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Discussion Starter · #1 ·
Hi,

I have a stock CB350 K3 that i believe is draining the battery when not in use. After a week of sitting a fully charged battery can drop to around 11V.

I have disconnected the ground from the battery and measured with a voltmeter 12V between this cable and the -ve battery terminal in the off position. I have also measured 0.4-0.5A with my ammeter.

Is there a likely candidate for parasitic draw, such as the rectifier, and if so what cable would be priority to check? Or could it be anything and the only way is to crack open the headlight bowl and just go through pulling apart each circuit until the readings disappear, or change?

I’m guessing it could be the culmination of a few smaller draws that have added up to a big enough drain to run the battery dry?

Thanks for your help!
 

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I think it's possible the rectifier could be the culprit, as they have been known to degrade in function over the years and break down in the diode function. If you haven't yet, you should replace the rectifier and regulator pair with a modern rec/reg combo unit. Sparck Moto sells one that will plug right in as I understand it, and I believe they are a site sponsor as well

12V Single Phase Regulator/Rectifier - Sparck Moto

https://www.hondatwins.net/forums/114-sparck-moto/107081-sparck-moto-offerings-honda-twins.html
 

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Discussion Starter · #3 ·
Thanks for the reply! I thought the rectifier may be the culprit. I was going to disconnect it and see if the voltage reading stops. If my memory serves me I think it is the red and white cable from the battery to rectifier?

Also, I have CMC one on another CB350 k4, which I may swap to see if there are any changes.
 

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Just unplug the entire plug going to the rectifier (4 pins if memory serves?) and that will take it out of the equation. as long as the CMC unit is a plug/unplug, you won't have to modify anything to check it. FYI, the Sparck Moto unit is cheaper than the CMC unit
 

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Discussion Starter · #5 ·
Thanks ancientdad. The cmc rec came with my other 350 but I prefer the Sparckmoto one. Have seen Sonreir discuss on the dotheton forum if I remember rightly. Would have to pay a few extra quid to get it past customs, but there’s no UK based alternative AFAIK?
 

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Not at this time, but if you're interested in being our UK distributor, please let me know. ;)

For the full testing of the parasitic draw, grab a multimeter and then disconnect the negative terminal of the battery.

With the ignition switch turned off, measure current between the negative terminal of the battery and the ground strap. With no draw, you should get a zero on the meter. Any other number indicates you do have a parasitic draw.

So first, let's assume no draw. The most likely issue at this point is your battery. Either the electrolyte fluid is low (assuming flooded cell lead acid battery, like what originally came with the bike), or the battery is nearing the end of its lifespan.

If there is a draw, things start getting more complicated. 99% of the time, the culprit will be the regulator/rectifier. Unplug the unit and repeat the current test. If you're still getting draw, you're in for a long set of tests. Start working your way along the solid red and red/white wires. You're looking for anything that's connected to them (solenoid, ignition switch, fuse, etc) and you'll want to start unplugging things until you can get a zero amp reading from the battery-to-ground test. At this point, you're possibly looking for intermittent shorts in the wiring or other abnormalities...
 

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Discussion Starter · #7 · (Edited)
Not at this time, but if you're interested in being our UK distributor, please let me know.
I would be interested (I already have an internet retail business) but the issue would be that I would end up using all the stock on my own bikes. Been drooling over one of you universal flasher relays for my 6V CG125!
 

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Discussion Starter · #8 ·
Thanks for the advice Sonreir! I did do that test and was getting 0.5A or thereabouts. It fluctuated a bit.

I have the day off tomorrow so will try again with the rectifier disconnected, and follow your instructions if no change. I’ll post my results. Cheers.
 

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Discussion Starter · #11 ·
So, I stuck a fully charged battery on the bike and put the tester between the ground cable and negative post. Was getting 0.5-0.6A of current flow, and the same voltage reading as I was getting with the battery disconnected. I unplugged the rectifier and the readings stop. No current or voltage. Pretty conclusive.

Need to wait until the Christmas spend and hectic postal rush is over, but it looks like a replacement rec is on the cards. Meanwhile i’ll have to disconnect the ground after each ride.
 
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