DC motor, higher voltage just on start...

[supak111]

Hey everyone, got a problem on my car, many other owners have the same issue on this particulate car. There is a VERY EXPENSIVE hydraulic pump that controls the clutch, pump with labor costs $3-4k no joke. The DC motor (12V ~35A) that makes the hydraulic pressure is know to go bad, (I THINK) brushes or commutator usually get dirty because the motor draws ~35A causing higher resistance.

I want to add higher voltage to the motor only on startup say first 2 second... Hoping to overcome higher resistance and get the motor spinning and making hydraulic pressure again.

I was thinking adding a capacitor in series, maybe charge the cap in parallel and discharge it in series, but wouldn't the current stop all together when the cap discharges?

Not sure how I would implement a cap into this circuit to make this happen. Any help much MUCH appreciate. This would help a lot of people on another car forum.


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[Gryd3]

Hey everyone, got a problem on my car, many other owners have the same issue on this particulate car. There is a VERY EXPENSIVE hydraulic pump that controls the clutch, pump with labor costs $3-4k no joke. The DC motor (12V ~35A) that makes the hydraulic pressure is know to go bad, (I THINK) brushes or commutator usually get dirty because the motor draws ~35A causing higher resistance.

I want to add higher voltage to the motor only on startup say first 2 second... Hoping to overcome higher resistance and get the motor spinning and making hydraulic pressure again.

I was thinking adding a capacitor in series, maybe charge the cap in parallel and discharge it in series, but wouldn't the current stop all together when the cap discharges?

Not sure how I would implement a cap into this circuit to make this happen. Any help much MUCH appreciate. This would help a lot of people on another car forum.


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Startup current for Electric motors is expected to be much higher than the running current.
That being said... giving a motor higher than expected voltage to *start* will increase the current draw at startup, and drastically increase the amount of heat/power generated.
You will most likely end up killing the motor sooner with this trick.

I'm unsure what others would suggest, but I would like to encourage you to 'reduce' the inrush current so the motor starts more gentle which should increase it's longevity...

 

[supak111]

Yes but the motor is already not working, I am looking for a way to give it more watts to get it to move. I can't make anything worse here, only better. When this motor dies people with this issue are looking at a $3000-$4000 bill from the dealership. If this trick works than great, if not than I didn't lose anything nor make anything worse. I would only be doing this when the motor is refusing to work. Even if this trick can extend the motors life for another 5000 miles its better than nothing.

That being said, the motor is turned on by a 40amp relay, and there is a 40amp fuse inline so that means even the starting current of this motor isn't more than 40amps max.


I know the higher voltage will give it more current more watts so more heat but I'm looking to do this only momentarily with a proper size capacitor. With just normal driving this motor only runs ON every so ofter for about 6 seconds, it has a LOT of time in down time in between to cool off.

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[Minder]

As has been suggested, you are probably going to cause more grief that way.
In any case a series cap would not supply the current demand as it is.
What I imagine is happening is the hydraulic pump is starting with a higher than normal initial current condition caused by immediate pump pressure, most systems such as this will have an unloading valve that allows the pump to come up to maximum rpm before applying load, IOW a slight delay holds a relief valve off.
Whether or not some after market mod can be done would depend on the system, but I imagine it is doable.
Also if a failed unit was available, it may be possible to find the cause be dismantling the motor for an autopsy !
M..

 

[Gryd3]

Yes but the motor is already not working, I am looking for a way to give it more watts to get it to move. I can't make anything worse here, only better. When this motor dies people with this issue are looking at a $3000-$4000 bill from the dealership. If this trick works than great, if not than I didn't lose anything nor make anything worse. I would only be doing this when the motor is refusing to work. Even if this trick can extend the motors life for another 5000 miles its better than nothing.

That being said, the motor is turned on by a 40amp relay, and there is a 40amp fuse inline so that means even the starting current of this motor isn't more than 40amps max.


I know the higher voltage will give it more current more watts so more heat but I'm looking to do this only momentarily with a proper size capacitor. With just normal driving this motor only runs ON every so ofter for about 6 seconds, it has a LOT of time in down time in between to cool off.

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If you have a 40A Relay and 40A fuse, then increasing the voltage by anymore than 30% will pop the fuse or damage the relay.
You could potentially use capacitors to store a charge then change the circuit and dump them in series with the motor, but you will require a custom circuit to do so. *if* it works, I would be surprised to see you get any more than 1-2 uses out of it, let alone 5000 miles.

