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Voltage drop - how much is normal...

59 Views 0 Replies 1 Participant Last post by  NorthCust
After a long cross-country trip the other week where I realised my battery died and had to race against it dying on me (officer) I put the spare battery I had in, but I was noticing what seemed like quite a significant voltage drop.

So with a freshlycharged battery I'd see 12.7v at the battery but as soon as i turn the key (not start just light up the panel etc) I was seeing it drop to 12.1 or thereabouts...

I guess fuelled by paranoia from that trip I figured the spare battery much be bad sinc eit's been standing a while. I bought it but then never needed it, and bought yet another new battery.

However the new battery also registers a voltage drop so yesterday I went through and pulled all the fuses one by one to see where to start looking for problems. I have a bunch of extra sensors and stuff on mine so it could be any number of things I've added (e.g. relay for heated grips, temp sensor, indicator repeaters etc) but it seemed to be mostly from just the instrument panel and side lights, both of which seemed ot be on the same fuse ("signal").

On the new battery (measured at the battery, freshly charged) I was seeing ~12.7v and with the ignition on it was dropping ~0.5v to ~12.1/12.2. I'm pretty sure I haven't messed with anything on that part of the loom so got wondering whether other people get the same drop.

Some of it will be due to power attenuation through the cable.. measuring the voltage a metre or so away vs on the battery will show a bit less just from that, but then speedo, side lights etc.. it seemed plausble but Idk why I never noticed it before.

So my question is if anyone else has a multimeter could they please try running the bike for a couple of mins so it's charging (~13.7v), then measure the voltage directly off the battery with ignition off (should be around 12.7) and then measure the voltage off the battery again with the ignition on but engine not running (fuel pump primes and then thigns settle... thats the reading I'm after).

0.5v doesn't seem like an unreasonable voltage sag for the tacho and side lights but I'm just confused that I never noticed it before so would like to double check my maths as I'm plannign to do some longer trips and would like to know it's all tip-top..

My on-bike voltmeter is on the front fairing stay so I see it when I get on the bike but dont get distracted by it while riding, and there's likely to be some attenuation just from skinny cables .. which if you allow say 0.1-0.2v means the actual voltage sag from the "signal" loom is probably less than 0.5v.. which doesn't seem unreasonable for a tacho and few lights...but can anyone else please confirm whether they see similar?

Thanks in advance :)

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