Rebuild BM2 green...

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Re: Rebuild BM2 green...

Postby Burgerman » 02 Feb 2016, 22:15

And now the thermostat is inside the case and the fan fitted behind the mounting plate under the seat cover.

810_1272.JPG


So the power module can sit over the hole on 2 8mm spacers so the air can escape underneath in all directions.

810_1278.JPG


And the fan will come on any tie the mosfets reach 45C.
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Re: Rebuild BM2 green...

Postby Burgerman » 02 Feb 2016, 22:43

And the top which will not be seen because there is a flat metal seat plate yet to be fitted:

810_1280.JPG
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Re: Rebuild BM2 green...

Postby expresso » 03 Feb 2016, 01:44

Nice i like that idea - i remember reading about soccer with the chairs and people adding fans to there chairs - but didnt look into that dont remember how they added fans to there chairs -
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 02:25

If you program your chair to go. To stop. To turn. When *you* tell it, and you dart about a bit for a few minutes stopping and turning they *all* start shutting down and rolling back the power. And eventually it gets to the point where the chair barely moves.

Mine only does it when I am clearing leaves with a blower for half an hour when darting around and zig zagging. Because I adjusted the temperature in the programming from 55 to 70 centigrade. So it doesn't usually bother me. But now and again in summer it cuts in and pisses me off...

This should help keep it cool. And with the thermostat chip inside the power module, epoxied to an output mosfets, it should be efficient. Its not easy either. Not any wasted space inside that PM! At 45C the fan is on. At 40C it goes off again. So it only wastes power and makes a noise if needed. It is only a small fan too, but its circulation is quite good because of the way its working and the way the PM is spaced off the surface. The cool airflow around it and from behind it is pretty good.
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 02:37

There will be a 3 position lighting switch on there too. OFF/AUTO/ON. So I can leave it on auto normally, and a light sensor will decide. And a movement sensor.

So on auto: if moving + dark light comes on. If it stops moving or gets light, they go off after say 2 or 5 mins.
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 02:46

I presume you haven't looked inside your power module yet then?

Image
Image :lol:

Nothing to be scared of. You just get to see how crappy the build quality is, wit only a rubber foam pad making the pressure for all the connections to the power mosfets. Amazing they don't fail more often. And that they are using just 8 power mosfets. Unlike the Roboteq with 32... No wonder they get hot really is it.
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Re: Rebuild BM2 green...

Postby shirley_hkg » 03 Feb 2016, 05:36

O M G !

WHAT a confidence they have.
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 11:17

Well surprisingly it does appear to work pretty well! I and the rest of us using all of PG Drives systems, inc Rnet should take the thing apart and use a scotch bright cloth or fine glass paper to clean those contact point every year or so though. It will likely prevent failure.
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Re: Rebuild BM2 green...

Postby expresso » 03 Feb 2016, 17:00

The contact points your talking about to clean - are the plugs where you plug in the cables ? or inside the box itself -
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 17:03

Look at the pictures. Inside. They just press together with a bit of foam! That is supposed to be OK for 100A per motor.

Outside too.
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Re: Rebuild BM2 green...

Postby Irving » 03 Feb 2016, 17:49

I don't suppose you know what MOSFETs they are, or have pics of the other side of the board showing them??
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 17:53

The side with the writing is folded on to the board so not visible without bending them up. I did compare an 80 to a 100 years ago and they were the same. So its only a firmware difference.
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Re: Rebuild BM2 green...

Postby LROBBINS » 03 Feb 2016, 20:32

Could be a firmware difference, or a different shunt in the current measuring circuit.
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Re: Rebuild BM2 green...

Postby Burgerman » 03 Feb 2016, 20:38

Its firmware or the programming tools wouldnt have different limits on the Amp settings? Or maybe both... Theres a feeble 50A one too.
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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 00:41

I have a few 50 amp modules, will open one up and compare with some help from my Brother or Carer.

