soldering shunt

Beavinator

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Aug 17, 2010
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I have a 40Amp controller from e-bikes.ca. It has 2 shunts on it and i want to add some solder to make the controller do 50Amps but I am unsure if I just do 1 shunt or both and how much solder to add. Any help would be much appreciated!
 
It's kind of a put some solder on and see what it does type of thing because it's really hard to guess how much solder you got on there and it's resistance. Throw in factors like the resistance increasing in solder as temperature increases, combined with other factors such as how much power you use and how you use it, and it's really hard to give exact instructions about things. Start with one ball at one end, test, modify programming to take advantage of the mod if necessary, test again, add more solder/programming if necessary. Or you could just solder in more shunts and basically go through the same process. I'd do some more research in general before soldering anything if I were you just to get a better idea of the why's for the mods, not just the how's.
 
Be aware that if you use the direct plug in Cycle Analyst that modifying your shunt will throw out your amp readings.
 
Agree with above. But of course, what you really want is a bigger controller. See the Lyens for sale threads, and start saving up about $150.

And you could be at the limit of your batteries at 40 amps anyway. What are you using? More amps won't help if the power only heats the battery.
 
I am using 72V20AH LiFePo4. My battery is limited to 50A cont right now by the BMS but Im ordering a 100A cont BMS.
 
even if your have 100 amps bms or shunt the lifepo4 will not give much more if you have ping battery and also depend what controller you have you need to modify a bunch of stuff inside read! read! i still learn after 3 years :D :D but don't worry you will learn a lot here
 
Add about 3mm of solder from the bottom of one side of the shunts up the legs. Make sure the solder is connecting the shunts together at the bottom. That should give you about 10 more amps peak. Test it then you can ad more or take some away depending on what you like.

Make sure your batteries can handle more peak amps. And wires. Might have to upgrade your main line fuse if you run one.

I whipped out a little example for ya... :mrgreen:
 
Yes, conservative like TMaster said, not like AussieJester did :shock:


file.php


:lol:
 
Gregory said:
Yes, conservative like TMaster said, not like AussieJester did :shock:


file.php


:lol:


I love that "shunt".
That's doing it up with gusto and style.
 
I think for now I will just leave it as is and see how it rides. Im not crazy about throwing the cycle analist readings off.
 
Beavinator said:
Mybattery is from EVAssemble. I have no idea if its the same as a ping

Ping cells are foil pouch type, evassemble pack you have i think they are round blue cells ? .. if so you have Headway cells.. they can so 30 amps without too much stress but try not to go over 50 imo. If you go too hard with the shunt mod you will cause the controller to overheat and fry.
 
I hope you have a programmable controller, because all that copper is likely to make the shunt resistance way too low. As is will be a lot of fun for the first few minutes until you blow your controller. I do like the approach though and will use it on a shunt mod I have to do. My difference will be to wrap half of the shunt length with copper and solder it well with the idea that I'll reduce shunt resistance by a bit less than half. Nah, I'll just use another wire of shunt material like I always do. It's best to err on the conservative side. :mrgreen:
 
liveforphysics said:
Gregory said:
Yes, conservative like TMaster said, not like AussieJester did :shock:


file.php


:lol:


I love that "shunt".
That's doing it up with gusto and style.
Tha'ts not a shunt--that's a full 5-way bypass. :lol:
 
Sorry I didn't realize that was AJ's shunt mod pictured. It actually has the makings of a very good method. If done with a fine braid or maybe solder wick and wrap just a portion of the shunt legs, then that method could be a fairly accurate way to modify a shunt. eg If you want half the resistance in order to double your effective current limits, just solder one end and wrap the copper braid tightly and overlapping up to the halfway point of the shunt bridge and solder in place. That would give it extremely low resistance for half of the length, effectively shortening the shunt wire by half. The advantage in the approach is you can avoid over doing it, since it gives you decent accuracy compared to just soldering. Soldering as a shut mod is just a shot in the dark.

John
 
amberwolf said:
Tha'ts not a shunt--that's a full 5-way bypass. :lol:

NO NO, Its a shunt alright, it just that he didn't have 1000A worth of MOSFETS to go with it :lol:
 
I've just opened up my 14a 6fet mini-controller (this one) to see if I can solder the shunt to increase amps, but I couldn't find anything which looks like a shunt!

Please could someone have a look at the pics and let me know if I've missed it?

Thank you!

Jonathan
https://drive.google.com/file/d/0B...B7ym9WvyF_P7X0RoZ2thWHFoZWs/view?usp=sharing
 
Definitely the 5mOhm SMD (R005) resistor. It probably connects to battery negative.

But given there are wires attached to Rx and Tx can you reprogram the controller through software?

Otherwise you can buy an R004 current sense resistor to replace the old one for 20% more amps for a couple of dollars (or put another in parallel which may be easier to solder).
 
Gregory said:
Definitely the 5mOhm SMD (R005) resistor. It probably connects to battery negative.

But given there are wires attached to Rx and Tx can you reprogram the controller through software?

Otherwise you can buy an R004 current sense resistor to replace the old one for 20% more amps for a couple of dollars (or put another in parallel which may be easier to solder).

Thanks Gregory and Amberwolf. Unfortunately I don't have the software skill or hardware to reprogram, though that's interesting to know. I think putting another in parallel would be easier - would that be soldered on top, pasted on with solder to the existing resistor? Would another R005 double the amperage, and would that new total (30 amps at 36v) be a bit much for a bafang CST 250w 180mm? Alternatively could you recommend another resistor to solder in parallel, which would raise the amperage, but only by 50% or so?
 
Yes, it's a solid stare shunt. The only question is whether there's more than one stacked. You need to look at it edgeways on to see if there's one sitting on top of the other, but .005 is a common value, so it's probably on its own. You can solder another one over the top of it to change its value. First, you have to decide how much extra power you want. To get a 20% increase, you need to change its value to .004. You could unsolder it and replace it with a .004 one or solder a .020 over the top of the existing one. You can find them on Ebay. Search for R004 resistor. You need a 3w one for 25A, but if you stack one over the other, 2W or less would be OK, as it will only take 20% of the current.
 
Thanks D8veh. If I want to stack on top and increase the 15a current by more than 20%, say, to go up to as high as a 250w CST 180mm can usefully use, which resistor would that be? Apologies - it's an area I don't yet understand.
 
This is where it gets complicated. Your motor will perform well at 22 amps, but your controller might get hot. Which controller is it? Most 15A ones can go to 18A, but after that, heat is a problem. The formula is Ra = (Rs x Rt)/ (Rs-Rt), where Ra is the added resistance, Rt the new desired total resistance, Rs is the original shunt resistance.

22 amps would mean the new resistance would have to be 15/22 × .005 = .0034

Ra = (.005 × .0034)/(.005 - .0034) = .0106.

You would therefore add a 010 resistor. It would take 1/3 0f the current, so it would dissipate 7 x 7 x .010 = .49 watts, so you need one about 1 watt or more.
 
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