Charging System Quick Test Results and Queries

[bill_face]

Hello.

I've got a 1979 GS550 that has been having some charging problems.

I've replaced the original R/R with a SH775 bought from forum member Nessism and cleaned up / replaced terminals in the charging circuit but not the whole electrical system.

I've fitted Dyna-S ignition and done the coil relay mod.

I haven't been far, but it does seem to be charging but give some below-expected results at some stages:

1) Key Off(12.7-12.9): 12.4V
2) Key On(12.2-12.5) : 11.8V
3) At idle(12.6-13.2): 12.8V
4) At 2500rpm(13.5-14.0): 13.7V
5) At 5000rpm(14-15): 13.8V
6) Key Off(slightly higher than 1):12.7V

The numbers in brackets are the expected voltages from Mr. posplayr's Quick Test. The other numbers are my results.

So the first thing is the initial voltage is a bit low, but this has come straight off the charger. My charger is an Oxford Oximiser 900, that seems to charge it right up and then maintain it by draining and then charging it again.

Then the Key On result is way low, and it does struggle to start from cold, which may be explained by this. Thereafter the results seem alright.

I'm guessing the answer may be to buy a new battery, but I've already bought 2 in the last 10 months. I haven't been using the bike often as it been in bits, which may explain battery depletion but would like to be sure I need one before splashing out again. Does the fact the Key On drops so far indicate a weak battery? Are there any other tests on battery strength I can do without a hydrometer?

Also when I turn my headlight and sat nav on the voltage drops to around 12.2 at idle. Is this normal? I have chopped the headlight connection from the stator out of the equation as suggested by someone here on an earlier thread. Ideally, I'd like to have the headlights on most of the time to aid visibility.

 

[fastbysuzuki]

The Oxford charger does not drain and charge, under normal conditions it float charges ( cuts off when 14.5 v reached and keeps it that way) if you have cleaned and checked all the connections for tight fit in the charging system given your readings on 1 =12.4v is this after the charger has been disconnected?
If so then either the battery is poor or the charger is not working correctly. If the charger is working then the battery is not taking the correct charge are you buying decent ones? But given all you readings the battery is not going to last on the bike you need to get over 14v preferably 14.5v at 5000rpm
Have you done the stator test yet? Sounds like it's going down given the info you have provided.

 

[Steve]

One other thing to keep in mind: all your numbers seem to change about the right amount in the right direction, but seem to be a bit low. Have you checked the accuracy of the meter? Maybe try those same tests on your car or check the numbers against another meter. If the numbers are different than the other meter, you will then have to find yet another meter, then decide which meter to believe.

.

 

[bill_face]

Thanks for the input.






thanks for the input. Firstly another question: how long should a good battery hold a charged voltage. Say you get it home from a ride and it reading 12.8V Should it read the same 24hrs later?

In response to the above points:

My readings are probably around 0.2V low, I bought a cheaper volt display that I could leave hardwired to the battery with a switch so I could do this stuff more easily. I did check it against my voltmeter, but at lower voltages (nearer 12 there is a discrepancy)

12. 4V was after the charger was disconnected. To be fair I had left it a while after disconnecting. I've tried reading the voltages with the charger connected, and it seems to do the following:

-on start up it enters bulk charge mode where the voltage rises quickly from around 13V to around 14.5V (takes a minute or so)
-then it flicks into maintain mode, where the voltage drops back down to about 13V and very slowly rises back towards 14.5V (I haven't watched it the whole way as this takes around an hour), it seems to repeat this cycle. So you could come to take it off charge anywhere between 13V & 14.5V

 

[posplayr]

The voltage across the battery rises when you push current into it. For lead acid , At 14.5 volts you have nominally C/5 . charging. C is the amp-hr rating on the battery. C/5 would be 14/5 or just under 3 amps charging current. Is the resting voltage is 12.8 volts (no charging) the a first approximation is C/10 at (14.4-12.8)/2+12.8 (mid point)=13.6 volts.

to tell is a battery is holding a charge you put a known load on it and see how much voltage you are dropping. You do not use testing voltage.

 

[Steve]

Are you using a wet-cell battery or a sealed AGM battery? The "full-charge" voltage is just a little different.

A wet-cell battery (there are caps on top, and you have to add electrolyte) is fully-charged at 12.6 volts. If you measure the voltage right after removing the charger, you will likely see about 12.8, but wait an hour, or turn the key ON for about 10-15 seconds, it will drop to 12.6. Because of different lead alloys in the plates, a fully-charged AGM battery will be at 12.8 volts, with a "just-off-the-charger" voltage close to 13.0. If you are not seeing those voltages, I would really suspect the battery condition. You did say that you have replaced it a couple of times in the last few months, which also leads me to question the charging system. If a battery is not charged properly, it will degrade rather rapidly.

How long should it hold that number? Let's just say that it should not drop more than a couple of tenths of a volt in a month. That is after the surface charge is removed.

.