Help with battery testing

[lyralicious]

I know this is probably really simple, but I just can't find the answer anywhere, and hoped someone could help.

We have 2 sets of 2 x wet cell 6v batteries (each set is connected in series to give us 12v, then both sets are connected in parallel).

It is my job to regularly check the voltage and SG (I do this every fortnight). Up until now the SG readings have remained between 1235 - 1250 (we are in the tropics). Today my hydrometer float is almost on top of the acid, showing a reading above the highest (1300) measurement. What does this mean? Could it be right? Could the hydrometer be broken?

If the reading is right, what do I do? All the information I have tells me what to do if the reading is low, but I can't seem to find anything that tells me what to do with such a high reading.

I have checked the voltage, which is 12.7. There is plenty of acid covering all the plates.

I am using a basic hydrometer purchased locally here in India.

 

[nimbusgb]

Is it particularly cold in India at the moment? Had you just topped up the batteries or had they not been on charge for a long while? Although the plates are covered is the level the same as usual or 'a little low'? Did you forget to rinse out the Hygrometer last time you used it?

 

[Plevier]

Something doesn't add up. (I would suspect a slight leak in the hydrometer float first. EDIT - DISREGARD - that's the wrong way round, sorry, silly slip!)
SG of around 1250 makes sense for tropical conditions. 1300+ is too high anywhere but it can't have appeared by itself. Are the batteries very short of water (edit - sorry you covered that!), or have they been topped up with acid not water? I doubt it as you are obviously following a careful regime.
Genuine SG of 1300 would give an OC voltage of 12.9 even at 25 deg C, higher if your ambient is higher. 12.7 is consistent with SG of 1260-1270 depending on temperature. (You need to make these measurements very carefully to be meaningful.)
Try another hydrometer.

 

[lyralicious]

To answer your questions:
The temperature is mind-boggling high in India, as is the humidity. But we have a/c below, and the temp is about 27 degrees, the same as it was on previous testing days.
The batteries have been on permanent charge, through our battery charger, as on previous testing days.
The level is the same as on previous occasions.
The batteries are only three months old and have not yet needed topping up.

Am worried I may not have washed the hydrometer properly last time. How can I tell if there is a leak in the float?

I hope it just means I need a new hydrometer.

 

[Dave_Seager]

A leak in the hydrometer float is unlikely to make it float higher so I think that you can rule that out. It might be worth buying or borrowing another hydrometer to check though.

According to information I found at http://www.engineersedge.com/battery/specific_gravity_battery.htm, your readings are not wildly abnormal although it is hard to see why they should have changed as they have.

 

[Plevier]

A leak in the hydrometer float is unlikely to make it float higher so I think that you can rule that out.

Yes, sorry I just realised I'd got that the wrong way about and logged on to correct. A leaky float would under-read.
It's harder to explain an over-reading hydrometer but I still say, try another one first of all. Not washing it last time wouldn't matter.
I stand by everything else I said.
I suppose it's just possible that your batteries should have 1300sg but have never been fully charged before, but it seems unlikely, such a high sg is unusual and would be unwise for an installation of this type. (That's my view based on years in the battery industry anyway!)
I see they are only 3 months old. What are they? Who filled and commissioned them? If not the factory, dealers are very prone to not doing commissioning charge thoroughly. Is there no documentation saying what the sg should be?
Your OC voltage reading does not really indicate sg of 1300 or above.

Are you the same boat as demonboy? Are these the Exides?

 

[alahol2]

I had a cheap hydrometer at one time. The scale was printed onto a sheet of paper which was fixed in the float by a bit of glue. It always struck me as highly likely that at some time the glue would fail and the scale 'move'. Any chance that yours is like this?

 

[lyralicious]

Yes, this is a cheap hydrometer with the piece of paper wrapped round as you describe. The only bit of the float still in the water is the bulbous bit at the bottom, where the paper finishes at 1300, and the makers name is printed.

I'm getting a new one on Friday and if the problem persists I'll be back. No disrespect to anyone, but I hope I'm not on here again with this problem!

Thanks for all the helpful advice.

