MSX 84V mosfet blown. Options?

[US69]

50 minutes ago, Marty Backe said:

I've never understood the exact sequence that causes this to happen to some people. I've never experienced anything but the smallest of sparks.

Never say never...i have even seen that sparks when people UNplug their batterycables.

It shouldnt...but when the batterypacks have different resistance and/or voltage, and dont run exactly same...or the capacitor is empty...it just might happen. 

And seeing what energy sits behind these packs, i always get frightened seeing „bad build“ custom packs and people fiddling arounf with the batterys.....

[Marty Backe]

16 minutes ago, US69 said:

Never say never...i have even seen that sparks when people UNplug their batterycables.

It shouldnt...but when the batterypacks have different resistance and/or voltage, and dont run exactly same...or the capacitor is empty...it just might happen. 

And seeing what energy sits behind these packs, i always get frightened seeing „bad build“ custom packs and people fiddling arounf with the batterys.....

But this is the connector that goes to the control board so it can't have anything to do with battery packs at different voltages. And the capacitors are always empty on my wheels because I discharge the capacitors before working on the wheel.

I guess I'll just have to wait for it to happen to me 

[Arbolest]

1 hour ago, Marty Backe said:

I've never understood the exact sequence that causes this to happen to some people. I've never experienced anything but the smallest of sparks.

In this case I think it probably has to do with him having just changed a MOSFET. If I understand the board circuitry correctly, the MOSFET is tapped directly into (and controls) the battery pack voltage going to the motor and is simply signaled/controlled by the rest of the control logic. If that's the case, then if it was damaged internally in a specific way it might have caused a direct short back to the battery through the motor, which means when he connected the last terminal of the power connector (XT150s come in 2 parts I believe...) it closed a short circuit, and these huge batteries of ours can be friggin' MEAN when there is a good short...

[US69]

Just now, Marty Backe said:

But this is the connector that goes to the control board so it can't have anything to do with battery packs at different voltages. And the capacitors are always empty on my wheels because I discharge the capacitors before working on the wheel.

I guess I'll just have to wait for it to happen to me 

I totally understand you....to me it also never happen...but i really have even seen that Unpluging sparks on video, so i just dont get it!

So press thumbs we stay on the lucky side :-) 

[Hansolo]

7 hours ago, Marty Backe said:

I've never understood the exact sequence that causes this to happen to some people. I've never experienced anything but the smallest of sparks.

The mosfet was in short circuit after replacing them...

Certainly that it wasn't that out-of-service mosfet when they burned

[Hansolo]

On my MSX, I put an XT90 connector anti spark, it's magic no spark

[Marty Backe]

3 minutes ago, Hansolo said:

The mosfet was in short circuit after replacing them...

Certainly that it wasn't that out-of-service mosfet when they burned

OK, now I understand 

[mrelwood]

The key to avoid sparks is not to join batteries with larger than a 0.1V difference. For connecting batteries to the mainboard, the connection must be done fast, not gently or wiggling the connector.

I always measure the mosfets after replacing them, since it will reveal if the mosfet driving circuits have critical issues.

The only time I got a spark from a XT60 connector was when I was about to measure the battery voltage at the free connector.

My meter was set to measure current.

I got the stains off pretty well, but the probe is forever a bit shorter.

Considering how triple-check careful I always am when working with batteries, I’m still ashamed about that year old incident.

[evil696]

Did you repair your V3?

Sparks are caused by charging capacitors, or if wheel have 2 battery packs differences in voltage, there is no other option that makes sparks on working wheel.

I seen this motherboard only on pictures from internet can you take some photos.

There is chance that you have mosfet driver burned and or MCU, if that happend Laboratory PSU will be helpfull.

22 minutes ago, mrelwood said:

My meter was set to measure current. 

My colleague do the same thing and one probe from multimeter just gone.

[esaj]

On 7/17/2019 at 6:34 PM, Marty Backe said:

Really? This doesn't really make sense. It's not like you are buying carpet, fabric, tiles, etc. where you want the colors to match.

Components are manufactured and tested to a specification. If your components match your application requirements than you're good.

