Much More Powerful Pie Now!!!

[o00scorpion00o]

Thanks 317537, Just sent you a P.M. 

I can adjust it with the software to my requirements.

Hi

Interesting thread about the shunt bypass.

And take the time to program your controller to meet the BMS and motor specs.

You were warned to do this on the first page. .

I tend to be good at seeing the warning signs because I have made almost every mistake in the book 4 times over.

However!

This is interesting.

Is the software in this case going to help your fets survive?  What AMPS was the controller set to, to begin with?  would of it made a difference to peak currents and voltages?  Maybe not hence the need for the shunt to begin with.

Hi 317537, I didn't try the software after the mod because the cable broke. Wires detached from inside. The cable grip is not so good. So I don't know if it would have made a difference. The controller came set for 30 amps continuous 50 max. But obviously 14 max is all I got. The only thing I changed was the voltage which was set for 24 volts! Turning the amps down to 3 made a difference straight away!

The only fet's I will be able to get are  IRFB3207ZPBF and are rated to 170 amps and 75 volts. I don't know if I should replace all or just the blown fet because if I'm turning the amps down, I should not reach the 120 amps again?

[Leslie]

IRFB3207ZPBF.

From the looks it will work fine.

About replacing a single mosfet, one guy here at GM forums replaced one fet with a 50v fet and its still going.  Pretty sure he was using a 36v pack though.

The resistance is a little lower on the IRFB3207ZPBF not sure how this will behave with the other fets.  It might be a good idea to replace all of them, I would.

[o00scorpion00o]

Ok 317537. I will replace them all tomorrow. And remove the link.

Off to bed now though!

[Leslie]

Ok 317537. I will replace them all tomorrow. And remove the link.

Off to bed now though!

Good luck.

I sincerly hope your sort it out.  Possibly the original shunt wasnt soldered properly in place to begin with.


You could cut some short resistor lead wire.  I Just tested some 10 watt resistor lead over an amp meter and it was good for 15 amps.  I think 5 watt resistor lead is good for 10 amps.  This all depends on the whether the shunt is solid with its soldering..

If you buy a few 5 watt resistors maybe cut and add 2 or 3 of the leads in the place of the GM shunt, from the pics it doesnt look rated.

[Leslie]

Here is another fet that could work.

IRFP2907

http://www.irf.com/product-info/datasheets/data/irfp2907.pdf





You can get 10 here for $39.


http://cgi.ebay.com.au/10-pcs-IRFP2907-IRFP-2907-IR-Power-MOSFET-N-Channel-/370401488583?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item563da62ec7

Not cheap. But looking at the datasheet they seem to perform better under hot conditions than the IRFB3207ZPBF.

The amps are limted by the package at around 90 amps but its silicon limit is 204 amps.


Its R_DS(on) is 4.7mO

Its turn on delay is low at 23ns this to me gives a good reason why we should forgive its rise time at 190ns and off and fall time at 130ns under a lab load of 204 amps.  How it would perform under a lighter load with a good hair trigger is obvious with its on resistance of 4.7mO

I did up a comparison of the datasheet with current and temp coefficiency.

And I thought I add the GM STB140NF75 fet in green.



The STB140NF75 comes ahead of the IRFB3207ZPBF.in the Pie current area.

The IRFB3207ZPBF is King of the 90 and 120 amp range,

Where as the IRFP2907 is the all round performer hands down under 90 amps.

I marked in yellow the current capability advantages of the IRFB3207ZPBF over the IRFP2907 and thermal advatages of the IRFB3207ZPBF has over the STB140NF75

I marked in blue the advatages of the  STB140NF75 thermal advatage over the IRFB3207ZPBF.

And I marked in blue-green the thermal advantages advantages of the IRFP2907

Please excuse any inaccuracies towards the STB140NF75 as the temperature scale was hard to blen I just did a few plots and jouined the dots.

One thing that stood out is the STB140NF75 could do 100 amps at 100^oC. and possibly that the internal controller are not too up to modding current shunts to max without some special considerations to the parts used.


The IRFP2907 can give up 50 more amps at 150^oc  Thats still 90 amps at 150^oc compared to 40 amps the IRFB3207ZPBF at the same temperature.  This to me shows that the IRFB3207ZPBF struggles under high temperature conditions and suffers more from thremal runaway..

The IRFP2907 can still run a 30 amp MP at 170^oc where as the IRFB3207ZPBF is lucky to provide 5 amps at this temperature.

The package isnt a T0-220 with bare metal exposed and probably has less chance of picking up thermals in the motor and bringing heat close to the dye.

I could be wrong and the IRFP2907 package does seem less atractive on the graph at higher current draw due to the package limitation, IMHO the IRFP2907 will out perform the IRFB3207ZPBF with the internal controller application with the MP.

Maybe these findings should be something for GM to look into in the future and maybe something we only think about for now.  A fet like this would bring up the price of the controller in the MP wheel $30 or so but may just be worth the additional expense when considering an internal controller.    

[Leslie]

Last thing I will ask is could you provide the forum some pics of the work you do and some text of how you did it.

[o00scorpion00o]

Hi 317537, I ended up ordering the IRFB3207ZPBF. Pity I didn't see your posts until now!

Of course after driving 110 miles to find a few poxy mosfets. They had 0 in stock after I checked their stock on the internet last night. I was not impressed! Anyway they will have them tomorrow and I have already paid for them.

