Replacing an alternator with a brush-less motor

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modern_messiah   100 W

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Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 06 2012 8:00am

Ok,

I've been out for a little while so my memory is a tad foggy, and please forgive me if this is either the wrong place to discuss this, just a stupid question, or probably both. Hopefully it hasn't been covered before though given the very inquisitive minds on these forums it's entirely possible!

Ignoring whether or not it's worth it from a performance and cost perspective, could you theoretically replace the alternator in a car with a brush-less motor (plus required BMS and controller) and end up with a system that not only charges your battery but can also work in the opposite sense and add more power to your drive train? Obviously I don't mean do both at the same time - charge when breaking or cruising and discharge when accelerating hard (or something along those lines)?

It clearly wouldn't be a straight swap (new mounts, places to store various parts, possibly needing to strengthen or replace the belt and so on) but would it not be technically possible?

Yes I've thought about this for all of 2 seconds. I may or may not just be bored right now...maybe some sleep would help ;)

- Matt

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Re: Replacing an alternator with a brush-less motor

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Re: Replacing an alternator with a brush-less motor

Post by thegrizz » Sep 06 2012 10:14am

modern_messiah wrote: end up with a system that not only charges your battery but can also work in the opposite sense and add more power to your drive train?
the alternator serves as a inline charging system for the battery while the engine is operating - nothing more.
Is there a possibility of swapping out a standard alternator for a BLDC motor with the hopes of reducing the engine forces required to generate power - yes.
Will this reduction in engine output (specifically for the alternator) have an effect on engine performance - probably not noticeable. Contrary to what you may think, standard auto alternators have very little drag - maybe pull 1-2HP under normal operation.

you made me think of something while I was typing this though - it would be a good DIY....

What if you add a secondary alternator - maybe even a BLDC - to generate power to a auxiliary accessory or power source. There may be benefits with this and if your secondary charging rig fails your not stuck out in the middle of the outback cursing the day you decided to replace your stock alternator with a hub motor.

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Re: Replacing an alternator with a brush-less motor

Post by thegrizz » Sep 06 2012 10:16am

Awesome. I've never seen one pulled apart.

great link.

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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 06 2012 4:14pm

Volton Bicycles wrote:
modern_messiah wrote: end up with a system that not only charges your battery but can also work in the opposite sense and add more power to your drive train?
the alternator serves as a inline charging system for the battery while the engine is operating - nothing more.
Is there a possibility of swapping out a standard alternator for a BLDC motor with the hopes of reducing the engine forces required to generate power - yes.
Will this reduction in engine output (specifically for the alternator) have an effect on engine performance - probably not noticeable. Contrary to what you may think, standard auto alternators have very little drag - maybe pull 1-2HP under normal operation.
I might be failing to get the point here (so apologies if this is the case) but if you use a reasonably powerful BLDC motor you can have it set up so that you possibly charge 2 batteries - the car's regular 12V battery, and the a High Power LiPo pack stored elsewhere. the BLDC motor can charge both packs (some trickiness needed but definitely doable) as a regular alternator and then when the time comes and the motor is operated as a motor it would take load off the engine. I know the alternator is just an inline charger, but in a typical setup its 'sucking' power from the engine to spin itself. If you give it enough power it takes it's own load off the motor. Give it MORE power and it not only unloads itself but also adds more torque and power to the rotation of the crankshaft, meaning the engine turns over more easily. Yes we're not talking about big power here but with a big hobby grade BLDC motor it could mean an extra 20HP.

Pie in the sky stuff I guess.

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Re: Replacing an alternator with a brush-less motor

Post by thegrizz » Sep 06 2012 7:08pm

If you give it enough power it takes it's own load off the motor. Give it MORE power and it not only unloads itself but also adds more torque and power to the rotation of the crankshaft, meaning the engine turns over more easily.
I'm by no means a master of mechanical or electrical engineering but know that an alternator only functions under load - at least a standard delco alternator. With no load present the alternator, for sake of argument, is a freewheeling motor with a cog tied in via tension belts to the crank. The alternator, which is technically a motor, doesn't add power back to the crank - alternators supply voltage back to the battery, or a LiPo pack if you will, while running at over 2x crank speed.

A (of alternator) x V(14.9) = W
W/ HP (1HP=745.5W) = electrical output of alternator in HP
add some inefficiency loss = roughly how much load your alternator is putting on the main engine

There is engine load - the power needed to power auxiliary systems, motors, transmission via belts and gears; and there is electrical load - or power consumed within a circuit

I'm a little confused by "motor is operated as a motor" line....
Are you talking about the potential of removing the "alternator" (whether stock or bldc) from the belt system of the engine and instead using an externally controlled BLDC motor to charge the battery or batteries?
Are you saying you can reach a degree of rotation where the bldc motor can self excite with out the control of an external source? which i think is possible....

Either way, I think you have the right idea.

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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 06 2012 8:05pm

We might have some wires crossed here (pun not able to be avoided haha).