It may make sense in special-cases, like things that are built-to-order (and usually cost some serious $$$, like >1GHz scopes, only directly from manufacturer, prices are 5- or 6-digits), people building analog audio circuits like pedals and analog synthesizers (like a friend of mine who "lives" in our garage during the summer, building cases for them ) often have to go that route (matching components and whatnot). Never really dug deep into there, as I haven't been bitten by the bug (yet ). 

On 7/18/2019 at 1:15 PM, mrelwood said:

I don’t doubt the argument that Mosfets best to be from the same lot. Regular resistors for example have a tolerance of +-10% or even +-20% (carbon resistor). When building guitar effects using J201 fets, one has to buy a bunch and screen them oneself due to huge tolerances. I have no idea what the power mosfet tolerances are, but no reason to doubt that they can be notable as well. 

As for resistor tolerances, 1% basic resistors cost about 1cent/piece these days when bought in lots of 100 pieces or more, so I haven't seen the need to use 5% or more tolerances, the savings are nothing.  J-Fets might be different, and like said above, analog audio circuits are a special case really.

For mass-produced consumer products, I doubt the manufacturers would go the way of matching components, but likely mosfets bought at the same time are from the same batch. In general, many EE's seem to frown at paralleling mosfets instead of using higher rated single mosfet, it's considered bad practice, but it can often be cheaper to use two cheaper mosfets in parallel than one better rated one, which likely is the reason the wheel's use parallel configurations instead of "proper" single device.

At least Toshiba, IRF/Infineon and Nexperia have published longish application notes on problems and issues with paralleling power mosfets specifically, and at least Infineon and Nexperia suggest that optimally the mosfets should come from the same batch if parallel configurations are used, but mostly it's just a matter of handling the gate drive "correctly" to avoid parasitic oscillations.

https://assets.nexperia.com/documents/application-note/AN11599.pdf

https://www.infineon.com/dgdl/para.pdf?fileId=5546d462533600a401535744b4583f79

http://www.irf.com/technical-info/appnotes/an-941.pdf

https://toshiba.semicon-storage.com/info/docget.jsp?did=59458

 

In the past, I've done exactly one device which used paralleled mosfets (5 in parallel), but it could put out >1000A in short spikes (1-10 milliseconds, spot welder), and I followed the application notes on the basic suggestions how to ensure the turn-on and -off don't cause problems and the load is shared as equally as possible (gate resistor with anti-parallel diode to speed up the turn-off, ferrite beads to increase high frequency impedance and kill off parasitic oscillations). All the mosfets were ordered at the same time, so likely the same batch. For anything "critical", I wouldn't order the parts from Aliexpress or such, you can never know whether you get some other mosfets with changed "stamping" on the package, clones, used devices removed from a broken device, factory rejects (don't fulfill the datasheet specs) or the genuine thing.

 

19 hours ago, Marty Backe said:

I've never understood the exact sequence that causes this to happen to some people. I've never experienced anything but the smallest of sparks.

 

17 hours ago, Marty Backe said:

But this is the connector that goes to the control board so it can't have anything to do with battery packs at different voltages. And the capacitors are always empty on my wheels because I discharge the capacitors before working on the wheel.

I guess I'll just have to wait for it to happen to me 

If the capacitors are discharged, you may or may not get sparks, it's all down to how good a connection you do (and how fast). The initial current when the capacitors sit at (or near) 0V, and a battery pack with 60...80...100V or whatever is connected, can be huge. If the connectors are touching "badly" (only slightly), the highest resistance point is at that connection, yet the resistance may still be low enough to allow substantial current (like 100...1000+A in a very, very short spike). Most of the voltage gets dropped over the highest resistance in the circuit, meaning most of the power is dissipated there, and the short-lived but very high power dissipations there (think 10kW or such, the above 1000+A spot welder used 12V and could go above 10kW peak when the "short circuit" starts) is enough to melt small amounts of metal (that's the sparks you see, tiny molten bits of copper or whatever the connector's made of). The battery BMS's have (or at least should have) short-circuit protections, but they still take few milliseconds to react, which is too slow to prevent this. The "anti-spark" XT90's have a clever internal structure where the connection is first made over a resistor that limits the current, but is low enough to allow the capacitors to charge before the final very low resistance connection is made, and at no point the current spikes into really high numbers.

