Battery testing

[nb celestine]

I,m going to charge the batteries up to float tomorrow and then check the SG.

 

How long do I have to leave them before I do the test?

 

The SG should be 12.7. Is that correct? Cheers, Paul.

[by'eck]

I think you may be confusing a fully charged 12 volt lead acid battery voltage of about 12.7 volts with the equivalent SG which will be around 1.26. Wait about 20 minutes before checking after charge.

 

BTW be careful of using the SG abbreviation on this forum. The SmartGauge fan boys have a copyright on it

[nb celestine]

I think you may be confusing a fully charged 12 volt lead acid battery voltage of about 12.7 volts with the equivalent SG which will be around 1.26. Wait about 20 minutes before checking after charge.

 

BTW be careful of using the SG abbreviation on this forum. The SmartGauge fan boys have a copyright on it

 

Hi Richard, Your hydrometer must be different to mine. I,ve just dug mine out and it shows a green band between about 12.65 and 12.9.

 

Thanks for the 20min advice.

[ChimneyChain]

A quick question regarding batteries. At work we use a drop tester and that tells us straight away if the battery is good or not. I suggested using this method to someone who wanted to test his batteries and he almost died of heart failure. He said you can't drop test leisure batteries, but he didn't give me an explanation as to why. Can anyone enlighten me please.

 

Darren

[Ark Right]

Hi Richard, Your hydrometer must be different to mine. I,ve just dug mine out and it shows a green band between about 12.65 and 12.9.

 

Thanks for the 20min advice.

 

Hi, the decimal point is definitely in the wrong place, you should be looking for around 1.28 SG when charged.

Cheers

A

[Pentargon]

A quick question regarding batteries. At work we use a drop tester and that tells us straight away if the battery is good or not. I suggested using this method to someone who wanted to test his batteries and he almost died of heart failure. He said you can't drop test leisure batteries, but he didn't give me an explanation as to why. Can anyone enlighten me please.

 

Darren

On the basis that what you call a "drop tester" is what I know as a "Heavy discharge rate meter" and the test involves bridging the poles and sparks then the answer is emphatically NO A starter battery is designed to have a high rate of discharge. It has to be able to twirl over an engine. The inside is built differently from a "Leisure" battery which is desinged to release small amperages over a very long time. Using a "Heavy discharge rate meter" on a leisure battery would lead to rapid heating of delicate plates and at the worst possible scenario an explosion scattering lead acid over an area much bigger than a typical engine room or garage.

 

Your work practice will be for starter batteries, Darren am I right?

[Ark Right]

A quick question regarding batteries. At work we use a drop tester and that tells us straight away if the battery is good or not. I suggested using this method to someone who wanted to test his batteries and he almost died of heart failure. He said you can't drop test leisure batteries, but he didn't give me an explanation as to why. Can anyone enlighten me please.

 

Darren

 

Hi Darren,

Drop testers are an aid for measuring the capacity available from cranking batteries (starter batteries) which are designed for short sharp bursts of power. A leisure battery is designed for slow discharge over a long period, a Drop Tester puts a high load (depending on size of the tester) direct to the battery, not something you would want to do to a leisure battery.

Erm hope that makes sense

Cheers A

[by'eck]

Hi Richard, Your hydrometer must be different to mine. I,ve just dug mine out and it shows a green band between about 12.65 and 12.9.

 

Thanks for the 20min advice.

 

Here's some more - it won't take 20 mins to read

[ChimneyChain]

On the basis that what you call a "drop tester" is what I know as a "Heavy discharge rate meter" and the test involves bridging the poles and sparks then the answer is emphatically NO A starter battery is designed to have a high rate of discharge. It has to be able to twirl over an engine. The inside is built differently from a "Leisure" battery which is desinged to release small amperages over a very long time. Using a "Heavy discharge rate meter" on a leisure battery would lead to rapid heating of delicate plates and at the worst possible scenario an explosion scattering lead acid over an area much bigger than a typical engine room or garage.

 

Your work practice will be for starter batteries, Darren am I right?

 

Hi Pentargon, yes i regularly test HGV batteries at work so what you said makes sense. A young apprentice did drop test a set of batteries straight after They came of charge

( like a dick ) and did blow the battery and him sky high, he was fine though but it did create much laughing and piss taking.

Thanks for the reply.

 

Darren

[Pentargon]

Hi Richard, Your hydrometer must be different to mine. I,ve just dug mine out and it shows a green band between about 12.65 and 12.9.

 

Thanks for the 20min advice.