I've sat down and drawn some doodles and have come to a very basic understanding of what would be needed. I might research a bit more and if I think it's doable I'm going to try it. You basically need a typical e-bike setup. You could keep it simple by not automating alternator/motor phase of the BLDC (so it's always acting as an alternator until you press a button) and not automating the recharging of the LiPo pack (so you need to manually charge it after each drive). Once that's working then the system could be upgraded to be 'smarter'.

Care would need to be taken to ensure that charging of the car's battery is not neglected. Plenty to think about anyway.

- Matt

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Re: Replacing an alternator with a brush-less motor

Post by amberwolf » Sep 06 2012 8:45pm

There is already a car that has an "alternator-starter" or something like that, possibly BMW, where the alternator is also used as a motor to start the engine; in theory it could be used to add some drive to an engine, but I don't know what the consequences would be.

There have been discussions about it here on ES and over on DIY Electric Car forums.

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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 06 2012 10:02pm

Thanks amberwolf....I have tried looking because I'm certain it's nothing new but the right search terms are really, really difficult to get right :(

In theory it's actually quite simple, and the more I think about it the simpler it gets. The only thing tripping me up is how the control of the BLDC motor would be handled - I need to read back up on my motor theory, its been way too long. When you open up the throttle down on an electric motor you want to increase the voltage to the motorand this controls your speed. The controller pulls more current to help achieve the desired voltage (why you pull more current up hill and less down hill) and hence speed. But if your speed in the BLDC motor is effectively capped (dictated by the RPM of the car engine) then what happens? In this particular instance you want maximum current going to the motor and any RPM (for maximum power) so you want to increase the current without increasing the voltage (unless the RPM of the motor needs to increase).

I'm blabbing. I don't actually have a clue what I'm talking about. It's on my brain but I just can't articulate it. I need to research more :?

EDIT: The sort of technical term for this is BAS(Belted Alternator Starter) and was developed by GM. Basically exactly what I want to do except I have no intention of replacing the starter motor - so my system would be purely for performance gains (regardless of how little haha).

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Re: Replacing an alternator with a brush-less motor

Post by dkw12002 » Sep 09 2012 9:24am

If you did that you would have a Prius.

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Re: Replacing an alternator with a brush-less motor

Post by spinningmagnets » Sep 09 2012 10:00am

In the Navy I have seen Motor-Generators (MG's), but...we were short on space and had a blank check (submarine had an enormous FLA-DC battery).

I have seen a you-tube where a guy added a second large Leece-Neville alternator (from an 18-wheeler, 130A?) under the hood (a truck with engine bay space?), and it was converted to a 24V motor that he used as a hybrid motor to help acceleration (In a 2-ton vehicle) and reduce fuel consumption (in a vehicle shaped like a brick). It "sort of" worked, but didn't seem worth the effort required.

There is lots of info on the web about making an alt into a motor (I've never done it). Some of the best alternator tutorials are about how to externally regulate one to make it a road-side welder (from 4X4 sites), put the Jeep in neutral, rev the motor, and weld away with jumper cables... http://forums.off-road.com/jeep-short-w ... aight.html

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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 09 2012 4:03pm

spinningmagnets wrote:In the Navy I have seen Motor-Generators (MG's), but...we were short on space and had a blank check (submarine had an enormous FLA-DC battery).

I have seen a you-tube where a guy added a second large Leece-Neville alternator (from an 18-wheeler, 130A?) under the hood (a truck with engine bay space?), and it was converted to a 24V motor that he used as a hybrid motor to help acceleration (In a 2-ton vehicle) and reduce fuel consumption (in a vehicle shaped like a brick). It "sort of" worked, but didn't seem worth the effort required.

There is lots of info on the web about making an alt into a motor (I've never done it). Some of the best alternator tutorials are about how to externally regulate one to make it a road-side welder (from 4X4 sites), put the Jeep in neutral, rev the motor, and weld away with jumper cables... http://forums.off-road.com/jeep-short-w ... aight.html
I startec converting a 24V truck alternator to a motor about 12 months ago but gave the idea up because it just wasn't worth the effort. Was an excellent learning curve though. Just better to buy something designed specifically for the purpose at the moment. I'm thinking of leaving the alternator be and just adding in a second motor because not only have I found a nice big open space under my bonnet, but I've also found a very easy way to get power to the crank pulley (basically a custom crank pulley with a chain drive on the end. minimal welding to install the motor mount.

It'll be a long road but even over the 2 days of the weekend just gone I've got a much better picture of where I'm headed.

...and yes it'd be like a prius. In the same way the 911 GT3 Hybrid is :twisted:

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Re: Replacing an alternator with a brush-less motor

Post by tostino » Sep 10 2012 2:50pm

That was actually the exact same idea I had come up with for my 96 Corolla. I was wanting to leave the existing alternator in tact, and just add an additional motor + pulley to help with acceleration. I was planning on using one of the 36 fet infinion's i'm building up for it (and the other one on my mountain bike).

I'd just have a CA or something in the car to measure the AH usage, and use it as a plug in hybrid performance mod.

Wasn't planning on starting it too soon though, because I wanted to get my bike done first. I'll be interested to see what you come up with!