9 hours ago, mrelwood said:

The key to avoid sparks is not to join batteries with larger than a 0.1V difference. For connecting batteries to the mainboard, the connection must be done fast, not gently or wiggling the connector.

I always measure the mosfets after replacing them, since it will reveal if the mosfet driving circuits have critical issues.

The only time I got a spark from a XT60 connector was when I was about to measure the battery voltage at the free connector.

My meter was set to measure current.

I got the stains off pretty well, but the probe is forever a bit shorter.

Considering how triple-check careful I always am when working with batteries, I’m still ashamed about that year old incident.

Been there, done that...  Luckily no other damage than a destroyed probe and XT60-connector.

Edited July 19, 2019 by esaj

[mrelwood]

13 hours ago, evil696 said:

Did you repair your V3?

If you are asking me, it’s the MSX, and I have a new board on the way. Should be here next week.

13 hours ago, evil696 said:

Sparks are caused by charging capacitors, or if wheel have 2 battery packs differences in voltage, there is no other option that makes sparks on working wheel.

I am especially prudent in reaching the same voltage if I connect two packs of batteries. I only connect and recharge the wheel with one pack if the pack is lower in voltage.

13 hours ago, evil696 said:

I seen this motherboard only on pictures from internet can you take some photos.

Will do.

13 hours ago, evil696 said:

There is chance that you have mosfet driver burned and or MCU, if that happend Laboratory PSU will be helpfull.

Unfortunately I don’t have a PSU that I could borrow.

 

[esaj]

2 hours ago, mrelwood said:

Unfortunately I don’t have a PSU that I could borrow.

If you need a reliable low voltage lab PSU in the future (for guitar pedals or whatever), look no further than HP6632 (A or B), which are relatively easy to find as second-hand, this is a serious industrial-grade 100W programmable linear lab rack PSU from the 80's/90's (production discontinued in 2017) with proven track record. East Trade Promotion sells such for example (not sure if they have any in stock right now, but there have been plenty in the past), I bought mine from them through huuto.net:

http://sivut.klikkaa.fi/eastrp.fi/webshop/product_details.php?p=45

https://www.keysight.com/en/pd-838596-pn-6632B/100-watt-system-power-supply-20v-5a?&cc=FI&lc=fin  (The reason the specs are  in Keysight-website is that HP instrument-division first became part of Agilent and then Keysight)

Output Ratings

• Output voltage: 0 to 20 V
• Output current: 0 to 5 A

Programming Accuracy at 25°C ± 5°C

• Voltage: 10 mV
• + Current: 0.05% + 2 mA

Ripple & Noise (20 Hz to 20 MHz)

• Voltage Normal Mode rms: 0.3 mV
• Voltage Normal Mode peak-to-peak: 3 mV
• Fast mode rms/ peak-to-peak: 1 mV/ 10 mV
• Current rms: 2 m

https://www.eevblog.com/forum/reviews/hp-6632a-20v-5amps-programmable-psu/

"They are super precise , and can sink & source current.
The meters are/were the most accurate i had when i bought them."

Mine was off by about 4mV (0.004V) higher up in the voltage, that's about it. Hasn't been calibrated in 10+ years.

In a pinch, it'll work also as a load up to 20V/5A, although at least on mine the down-programmer has an issue where the sinked current will be about 250mA higher than what's programmed, guess it's an general issue (it's not like it was meant to be used as such ): https://www.eevblog.com/forum/testgear/hp-6632-current-sinking-performance/

Not that big of an investment money-wise (I think I paid 120€ for mine with rack-ears, including shipping), the size might be an issue (2U rack-unit), plus it weighs 10+kg.

Edited July 19, 2019 by esaj

[Rehab1]

18 hours ago, mrelwood said:

The key to avoid sparks is not to join batteries with larger than a 0.1V difference. For connecting batteries to the mainboard, the connection must be done fast, not gently or wiggling the connector.

I learned that lesson the hard way a few year’s back.

 

Edited July 20, 2019 by Rehab1

[Rehab1]

21 hours ago, Hansolo said:

On my MSX, I put an XT90 connector anti spark, it's magic no spark

I did the same thing on my old ACM. 

