage to having a direct mechanical link between the ICE and the drive wheels.
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.
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.
I hear both your comments on series hybrids, but still see value in a very simple (pure) series hybrid system. This as:
* it is simpler and cheaper to repair when broken down and replacement parts are easier to obtain (since they don't need to be very specific)
* it is much cheaper to make
* they still offer energy consumption benefits over regular (non-hybrid) vehicles, especially when used in situations with a lot of traffick (a lot of starting/stopping) -they will be less efficient than parallell hybrids or complex hybrids like the Prius/GM Volt but that's a trade-off with the other benefits mentioned here-

I just want to try it out and see whether I can't make this work, and create a vehicle with the above benefits. If it won't work, I'll also accept this (the reason I'm doing this is to create environmental benefit, not to gain huge financial rewards). So if it doesn't provide that, I would just scrap the idea and focus on either changing the project or focusing on something else.

As far as charging the batteries at a high rate and providing power to an electric motor at the drive wheels: there's no free lunch here. To do both and maintain normal driving abilities of the car (i.e. good acceleration and freeway speeds) you would have to have a more powerful, more gas guzzling ICE. This totally defeats the purpose of trying to increase efficiency and reduce gas consumption!
I'm not trying to:
* charge the batteries (which aren't used right away)
* and drive the electric motor straight from the ICE

I'm trying to charge the batteries -which ARE used right away-
OR drive the electric motor straight from the ICE (= fail safe)

Also, increasing efficiency and reducing gas consumption isn't my only motivation on doing this. The point really is about making a propulsion system that makes road transportation more ecologic. That goes beyond just increasing efficiency and reducing energy consumption. For instance, if compared to a fossil-fuel powered (non hybrid) vehicle, my hybrid system is used whereby a biofuel is burned in the ICE, and the components of my hybrid system are easily recyclable -and there's very little or sometimes even no efficiency gain-, then I allready consider this an ecological merit, so a success. There are many other possible eco-gains that could come out from my project as well. I'll just keep tweaking things and look at the outcomes.

Anyway, there's little point in keeping to discuss the theory of my drivetrain; rather I need to build it, so it's better to skip ahead to my other post.
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