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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 00:51

Do you realise how feeble that is? My model helicopter weighs 8lb and has a 70A controller which isnt enough, and that actually pulls about 85A at max pitch (no current limiting). Just about adequate to get grandma to the dining room...
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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 10:54

Yup, which is why I never use them. Probably be ok for a kids indoor chair but nothing else. Will ComparethePowerModule.com :mrgreen:

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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 10:57

To increase efficiency and allow lighter wiring and smaller motors/controllers most of the serious model helis are using lipo and 10 or 12S now. So are at 40 to 50 volts. As we should be!
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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 16:59

Convert rear light to LED

Red LEDs in the red, white ones in the turn lights... I have ordered some red ones for those too. Because I have no need of turn signals. They will light up red!

So Projector lamps for the front. And this F55 one for the rear (because I like it) but turned to LED. I may not fit it. Depends on the seat... Might use red projector LEDs on the rear instead. Right now its taking 3 watts at 16 volts... So the 3kwh battery would run it for 44 and a half days.
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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 17:10

Burgerman wrote:To increase efficiency and allow lighter wiring and smaller motors/controllers most of the serious model helis are using lipo and 10 or 12S now. So are at 40 to 50 volts. As we should be!


Interesting trade-off there for helis/quads between battery weight and motor/wiring weight, can't be one-approach fits all...

The reason I was asking what MOSFETs they use is to think on whether they could be replaced with a newer type with a lower Rds(on) (on resistance) and then tweak the current limit. I would expect that current limiting uses a sense resistor that could be changed. The firmware will most likely measure voltage across the sense resistor and once over the limit will roll-back to a lower voltage for a period of time. Changing the limit by changing the sense resistor will retain the same normal v rollback ratio without needing a firmware change.
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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 17:10

50 Amp PM insides...

pm1.jpg


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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 17:18

Lift up a power mosfet and see what its numbers are. Irving wants to know!
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Re: Rebuild BM2 green...

Postby steves1977uk » 04 Feb 2016, 18:06

PG 50 Amp PM 7 Photos inside a 50 amp PM.

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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 19:13

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

Does it help?

Where is the sense resistor?
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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 19:17

but none show the MOSFET type. :(

There are 8 MOSFETs in the H-bridge, arranged in 4 pairs. At any one time only 2 of the 4 pairs is on, each MOSFET carrying 1/2 the current, so if limited to 100A each would be carrying 50A. A typical MOSFET from as little as 4y ago will have an on resistance of around 20milliohm, so heat losses = I^2 * R = 50 * 50 * .02 = 50W, WORST CASE at stall per MOSFET, which is fine with a decent heatsink. It'll get hot (case temp ~100degC) but wont die.

Replace that with a current top-of-the-range HexFET. On resistance 6.5mOhm, so for the equivalent heat loss it can handle 100A, or putting it another way a 100A controller could, in theory, be upgraded to 150A with a reduced heat loss of 36W per MOSFET and a case temperature of around 60degC (assuming its just a sense resistor that needs to be changed as well).

And the price? £14 inc p&p

That's a lot cheaper than a RoboTeq! In fact the Roboteq's oft quoted 32 MOSFETs (per channel?) is arguably overkill using current technology.
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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 19:19

Current technology
:D
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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 19:20

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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 19:22

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

Does it help?

Where is the sense resistor?


Not really, could be any one of 100s of devices...

our posts x-ed
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Re: Rebuild BM2 green...

Postby Irving » 04 Feb 2016, 19:28

Burgerman wrote:http://www.eurotech.co.uk/dynamic/detail.php?part1=AUIRF2805&man=INTERNATIONAL+RECTIFIER

What about one of these?


Actually those are pretty good devices, apart from they are no longer manufactured, not dissimilar to the ones I was suggesting. 55v a bit low for my liking on the regen spikes, but if that's what's fitted then just changing the sense resistor would work to 125 or 130A. I'd not take it to 150A
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Re: Rebuild BM2 green...

Postby Burgerman » 04 Feb 2016, 19:32

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!
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