 

[rob2]

Ready to be shot down in flames... You say the battery is on constant charge? Most people advise that the battery shuld be rested (no charge or discharge) for some hours before testing. Could it be that the charger was on a different cycle to that expeerienced on previous tests? I believe this can affect the voltage readings, but not sure about SG,

Rob

 

[Plevier]

I believe this can affect the voltage readings, but not sure about SG,

Rob

A battery just off charge will show an artificially high voltage for a while but it won't affect the sg.

Might be an idea to shake the float and see if the paper scale moves!

 

[Marsupial]

float the hydrometer in ordinary water - see what it thinks the SG of water is - should be 1 (1000) if its over then something is wrong with it.

 

[nedmin]

Why not get a reading of distilled water it should be 1.0 that will tell you is your hydrometer is reading right.

 

[Plevier]

Did you go for the Exide 6C 225 golf cart batteries in the end?
If so they are specified as electrolyte filling sg on commissioning 1.255 which will become 1.280 when fully charged. Both specified at 30degC.
In other words it's supplied dry charged, not factory commissioned, but in that condition it won't be fully charged just by filling with acid, it needs commissioning charging to develop it.
I haven't been able to find their commissioning charge procedure. Typically however it's a voltage limited constant current charge for 24hrs or so - i.e. something similar to a boost/equalisation charge regime but a bit more strenuous - followed by adjustment of sg to the correct final value.
If yours were not properly commissioned initially by a distributor, a common problem - they can't be bothered or don't understand its importance -, then initially they wouldn't have been fully charged. If since then you have gone through a few boost/equalisation charge cycles - I don't know what your charging system is - you may in effect have completed the commissioning charge developing more capacity and increasing the sg.
If you prove that your sg now really is 1.300 or above I think you should take it up with the supplier if possible.
It should be adjusted down a bit for best life.
With luck it will just be the hydrometer!

PS I've never seen a battery hydrometer that will read down to 1.000 so calibrating with distilled water is probably not possible. You could carefully make a salt solution of known sg to calibrate it. 36gms of salt dissolved in 100gms of water will I believe yield a saturated brine with an sg of 1.200 at 20 deg C. I've never tried it though!

 

[Alex_Blackwood]

To answer your questions:
The temperature is mind-boggling high in India, as is the humidity. But we have a/c below, and the temp is about 27 degrees, the same as it was on previous testing days.
The batteries have been on permanent charge, through our battery charger, as on previous testing days.
The level is the same as on previous occasions.
The batteries are only three months old and have not yet needed topping up.

Having looked after batteries all over the globe I have never come across batteries, new or otherwise that would, under the parrameters listed above, not need topping up at least every couple of weeks. If not more frequently!
I suggest you take them off charge and have a very close look at the levels,and again after a couple of hours. I think they may well be overcharged. Hope I am wrong.

 

[Plevier]

Having looked after batteries all over the globe I have never come across batteries, new or otherwise that would, under the parrameters listed above, not need topping up at least every couple of weeks. If not more frequently!
I suggest you take them off charge and have a very close look at the levels,and again after a couple of hours. I think they may well be overcharged. Hope I am wrong.

I can't agree with that without qualification.
If they were frequently discharging and fast recharging, OK.
However if this vessel is in port and on mains as I understand, and the batteries are being maintained on float charge with little cycling in a constant air conditioned temp of 27 degrees as stated, they shouldn't need topping up anything like 2 weekly.
3 months may be pushing it to the other extreme - OP says there is plenty over the plates but it is worth another look.
I'm a bit puzzled by the suggestion of overcharging, if they were being constantly overcharged they would certainly be short of water by now or long before. Unless you mean sudden recent overcharge due to a fault.
It would be helpful to know the charger voltage settings and actual measurements.

OP - Do the batteries have clear indicators for the correct level e.g. a pointer below the filler or is there a manual specifying a depth above the plates?

Whatever the cause, if sg of 1300 is confirmed, it should be reduced. There may be enough space to do it just by dilution, or it may need a bit of acid removing. Adjusting gravity isn't that straightforward, you have to ensure thorough mixing (not a problem at sea!)