Rebuild BM2 green...

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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 19:39

Where would I find the MOSFET type? on the top side of it?

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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 19:43

Burgerman wrote:
Burgerman wrote:
Trans MOSFET N-CH 55V 85A 3-Pin(3+Tab) TO-220AB

Does it help?

Where is the sense resistor?


No, thats what it said on the 50A photo one!


Must have missed that, I'll go look again. However the device you linked to is still manufactured (just no longer stocked by my usual supplier) but its a recent (11/2014) product, unlikely to be found in a >5y old controller..
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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 19:46

steves1977uk wrote:Where would I find the MOSFET type? on the top side of it?

Steve

Yes on the side opposite the tab.


Incidentally these devices are limited to 75A by the TO220AB package. The silicon is good to 175A. So with only 2 parallel devices 150A is the maximum you can upgrade it to.
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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 19:54

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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 20:17

OK I give up, I've looked again and can't see it..

As far as current sensing, I'd hazard a guess the two devices in the middle on the lower row are either resistive shunts or hall-effect sensors

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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 21:07

No. Those just go to the relay. And that would do what the roboteq does and sense battery current?
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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 21:16

Burgerman wrote:No. Those just go to the relay. And that would do what the roboteq does and sense battery current?

yes, I can see that now. Might not be sense resistors but just some carefully sized PCB tracks..

still can't see where that info was written, must get new glasses :lol:
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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 21:18

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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 21:28



Are those the actual devices?

OK, slightly better than I expected 11millohm at junction temp of 20degC, so about 17milliohm at working temp. Still nowhere near the best available
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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 21:44

It's just a general specshet on the IRF1010N. If these were replaced, what would be a better replacement?

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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 23:43

http://www.eurotech.co.uk/dynamic/detai ... +RECTIFIER

Would safely allow more power. But the controller somehow senses output current. So power would be limited to 50A regardless. So you would need to swap ALL the power mosfets, and find the two current sensors and fool them.
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Re: Rebuild BM2 green...

Postby Irving » 05 Feb 2016, 12:26

The ones BM linked to, or a host of others. The key parameter after on resistance, drain-source voltage and continuous drain current, is input capacitance. If its massively bigger the driving circuit might not be able to turn the MOSFET on fully/fast enough which would be self-defeating. If I was going to upgrade my controller I'd want to put a scope on it on the bench first to see the pulse timing before choosing a replacement device.

Its possible there is no current limit sensing, just temperature sensing for rollback, in which case replacing the MOSFETs with ones that run cooler will increase the output capability anyway.
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Re: Rebuild BM2 green...

Postby Burgerman » 05 Feb 2016, 13:22

When you set "turn rate" to 20% at max stick, by way of an e.g; thats what you get. A 20% pulsewidth to zero turn - provided motor compensation is off or set to zero. OR if theres no physical loading..
That means a motor with a stall current of 100A will only pull 20A from the battery, so the chair will not zero turn.

What you actually get, if you turn motor compensation up to the correct value, is 100A even with a 20% input command (if needed), to initiate this zero turn. So *something* is definitely measuring current! Quite what, I have no idea. But there are a lot of small chips on that board that are copied on each side. No doubt one of those is reading mag field or something (hall) somewhere.

Theres another issue with upgrading past 100A though. The daft connectors they use, and the way that the current is sent to the wiring by pushing the tabs against the terminals with a foam rubber strip! That would need at least bolts, and better soldered wiring.
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Re: Rebuild BM2 green...

Postby Irving » 07 Feb 2016, 14:21

The current sense would generally be either between ground and the source leads of the MOSFETs making up the lower half of the H-bridge or in the output lead to the motor. Either way its in a high current area so unlikely to be a small component.


Burgerman wrote:... So *something* is definitely measuring current! Quite what, I have no idea. But there are a lot of small chips on that board that are copied on each side. No doubt one of those is reading mag field or something (hall) somewhere...
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Re: Rebuild BM2 green...

Postby LROBBINS » 07 Feb 2016, 16:44

A shunt can also be a piece of wire with just enough resistance to give a measurable voltage drop - the charger I'm using does its current sensing that way. Ciao, Lenny
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Re: Rebuild BM2 green...

Postby Irving » 08 Feb 2016, 13:44

LROBBINS wrote:A shunt can also be a piece of wire with just enough resistance to give a measurable voltage drop - the charger I'm using does its current sensing that way. Ciao, Lenny

That's why I suggested it might be the PCB track between the source pins of the lower MOSFETs and the ground bus/plane. Its easy to control the 'resistance' of that and you only need one or two tenths of a volt, so we're looking at 2milliohm.

Incidentally, while perusing MOSFETs for my controller, I found some that have a built-in current sense connection; e.g. NXP's BUK7909-75AIE (75v, 75A, 8mOhm) gives a current out that's 1/500 of the drain current, so a 10ohm resistor to ground gives a 1.5v signal at 75A which makes it easy to sample with an ADC input on a microcontroller with no additional circuitry.
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Re: Rebuild BM2 green...

Postby Burgerman » 10 Feb 2016, 17:56

Battery fits... Thats a work of art!

Now sort wiiring, lights, and the fan controlled by the recently installed thermostat, and make a footrest...
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Re: Rebuild BM2 green...

Postby rustyjames » 10 Feb 2016, 20:47

Wow, that is a work of art, and coming along nicely.
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Re: Rebuild BM2 green...

Postby hank » 10 Feb 2016, 21:47

8-) 8-) Pimp my Ride.
Will look well with that new seat back fitted. :mrgreen:
f55s bm1 clone.
quickie groove Brushless
BM3 clone
Foldawheel PW 1000 XL.
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Re: Rebuild BM2 green...

Postby Burgerman » 10 Feb 2016, 22:03

And go well. As long as the seat back isnt narrower than my body...

This should have an enormous range. Will will hind out in about 10 days.
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