[mrelwood]

New board arrived. Powered on, 2 seconds of relief and bliss, and the wheel kicked and started a violent rodeo while beeping an error code. So I started disassembling the motor itself, which revealed that the motor cables were melted and shorting inside the axle as well.

I will next replace the motor leads all the way from the coils. I was going to go with PTFE cable, but the local availability is not as good as I had hoped.

Local regular cable is rated up to 150•C, while PTFE would be 200•C. Am I being overly conservative with the PTFE, or would a regular suffice, since regular solder melts already at around 180-190•C?

[Marty Backe]

12 minutes ago, mrelwood said:

New board arrived. Powered on, 2 seconds of relief and bliss, and the wheel kicked and started a violent rodeo while beeping an error code. So I started disassembling the motor itself, which revealed that the motor cables were melted and shorting inside the axle as well.

I will next replace the motor leads all the way from the coils. I was going to go with PTFE cable, but the local availability is not as good as I had hoped.

Local regular cable is rated up to 150•C, while PTFE would be 200•C. Am I being overly conservative with the PTFE, or would a regular suffice, since regular solder melts already at around 180-190•C?

Wow, you really did a job on that wheel 

Did you carefully inspect the hall sensor wires. Hopefully none of the insulation on those wires melted.

[Michael Tucker]

On 7/19/2019 at 6:53 PM, Rehab1 said:

I learned that lesson the hard way a few year’s back.

 

Wow! Is that paint, or did it burn your hand?

[evil696]

Bad luck, but when you get new motherboard you dont do anything else that replace. So there is no other option that something else is burned.

If wheel starts to do something like this i think that could be hall sensors broken it could happend when Mosfet burns->Mosfet driver -> MCU-> hall sensor.

if you change wires first check resistance on hall sensors.

[evil696]

Today or tommorow i will replace hall sensors in V5F, there is 3 hall sensors SS41F i will try to replace all of them.

[mrelwood]

3 hours ago, Marty Backe said:

Wow, you really did a job on that wheel 

Did you carefully inspect the hall sensor wires. Hopefully none of the insulation on those wires melted.

One of the hall sensor wires has damage to the insulation in two spots, so I will be replacing at least one of those as well.

Regarding the main motor wires, I learned after my last post that the originals must have been PTFE as well. So regular was out of question. I bought silicone shielded wire that’s rated to 260•C, and glass fiber shielding to improve the durability of the silicone shielding.

Will replace the wires later today. If it still doesn’t work, I’m going to wish I’d drink alcohol.

[Arbolest]

32 minutes ago, mrelwood said:

Will replace the wires later today. If it still doesn’t work, I’m going to wish I’d drink alcohol.

Good luck my friend!  

[evil696]

Before you connect battery just check shotcuts on hall sensors if anything will be shortcuted dont connect battery. If you would live closer i will help you.

[Marty Backe]

7 hours ago, mrelwood said:

One of the hall sensor wires has damage to the insulation in two spots, so I will be replacing at least one of those as well.

Regarding the main motor wires, I learned after my last post that the originals must have been PTFE as well. So regular was out of question. I bought silicone shielded wire that’s rated to 260•C, and glass fiber shielding to improve the durability of the silicone shielding.

Will replace the wires later today. If it still doesn’t work, I’m going to wish I’d drink alcohol.

This is the pinnacle of EUC repair, so hats off to your nonchalant attitude of tackling all the repairs 

Me? I would bought a new motor at this point   

[mrelwood]

 

28 minutes ago, Marty Backe said:

Me? I would bought a new motor at this point   

I know I’m in a minority with my attitude to fix everything and passable repair skills regarding electronics. If there was a shop next door with MSX motors for a few hundred bills, I’d have been hard pressed to buy one as well. But while the 16S is now a decent ride (after the second battery repair), I want the MSX up and running as soon as in any way possible.

I replaced all hall sensor wires, no point in mixing new and old.

[Nils]

1 minute ago, mrelwood said:

I know I’m in a minority with my attitude to fix everything and passable repair skills regarding electronics. If there was a shop next door with MSX motors for a few hundred bills, I’d have been hard pressed to buy one as well. But while the 16S is now a decent ride (after the second battery repair), I want the MSX up and running as soon as in any way possible.

I replaced all hall sensor wires, no point in mixing new and old.

That's the spirit, nice to see some sisu in action!