Thanks Fetcher, as usual great knowledge here !fechter wrote:Yes, 30A going through those tiny things. And you can bet they get hot. They have pretty high temp ratings, but eventually you can melt the solder off (bad). Most BMS boards use the same little resistors now. I haven't seen anybody melt them off yet.
If the PC board has heavy copper and good thermal connection to those resistors, the heat gets spread out over a much larger area and they seem to do fine. Stacking them might not be ideal. Much better if they are all stuck to the board, but there's not much room. If you remove the two and scrape the solder mask off to the sides, you might be able to squeeze in 3 in a row.
Eh eh clever ! So with two 3mOhm in parallel, you get 1.5 mOhm instead of 2.5 mOhm... Exactly 50Amps instead of 30 amps (or 45A with 3 x 5 mOhms).. I'm a bit concerned about power ratings though .... Each resistors would have P = 0.003 x (25)^2 = 1.875 Watts.... I'd check the 3 mOhms resitor power rating just to be sure... if they are 1.5W, pushing 1.9W might overheating them, possibly making their resistance value drift ? Unless there rated for more than 1.5W ?fechter wrote: I bought some 3mohm ones the same size I can replace them with .
I kinda get it.... So there's maybe like 50-75 mV @30A OEM (or in this order of magnitude ) that go to the LM318. Tapping that little resistor going to it would'nt be a problem, as the voltage and current going throught it is so small, that even a long wire going to the handlebar will not significantly affect it (should be okay with 14awg)...fechter wrote:In the closeup pic of the shunt resistors, you can see the 8-pin LM358. Voltage from the shunt goes to that and gets amplified to a level the MCU can use. Someplace I reverse engineered that part of the circuit. It's pretty simple. If you wanted a remote switch to lower the current, you could tap into the little resistors going to it. It's easy to lower the limit in software too.
The 3077s are good. Way better than the 75NF75s. These will generate much less heat than the old ones. There may be some better ones out there, but too expensive for me. These seem to be the most economical.
Concerning the rating of the resistor, I made some measurments on the picture (using documented size of LM358 and the rule of three). The OEM resistor really look like they have the "2010" size factor (5.0 x 2.5 mm ; 0.20" x 0.10") (Please correct me if I'm wrong). With that size, I'm pretty shure each 5 mOhm resistor has a 1.5W max rating (from datasheet : http://www.ttelectronicsresistors.com/d ... s/LRMA.pdf) I also measured the size available on PCB : The 2512 packet form (6.35 x 3.2 mm ; 0.25" x 0.12") of equivalent resistance value should be rated for 2 or even 3W !fechter wrote:The shunt resistors would be over the rating, but unless you keep the motor at max current for like 5 minutes straight, they probably won't overheat. I haven't tried this on a BBSHD yet, but lots of experience with the ones on BMS boards which are running the same kind of current. Also the watt rating of those resistors is highly dependent on how much heat sink they have. With enough cooling they can probably do 10W. On another project I put Kapton tape over the resistors as an insulator, then used silicone glue to attach a piece of aluminum over the tops. Probably overkill here, but something to consider if one actually melts off.
When I get back to work, I think I have some of the current amplifier information. I remember its a dual amp but only one side is used. The circuit also has an offset so the MCU sees over a volt at zero current. You could tweak one of the two resistors in the amplifier circuit to change the gain.
Yeah I figured I should'nt have much hope either. I'm already in the process of ordering 1 or 2 new BBSHD controller. Will probably get a quote on monday if the seller stocks them.fechter wrote:I wouldn't have much hope of fixing it, but you never know.
I practiced on a dead one first myself. Removing the FETs without damaging anything is not easy. The gate traces don't have much copper on them and pull off pretty easy. The source and drain have big copper so you need more heat. I used a solder sucker and eventually got them all.
Actually, I didn't try them. Although I do have two more original resistor I could unsolder and use from a dead BBSHD controller I bought on eBay.... The thing is , i didn't buy a spare controller to mod yet. and still working on my batteries to be able to actually deliver 30A reliably over the course of a full discharge cycle, without getting to warm.... You'll see... nut many commercial pack are designed for medium to high amps... unless you're willing to carry a heavy battery !Epyon wrote:Hey guys, new here, and very interested in performing this mod.
@fechter Have you made any progress with the current amplifier?
@Matador Any links to recommended shunt resistors other than the 5 mΩ ± 1% 1.5W on DIgikey? Or do those work just fine?
I have the BBSHD controller opened in fron of me (label : CR R10E.1000.SN 852-7-501 1603310055 48V30A).sather wrote:I tried using the BBSHD with a 61 volt battery. It refused to come on until I dropped it to 60 volts. Then it worked fine. Also, the BBSHDs capacitors are rated 60 volts.
Thank you. Just ordered a few.fechter wrote:Tweaking the little resistors in the current sensing amp circuit will be tough simply because the parts are so small and hard to access. I think it is much easier and more foolproof to simply replace the shunt resistors.
From my measurements, the case size seems to be 2512.
3 milliohm (would give you 50A if you replace both)
http://www.mouser.com/ProductDetail/Vis ... xy7w%3d%3d
If you just replace one of the pair with 3mOhm, you would get 40A.
Another approach would be to leave the stock shunt resistors and place another one stacked on top. Less work, but I'm not sure about the heat dissipation.
If you stacked another 5mOhm on top, it would give you 45A.
You can always turn down the max current in the programming.
Stock limit is 30A, so 50A is not quite double. Actual should be about 5/3 x programmed setting. To get 30A, program limit to 18A.Epyon wrote: Thank you. Just ordered a few.
Now, if I replace both, I'd set current limit in programming to half of actual?
I'm curious.... Did you try running a voltage higher than 60 volts to the controller ?Epyon wrote:A big thanks to you guys. I swapped out my shunt resistors and capacitors.
The HVC is at 61.5v I believe. I haven't played with it much to see exactly. Any help on bypassing the HVC would be awesome. Still waiting on a bare controller housing from Luna before I can put it on the bike.Matador wrote:I'm curious.... Did you try running a voltage higher than 60 volts to the controller ?Epyon wrote:A big thanks to you guys. I swapped out my shunt resistors and capacitors.
What shunt values did you use ?
Nice. At 61.5V HVC, you could use a 15S Li-Ion battery, charging to 4.10V max. At 63V, you could charge that 15S to 4.20V. But the HVC won't allow the controller to work.Epyon wrote:The HVC is at 61.5v I believe. I haven't played with it much to see exactly. Any help on bypassing the HVC would be awesome. Still waiting on a bare controller housing from Luna before I can put it on the bike.Matador wrote:I'm curious.... Did you try running a voltage higher than 60 volts to the controller ?Epyon wrote:A big thanks to you guys. I swapped out my shunt resistors and capacitors.
What shunt values did you use ?
I used the resistors from Mouser that Fechter linked above.
I originally had 15s LiPo running, but killed a few cells in testing (cheap Zippys).Matador wrote: Nice. At 61.5V HVC, you could use a 15S Li-Ion battery, charging to 4.10V max. At 63V, you could charge that 15S to 4.20V. But the HVC won't allow the controller to work.
I'm curious, why did you change the capacitors to higher if the bottleneck is the 61.5V HVC ? Is there a way to change the HVC value ??? I't be more interested to up the controller voltage than the amps it can take !
I have an empty controller case. Is there a place where we can buy the controller without the metal case (for cheaper than the whole thing) ??? If so, I'd buy a few and start up experimenting !