 

Celestine. Your hydrometer is "How can I put this inoffensively?" less than professional in hydrometer terms but will indicate voltage after a fashion. A 'real' hydrometer measures the Specific Gravity of a liquid as compared with water. The results are read out either side of the benchmark SG for pure water which is 1.000. Battery testers are built on the principle of real hydrometers to indicate the SG of the electrolyte. But they present their results as VOLTS. As a battery discharges, the density of the electrolyte goes down. The less dense the liquid is the lower down the weighted float drops in the electrolyte which is why the RED is at the top and the green is at the bottom. I can't tell you the SG of battery acid at different voltages but the subject was a whole semester at college 50 years ago. It's the bottom end of rocket science. Do follow RichardHula's link above at post8. esp. the bit about adding and subtracting differentials over and under 25C. It's quite good

Edited December 17, 2011 by Pentargon

[bizzard]

To be honest i think a lot of boaters are already unbeknowingley continually giving their batteries a pretty hefty drop test with all the huge inverters and high powered appliances they use and so for the same reason their batteries don't last very long.They'd probably be better off with starter batteries as long as they keep them well charged up to say at least 70%.

[ChimneyChain]

Hi Darren,

Drop testers are an aid for measuring the capacity available from cranking batteries (starter batteries) which are designed for short sharp bursts of power. A leisure battery is designed for slow discharge over a long period, a Drop Tester puts a high load (depending on size of the tester) direct to the battery, not something you would want to do to a leisure battery.

Erm hope that makes sense

Cheers A

 

Hi Ark Right. Sorry only just seen your reply. Thanks for the explanation.

 

Darren

[Tony Brooks]

Hi Ark Right. Sorry only just seen your reply. Thanks for the explanation.

 

Darren

 

 

Another problem is that drop testers need a discharge of about three times the battery's Ah rating BUT starting batteries that can definitely be drop tested are now rated in CCA with no reliable conversion factor to give Ah. All the drop-testers I have seen over the last few years are also rated in CCA, either fixed or adjustable and any drop-tester an ordinary boater is likely to get hold of will probably be for cars so for a battery capacity of about 40 Ah (but rated in CCA).

 

Seeing Gibbo has stated on more than one occasion, and invited battery manufacturers to sue him, that many so called leisure batteries are in fact constructed as starting batteries it should be OK to drop-test them as long as the tester is matched to capacity. They should have a dual rating (CCA & Ah).

 

Another "problem" is that the batteries need to be well charged to give reliable results. It was not unknown for a "free" battery test to be offered with no attempt to ensure the battery was charged. The result was a lot of "failed" batteries as far as the customer was concerned and a load of batteries for friends cars once charged and tested properly.

 

Stick with a hydrometer (observing the precautions re toping up and charging) because it will easily show faulty cells and as an every day check use a good quality voltmeter whilst cruising by taking a measurement a little while after you shut down for the day.

[ChimneyChain]

Another problem is that drop testers need a discharge of about three times the battery's Ah rating BUT starting batteries that can definitely be drop tested are now rated in CCA with no reliable conversion factor to give Ah. All the drop-testers I have seen over the last few years are also rated in CCA, either fixed or adjustable and any drop-tester an ordinary boater is likely to get hold of will probably be for cars so for a battery capacity of about 40 Ah (but rated in CCA).

 

Seeing Gibbo has stated on more than one occasion, and invited battery manufacturers to sue him, that many so called leisure batteries are in fact constructed as starting batteries it should be OK to drop-test them as long as the tester is matched to capacity. They should have a dual rating (CCA & Ah).

 

Another "problem" is that the batteries need to be well charged to give reliable results. It was not unknown for a "free" battery test to be offered with no attempt to ensure the battery was charged. The result was a lot of "failed" batteries as far as the customer was concerned and a load of batteries for friends cars once charged and tested properly.

 

Stick with a hydrometer (observing the precautions re toping up and charging) because it will easily show faulty cells and as an every day check use a good quality voltmeter whilst cruising by taking a measurement a little while after you shut down for the day.

 

 

Thanks tony very much appreciated.

 

Darren

[nb celestine]

Here's some more - it won't take 20 mins to read

 

Thanks Richard, you were right. My hydrometer hasnt got a decimal point between the numbers. It just reads 1265- 1290.

 

Looked at the site above but lost the will to live when it described how to build a SIMPLE battery desulphator.

 

I,m a builder by trade. I think I,ll stick to building houses. Regards, Paul.

[WotEver]

... I can't tell you the SG of battery acid at different voltages...

Very approximately (depends on lots of variables including temperature)...

 

SoC____SG_____Voltage

100%___1.265__12.7

75%____1.225__12.4

50%____1.190__12.2

25%____1.155__12.0

0%_____1.120__11.9

 

Tony