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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 10 2012 5:39pm

tostino wrote:That was actually the exact same idea I had come up with for my 96 Corolla. I was wanting to leave the existing alternator in tact, and just add an additional motor + pulley to help with acceleration. I was planning on using one of the 36 fet infinion's i'm building up for it (and the other one on my mountain bike).

I'd just have a CA or something in the car to measure the AH usage, and use it as a plug in hybrid performance mod.

Wasn't planning on starting it too soon though, because I wanted to get my bike done first. I'll be interested to see what you come up with!
Yep - I've decided that while replacing the alternator would be the cleanest and most integrated solution, it is a LOT of mucking around. so much in fact that it's not worth it, especially in my car which is a 2009 Subaru Legacy - it's too new for me to be changing that much stuff around. Leaving the ancillary system as is, and adding a motor elsewhere is the best solution I can think of. There’s also a tonne of room where I want to put the new motor as its right next to the stock battery which can be moved if need be.

A few things I’m hung up on at the moment are:

- what motor to use: 1 large motor like a colossus/RotoMax 150 or 2/3 smaller motor geared together. My preference is to use the higher quality gear like some of the custom motors people are designing and testing in these forums. The problem is these motors either seem to become available rarely or have massive problems being controlled – you only need to look at the Colossus thread to see how difficult it is. Seems like way too much effort! Then there is that 14km Astro rebuild (can’t find the thread) that looks amazing but have we got a controller that can run it?! Getting a motor with a high enough kv is also a problem. A 1:1 gearing between the BLDC and the ICE means the BLDC needs to be capabale of 6,500rpm at least. Gearing it down (for more torque) means a higher kv is needed again.

- as already rambled about what controller to use (completely dependant on motor choice of course).

- whether to have the motor permanently attached to the drive train so regen breaking can be used to recharge the LiPo pack or leave the whole system so that it needs to be charged by an external charger each time it goes flat. Leaving it permanently attached will rob the engine of 1-2hp all the time. That being said if it’s locked to the ICE rotation it can be controlled without sensors because once the engine is idling the motor is already spinning at 1,500rpm.

Controlling it should be simple but I am yet to get a clear answer solution to this. Because the BLDC’s RPM is locked in to the ICE RPM, you simply tell the BLDC motor to go as fast as it can. Because it can’t physically spin faster than the ICE it will draw max current to try and do so….it’ll work its nuts off. To stop it burning out you just limit the current available to it and make sure you cool it really well.

I’m probably talking out my bum though.
Last edited by modern_messiah on Sep 11 2012 5:35pm, edited 1 time in total.

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Re: Replacing an alternator with a brush-less motor

Post by tostino » Sep 11 2012 8:09am

I really have no idea what motor i'd go for, but I was planning on putting a thumb throttle type device on my steering wheel.

It doesn't have to be all or nothing. This will hopefully increase power greatly, and also increase mpg if I so chose to use it for efficiency instead doing 10x more hard starts than I would have normally lol.

Just using a adequate BLDC motor + controller should be fine. Don't think of the motor as "locked to the ICE", just think of the ICE as a load like any other. Yes, it is a good idea to keep the motor + controller cool, but the same is true in any setup.

In my mind, there is nothing that makes this inherently harder on a controller or motor than any other task (as long as you isolate them from the heat of the ICE as much as possible).

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Re: Replacing an alternator with a brush-less motor

Post by Hillhater » Sep 11 2012 6:35pm

...what motor to use: 1 large motor like a colossus/RotoMax 150 or 2/3 smaller motor geared together.
considering you have a 120+Kw ICE, i wouldnt think it was worth considering anything less than a 30+kW E assist drive.
Less than a 25% boost will be difficult to notice.
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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 11 2012 6:44pm

Hillhater wrote:
...what motor to use: 1 large motor like a colossus/RotoMax 150 or 2/3 smaller motor geared together.
considering you have a 120+Kw ICE, i wouldnt think it was worth considering anything less than a 30+kW E assist drive.
Less than a 25% boost will be difficult to notice.
True....I guess low down torque is the bigger advantage, though again this wouldn't be much. I was thinking along the lines of multiple motors. Either way - I still have A LOT of research to do :?

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Re: Replacing an alternator with a brush-less motor

Post by tostino » Sep 11 2012 8:41pm

And on that note, the little 75kw (at it's very best) ICE my car has could see a noticeable increase with quite a bit less power.

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Re: Replacing an alternator with a brush-less motor

Post by modern_messiah » Sep 11 2012 10:37pm

tostino wrote:And on that note, the little 75kw (at it's very best) ICE my car has could see a noticeable increase with quite a bit less power.
A small car like a Carolla with a ICE/BLDC motor combo would be an absolute blast to drive. Imagine if you had an old Turbo Golf or something? I'm seriously considering selling my Liberty and buying a car more appropriate for driving to and from work, and then buying a small project car (like the Golf) and going nuts on it.

Could be fun :P

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Re: Replacing an alternator with a brush-less motor

Post by peterr88 » Sep 18 2012 11:39am

Awesome. I've never seen one pulled apart
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