I honestly think you best bet if you want a 'DIY' style fix/hack is to go to a wrecker and buy one. It may not be fully functional but you would be free to disassemble it to attempt a repair / hack without risking your current 'failing' motor.
If you can crack the thing apart and simply clean it or swap out a couple minor parts to make it fully functional then you have saved yourself a lot of money in parts depending on the cost you get from a wrecker.
What kind of labour is involved in getting to this motor anyway?

 

[supak111]

Used WORKING pumps sell for $700-1000 thats with 50-80k miles on it, but pumps are known to die from 60-110k so getting a used pump is pointless, big wast of money since it cold die next day after you install it.

The whole pump/motor is install in a really horrible spot on the car, lot of labor hours. + to remove it you have to remove all the hydraulic lines. If you remove the the hydraulic line you have to bleed the system later which only dealerships can do because it requires special software, which means an expensive tow and labor bill from BMW even if you're lucky to fix the pump yourself.

I have found someone was able to remove the motor from the pump without disconnecting any of the hydraulic lines so I might be able to remote it and disable the motor and work on it alone

 

[supak111]

Used WORKING pumps sell for $700-1000 thats with 50-80k miles on it, but pumps are known to die from 60-110k so getting a used pump is pointless, big wast of money since it cold die next day after you install it.

The whole pump/motor is install in a really horrible spot on the car, lot of labor hours. + to remove it you have to remove all the hydraulic lines. If you remove the the hydraulic line you have to bleed the system later which only dealerships can do because it requires special software, which means an expensive tow and labor bill from BMW even if you're lucky to fix the pump yourself.

I have found someone was able to remove the motor from the pump without disconnecting any of the hydraulic lines so I might be able to remote it and disable the motor and work on it alone

PS basically what I think is happening, the pump/motors probably has about 0.4ohm resistance when new (360watts). After X amount of miles the brushes/commutator get dirty and the resistance goes up probably in the 0.8ohm range making the pump not drew enough power (only 180watts). If I could fix this with a higher voltage (~17volts) to the pump why not? Pump would still be using same power (360watts) as when it was new just at different voltage

 

[Gryd3]

PS basically what I think is happening, the pump/motors probably has about 0.4ohm resistance when new (360watts). After X amount of miles the brushes/commutator get dirty and the resistance goes up probably in the 0.8ohm range making the pump not drew enough power (only 180watts). If I could fix this with a higher voltage (~17volts) to the pump why not? Pump would still be using same power (360watts) as when it was new just at different voltage

The thought process is perfectly logical.
If you are dead-set on operating it like this, then the biggest hurdle you have is going to be supplying the required current at the higher voltage.
If you can manage to find a 17V source that can provide 30-40Amps then you could use a 12V relay to intercept and dump the higher voltage into the motor with minimal alterations to the car's wiring.
The Capacitor method would involve a large capacitor bank, a method to charge it and a more careful addition to the wiring to ensure you don't accidentally feed the capacitor back into the vehicle, as it sounds like you would want the 14.4V from the alternator to continue to provide current once the capacitor empties.

The hope I had with a wrecker was based on my experiences with the local wreckers. We have one called 'pick-a-part' which is a self-serv wrecking yard. Show up with a couple tools and pull your own part from a wrecked car in the yard. Costs are pretty slim for the parts, and if you only grab the DC motor and not the assembly or pump the cost should remain low.
DC motor repairs are common, which is the path I would like to encourage you to go. Getting your hands on a broken or budget DC motor will let you carry out repairs or experiments with higher voltages without risking the vehicle. I'm not suggesting you simply shell out a couple grand for a 'working' model considering it sounds like you are the type that wants to carry out a repair yourself.

 

[BobK]

I don't see a mechanism for a motor to lose torque without failing completely, so what is probably happening is the mechanical load has increased due to wear on the pump. Is it possible to replace the pump without replacing the motor?

Bob

 

[supak111]

Yes some company in UK finally makes the motor* and it can be replaced by itself but its $600+sh...

