Is the battery to blame?

[MarkCR750]

My winter hack, a 1991 CBR1000f died on me at the lights recently in neutral, the starter wouldn't spin the engine and the neutral light just dimmed when I pressed the starter button, the bike bumped started easily though so I got the 10 miles home OK, once home it would start on the button , since then I've charged the battery and it's seemed OK for a couple of weeks, a little sluggish on the starter at times, today it cut out at the lights again but started (just) on the button, once home I got the multimeter on it and it showed just over 12v, I started the bike and got 13.5v at 2500 rpm, I switched the lights on and it dropped to under 12v with the engine running!, (I always ride with headlights on btw), the battery was fitted by the previous owner and is relatively new but is a cheap lead acid one, before I splash out £55 on a decent motorbatt battery I thought I'd ask for a second opinion, do you think the battery is the culprit?, cheers Mark.

[mike the bike]

Sounds like.  I remember at a tyre dealers that also sold batteries,  They had a piece of test equipment that was, basically, a dead short.  The idea was to short the battery for a few moments then measure the voltage- checking that it recovers. 
It sounds like yours doesn't.

[haynes66]

i would say that the problem is stopping at the lights. just keep going!!

[3scs]

Don't try this at home I was shown by an old school auto lecy get a set of jump leads connect to battery also connect a multimeter to battery terminals stand AS FAR AWAY from battery as possible wear a pair of goggles short battery for a short while if battery voltage drops below 9.6 it's shot do it outside though not in garage

[K2-K6]

The alternator should be able to get above 13.5volts at those revs even with the lights on.

A healthy and charged battery should sit at about 12.6 to 12.9 ish, any alternator output below that range would not really charge the battery.

If you gave the battery a long slow charge for 24hr then record the voltage,  then after a week check voltage again, it should be more or less the same. Anything more than 0.2 0.3 ish drop in volts would indicate that it's not that healthy.

You can do an earth system check, start and run motor and switch lights on,  raise revs to about 2500rpm, measure between bat negative terminal and alternator casing, it should be less than 0.1volts. If it's much greater than that it would indicate that the earth's need attention.

Also that era of bike can have I think voltage reg reporting affected by the kill switch so make sure that's all clean and functioning properly.

[Menno]

There is a very easy way to check whats wrong.
And it is safe as well....

Start your bike.
Let it idle.

Disconnect your battery from the bike while idling.

If the bike dies immediately when you pull the cable it is likely to be your altenator or regulator.
If the bike keeps running it is defenately not your altenator or regulator and you could say it comes down to your battery.

check:
https://youtu.be/xF6WUvqC1Xc

[Tomb]

Do you have heated grips?

14V would be better than 13.5v when revving to 2500, so charging is a little down, and IF running extras like heated grips could just overwhelm the charging,

If your bike starts Ok when you get it out for the ride its sounds like your battery is adequate, then runs Ok until ticking over at the lights, I'd be looking at charging first. And rec/regs are a known week point on the CBRs, I've changed a few on CBRs. They can be had for as little as £6 on ebay from China, if you buy them buy two and mount them on a BIG heatsink and side by side so when the first one fails you can simply swap the connector to the next. Or buy 1 quality replacement.

[MarkCR750]

Thanks for the replies, apologies the results I previously posted were misleading, I got some better results today, working in the light taking my time etc, so 14.7v at 3.2k revs 12.5v at 1.2k lights off, --------------11.75v at 1.2k, 11.8v at 3.2k lights on. So it looks as though the alternator is good but when the lights are on they taking a lot of voltage!, could this be a battery fault ? (Electrics as you can tell are not my thing).
I.e it appears to charge fine until the lights are switched on.

[Bryanj]

not normally, alternator or regulator fault

[kevski]

If you have checked all of your connections and earths, with this bike at 3.2krevs with everything on you should be getting a full 14v back to the battery, 14.7 with nothing on is getting on for 15v and that shouldn't be happening, this will kill the battery, what would help is a battery that is known to be good then all connections checked with a meter for resistance, if this all checks out, check the voltage coming from alternator before it gets to the reg/rec, if that checks out ok move on to the reg/rec, from what you have already posted i would be looking at the charging system.

[3scs]

Another way to check battery connect meter to batt terminals switch lights on and start up again a reading of less than 9.6 v battery is shot

[MarkCR750]

thanks for the advice all, I'll order a new reg rec and try the battery from my CR when I've got the new reg rec fitted.

[Greebo]

Mark

I have got a acid battery which i took off my 2013 RE GT it had only done 500 miles [ I put a motobatt on it]
its in perfect condition but not sure if its any good for your bike... you can have it for Free & try it if you want to have a run up to mine.

Cheers
Greebo

[MarkCR750]

Thanks Graham but I just checked and it too small re AH for mine.

[gtmdriver]

I have the workshop manual for my CB350F and these are the testing figures for the charging circuit.



I would imagine the figures for the 750 would be similar.