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Author Topic: Voltage drop caused by solder?  (Read 368 times)

Offline freemonty

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Voltage drop caused by solder?
« on: Jul 06, 2017, 15:24:57 »
Shop manual says should be 14.5 volts at the battery across the rpm range, but I'm getting high 12s at idle and low to mid 13s at higher rpm. I had to make a repair to 2 of the 3 wires from the stator that involved soldering new connections. My question is could the repair be causing the voltage drop if I didn't do something correctly? Or should I be looking elsewhere?

Bike is 76 KZ400 with an aftermarket solid state voltage regulator and the problem stems from switching to a new Lithium ion battery. The repair has worked for years and kept my agm lead-acid battery charged just fine with the ~13v readings, but the lithium seems to be more finicky and Tuesday I was left stranded when the lithium went completely dead.


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Online Sonreir

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Re: Voltage drop caused by solder?
« Reply #1 on: Jul 07, 2017, 11:17:22 »
I think you might be facing multiple issues.

I doubt even a bad soldering job would cause that much of a voltage drop, but some is to be expected. Any time you join or splice wires, there will be a little drop, but not as much as you're seeing.

That said, I'd get a new battery (lead acid). Once LI-ION goes dead, it's usually dead for good (unless your manufacturer has specific internal electronics to help with this). When LI-ION drops below a certain internal voltage (about 2.2V per cell on a 12V battery), the copper anodes begin to dissolve within the electrolyte. This is permanent damage and will prevent the battery from being used again.

Anyway... like I said.. get a lead acid battery into your bike and run your tests again. If you're getting good voltage readings from your lead acid battery, you should be getting the same (or actually lightly higher, at rest) on a LI-ION.

Finally, make sure your LI-ION has enough cells. It's common for people to stick the smallest LI-ION they can find onto their bike and this can sometimes cause problems on vintage machines. Old bikes don't always make usable wattage at low RPM, so if you idle your bike for a while (initial testing and setup after a build?) or do a lot of city riding (where your RPMs aren't staying in the mid-to-upper ranges) then you might be running from the battery and not the alternator. While LI-ION have great cranking power, their capacity is much lower than lead acid, usually. Usually about 25% of the lead acid rating (12Ah PbEq on LI-ION is really more like 4Ah on a lead acid battery).
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Offline freemonty

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Re: Voltage drop caused by solder?
« Reply #2 on: Jul 07, 2017, 20:00:22 »
@sonreir Manufacturer doesn't list # of cells but I am getting 9.5v. Is there a way to know the cell qty? So I can see if this thing is worth saving and if it was enough for my bike to begin with? I went direct replacement rather than trying to downsize so I don't think that'll be an issue but obviously I'd like to try to save my $150 paperweight if possible.


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Online Sonreir

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Re: Voltage drop caused by solder?
« Reply #3 on: Jul 07, 2017, 21:12:37 »
Any 12V battery will have a number of cells divisible by four. 9.5 is not good news. Put it on the charger overnight and let the battery sit for another 24 hours (off the charger). Take another measurement. If you're not over 13V, your battery is dead for good.
Sparck Moto - http://www.sparckmoto.com

Audaces fortuna iuvat.

1977 Honda CJ360 - Café SOS - Stage One™, Café SOS - Stage Two™
1976 Puch Maxi - APuchalypse Now
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