Issue is that you will not find this pump at the junk yard, this is a BMW M-3, they don't end up in junkyards much and when they do most junk yard sell these high end parts online for a premium.

and a more careful addition to the wiring to ensure you don't accidentally feed the capacitor back into the vehicle, as it sounds like you would want the 14.4V from the alternator to continue to provide current once the capacitor empties.

YUP, 14.4V needs to continue flowing after the CAPs have discharged, and I def don't want the CAP to discharge back into the car's battery. I think a 50amp diode might be ok here?

Why would I need a big capacitor bank? I think even getting ~17V to the motor even for a 1/10 of a second might do the job but I'm planing on adding 8 - 2.7v50f ultra caps, thats a lot of power (~900 joules).

Maybe my logic is wrong but that how I see it work.

And I will try to fix the motor first don't get me wrong, issue there although you can take the motor off the pump I haven't found one person that was able to open the motor and repair it so Im thinking the motor isn't easy to take apart.

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[supak111]

One thing I forgot to mention, the relay that control this pump constantly fails. People usually replace it every 15-20k, pump is very hard on the electrical. Not sure if bmw engineered it wrong or its just how it has to be just though I'd mention that.

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[Gryd3]

Why would I need a big capacitor bank? I think even getting ~17V to the motor even for a 1/10 of a second might do the job but I'm planing on adding 8 - 2.7v50f ultra caps, thats a lot of power (~900 joules).

Connecting 8x 50F Capacitors in series will provide you with an equivalent capacitor of 6.25F rated for ~22V.
My math is a little rusty, but if that motor draws 30Amps at 14.4V, then we can estimate a 0.5Ω resistance.
Discharging the equiv. capacitor from 17V to 14.4V will take approx. 1/2 second and will provide at most 34A to the motor.

If you can find a capable double pole, double throw relay, you can easily make/break a parallel/series connection of a capacitor. The part that concerns me however is the relay failing and inadvertently grounding a power line, or grounding the output of the relay.

As far as the higher voltage source is concerned, you can find some very inexpensive 'boost' type switch mode converters that can bump your 12-14V source up to 17-20V quite easily. Current output will be an issue, but if you use a suitable resistor to limit the charge current you should be fine.

I don't like it, but it's your choice. I'd be trying my damnest to get my hands on the broken motor/assembly to see if I could repair it instead of jurry rigging something like this. I sure hope you either never sell/donate the vehicle with this mod in place.

 

[Minder]

I'd be trying my damnest to get my hands on the broken motor/assembly to see if I could repair it instead of jurry rigging something like this. I sure hope you either never sell/donate the vehicle with this mod in place.

Likewise, If it were me I would be curious to find out exactly what the area of the problem source is, is it due to electrical or mechanical causes?.
IOW do an autopsy on an old unit.
Rather than coming up with some jury rigged solution that may be just a temporary patch.
M.

 

[Alec_t]

Thanks for the heads up. I won't be buying a BMW any time soon .

 

[73's de Edd]

.

Sires . . . . . . .


Oy Ye . . . . .Oy Ye

all Beamers afficianados . . . . .

I guess thats jes' the price . . . whut you done gots to pays . . . . . for high performance hy-dree-awl-licks shifting . . . . . .

Pristine unit . . . . .

Replacement . . . .2 screw mount . . . . motor
( Its case / housing footprint, looks akin to what you might have have seen on a 1/3 longer blower / air ventilation motor of a 58 Cadillac. . . . . . less the modern implementation of exotic, ultra high strength field / polar magnets.)

Pulled unit . . . . .

Modus emplus . . . . .

Typical 17 hour R&R task . . . hee . . . hee . . . .
(Wonder where the homeowners org representative is ?)

73's de Edd

 

[Rapidrob]

You may want to try a "Soft Start" device. There are many ways to do this. This will help protect burning out or welding the brushes in the motor or shorting out the rotor due to the heat breaking down the wire coating.
I have used these devices on several projects and they increased the life of the equipment by at least 40% or more.
Here is a little info on the devices. Many to choose from.
http://electronicdesign.com/power/simple-soft-start-circuitry-provides-long-startup-times.
Another factor that may be causing a problem is hydraulic-lock. Your cars engine is at rest,so is the fluid. A sudden start up on a cold day has the fluid sluggish to move and may even be cavitating the pistons or impeller causing damage over time.
There may be an unloader or relief valve as an aftermarket device to aid in start up. If these pumps are so expensive you can be someone has found a way to stop the failures.