Do you think they will be ok if I try keep as close to the controllers original specs? 30amps continuous 50 max? I think the pie will still have some serious torque at those ratings!

maybe someday I will hook it up to an external controller, Something maybe that has a soft start option, The torque of the pie @60amps start off, maybe more peak?  is so much that it is too hard to take off steady and then trying to keep the front wheel on the road. But once you get going it is really a thrill! 

I really don't think anyone would need a bmc torque or even bmc 3, though the geared motors do seem to give more speed for the same voltage. I would love to compare those 2 motors with the pie fed with the same batteries and controllers!

Anyway I will get some 5w resistors as you suggested and remove the original shunt and see what happens. 

I love experimenting with these things lol. I will take pics too just in case I don't spot a potential fault before I fire it up!

[o00scorpion00o]

317527 how about 3 of these?

http://radionics.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=6926804

[Leslie]

Resistors for some really weird reason are not the same as shunts. Shunts are like reallly tiny in resistance and do not waste the same energy .

Resistors make a long track for energy to get from one end to another where as shunts use the shortest distance between two points and the maximum a piece of metal can take approach.



You need standard resistors leads.  Like the resistor above.  You cant use a diode or anything else.  It has to be a standard resistor lead and you will have the perfect shunt.

Resistor leads just stick to the normal ceramic resistors are perfect shunts as the leads are designed to a very tight spec.  The purity and guage has to be spot on for the resistor to have military spec tolerances.  Suprising that the science behind resistors does all go back to temperature.

The 10 watt ceramic resistor I cut the lead an inch long off the leads and shorted it across my a battery with my AMP meter the resitor lead gave exactly 15 amps not a ma more.  I blew my multimeter up so I couldnt test the other resistors.   

 

[o00scorpion00o]

Resistors for some really weird reason are not the same as shunts. Shunts are like reallly tiny in resistance and do not waste the same energy .

Resistors make a long track for energy to get from one end to another where as shunts use the shortest distance between two points and the maximum a piece of metal can take approach.



You need standard resistors leads.  Like the resistor above.  You cant use a diode or anything else.  It has to be a standard resistor lead and you will have the perfect shunt.

Resistor leads just stick to the normal ceramic resistors are perfect shunts as the leads are designed to a very tight spec.  The purity and guage has to be spot on for the resistor to have military spec tolerances.  Suprising that the science behind resistors does all go back to temperature.

The 10 watt ceramic resistor I cut the lead an inch long off the leads and shorted it across my a battery with my AMP meter the resitor lead gave exactly 15 amps not a ma more.  I blew my multimeter up so I couldnt test the other resistors.   

 

Okay I will give it a shot. Hopefully I will get it all up and running by tomorrow night 

[Leslie]

The reason I blew my multimeter up on that lead was because I wasnt using the proper multimeter leads.  The resistance of the lead shunt was so low there was no drop allowed over the shunts ends.

There is a reason why one should use proper multimeter leads.  They are designed to melt and take the load off the meter. GOod set of probes can take 15 amps easy without melting in about a 5 seconds load test.

There is no reason why you cant test a few resitors leads though.

I think the 1/4 watt resistor gives 2 amps and makes a good fuse as well for a charger.  And I think 1/2 resistor watt gives 3 amps and a 1 watt gives 5 amps.

You can test them on any 12v lead acid battery on a proper meter with no problem.

You then can get it spot on within 2 amps.  Its not like parallel resitors you can just add a 10 amp and a 15 amp in parallel and get 35 amps.



I would go for 30 amp shunt in place of the old one.  You can beef up the tracks from shunt the to the power pole,

Set the MP for 25 amps cont and 30 amps max and I bet you will be happy with these settings.

[o00scorpion00o]

okay all fet's are in place and the shunts. So I think I'm ready to fire her up and hopefully there will not be any smoke!

If it works I will then order a new usb cable to tinker with the current settings.

[o00scorpion00o]

I hooked it all up, put her on the bike, connected battery turned throttle and yepeeeeeeeee, Decided to give her full throttle and axel spun, I didn't tighten the nuts, OK I didn't even put them on, I just wanted to see if it worked before I put it all together!  Yes I'm an idiot!

I wonder will Tom send me a new one?

[Leslie]

I hooked it all up, put her on the bike, connected battery turned throttle and yepeeeeeeeee, Decided to give her full throttle and axel spun, I didn't tighten the nuts, OK I didn't even put them on, I just wanted to see if it worked before I put it all together!  Yes I'm an idiot!

I wonder will Tom send me a new one?

I was hoping to see some good news in here.

At least your doing mods with the right attitude, I like that about you, youre not whining like a little baby.  I don't know GM may send you a new harness if you email them with some datails, it may cost you though.

That close you were...   

 

[Leslie]

I hooked it all up, put her on the bike, connected battery turned throttle and yepeeeeeeeee, Decided to give her full throttle and axel spun, I didn't tighten the nuts, OK I didn't even put them on, I just wanted to see if it worked before I put it all together!  Yes I'm an idiot!

I wonder will Tom send me a new one?

No youre not an idiot.  You just like to tinker man.  We learn nothing without these experiences.  When you know where you went wrong youre learn 10 times more and to come here and openly share this with us makes you all the more worth any time that I or any one here may spend with you.

This thread is going epic with some very good data coming from the text and pics.  The reward at the end will be to have your wheel working the way you want.

Pick yourself up and dust off your coat and  try again.

Ps:

Can you show us some pics as to what has happened to your wires.

Edit:

Disconnect the battery and clean up the wires,  You may have to replce all of them.

Make sure there is no damage to the PCB. where the wires connect.

You can probably go with an external controller as it may be easier to make the changes you want without taking off the hub.

Depending on the damage there are a many options from your stand point.