Home-made battery checker.

MM5AHO

MM5AHO

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I should change at least one of my boat batteries this year, maybe more.
I date mark them, but that doesn't guarantee that the oldest is the worst.

Can I devise a home made battery checker to decide from the three batteries which should be changed? Something that measures volt drop under a reasonable (say 20A) load perhaps? Suggestions?
 
MM5AHO said:
I should change at least one of my boat batteries this year, maybe more.
I date mark them, but that doesn't guarantee that the oldest is the worst.

Can I devise a home made battery checker to decide from the three batteries which should be changed? Something that measures volt drop under a reasonable (say 20A) load perhaps? Suggestions?
Click to expand...

Why should you change one or more of the batteries ?

If you have good reason to suspect one or more are no longer functioning correctly, carry out the usual battery tests on each battery and change any that are not up to scratch. If all are the same age and have been subjected to the same charge/discharge regimes, it might be worth considering changing the whole bank.
 
MM5AHO said:
I should change at least one of my boat batteries this year, maybe more.
I date mark them, but that doesn't guarantee that the oldest is the worst.

Can I devise a home made battery checker to decide from the three batteries which should be changed? Something that measures volt drop under a reasonable (say 20A) load perhaps? Suggestions?
Click to expand...

I did this years ago with a high-beam lamp as a load and two multimeters, one set to V the other to A. And a basic webcam set up to take a picture every 10 minutes. I let it run overnight, and then plotted the values in an Excel sheet. Finding the best webcam app to use was the main issue back then as as recall.
 
I have three 55Ah batteries. They're set up in a bank of two and a single. They are 2005, 2007, 2009 vintage. Not bad life I think! One of the pair doesn't hold a charge so well, but I haven't poked about to determine which. If I start poking about in there, I should test them all and see what I'm facing, or at least plan what to do over the winter.

I could do that time delayed picture idea, use a Gopro or similar. I'd thought of a heavier current for shorter time.
 
MM5AHO said:
I have three 55Ah batteries. They're set up in a bank of two and a single. They are 2005, 2007, 2009 vintage. Not bad life I think! One of the pair doesn't hold a charge so well, but I haven't poked about to determine which. If I start poking about in there, I should test them all and see what I'm facing, or at least plan what to do over the winter.

I could do that time delayed picture idea, use a Gopro or similar. I'd thought of a heavier current for shorter time.
Click to expand...

I'm not sure how your batteries are connected Geoff .... presumably two in parallel and one separate start battery, but as, you say, they owe you nothing.

Since connected batteries produce best results if they are identical in model and age, and you don't want to replace all three, I would use the newest battery as the start battery and replace both the oldest two. Provided you have a way of using the house batteries as a start battery (switch or jump leads), this should be a low-risk option.

Richard
 
RichardS said:
I'm not sure how your batteries are connected Geoff .... presumably two in parallel and one separate start battery, but as, you say, they owe you nothing.

Since connected batteries produce best results if they are identical in model and age, and you don't want to replace all three, I would use the newest battery as the start battery and replace both the oldest two. Provided you have a way of using the house batteries as a start battery (switch or jump leads), this should be a low-risk option.

Richard
Click to expand...

I was almost tempted to agree with that Richard. But, it might also depend on which battery has been used for starting and how the batteries have all been kept charged. Assuming they have been kept reasonably well charged, the engine battery could be the better of the three, even if it's not the newest one, due to being cycled less. So i'd bare that in mind when deciding which to keep.
 
I would test the batteries on a lower current. Fully charge them, then disconnect the negative cables and let them rest for an hour. Record the voltages of all batteries. Connect a load of known current draw, such as a headlamp bulb, as mentioned. Leave for one hour. Disconnect the bulbs, wait a few minutes, and measure/record the voltages.

Repeat until the voltage of a battery reaches 12.2v, stop testing that battery, keep testing the others. 12.2v is 50% discharged, so i would not go lower than that. If you multiply the current draw of the bulbs used, in amps, by the hours it took to get to 12.2v you have the usable ah available from each battery.

For instance, a 55w headlamp bulb, at 12v, draws 4.58 amps. If it took 6 hours to get to 12.2v, then the usable ah of that battery is 27.8ah. Don't expect that with 10 year old batteries though :)
 
I did something like that a few years ago. Fully charged the battery then connected a car spotlamp (about 60W = 5A) and recorded the voltage every hour until it dropped to 12V

Gives you a pretty good way to assess the useful charge it is holding.

In my case this was prior to trying a magic battery reconditioner - it didn't work :(
 
PaulRainbow said:
I was almost tempted to agree with that Richard. But, it might also depend on which battery has been used for starting and how the batteries have all been kept charged. Assuming they have been kept reasonably well charged, the engine battery could be the better of the three, even if it's not the newest one, due to being cycled less. So i'd bare that in mind when deciding which to keep.
Click to expand...

Yes, I agree . :)

Richard
 
Current set up is that the two "banks" of two and one battery, each have a switch. That way I can have bank 1 or bank 2 or both. There's no separation of house and engine start. Usual practice is to start engine on the single battery, then switch all on together for parallel charging. After engine shutdown, switch the engine start single battery off and run on the two. There's a wind turbine that charges the set of two batteries only. (unless I switch all on, when one would charge into the other until all the same)
I'll try the lamp idea over the winter. Might end up buying three new ones? Thanks for answers.
 
I'm just amazed that your battery management skills have allowed you to function in this modern day and age with what looks to me like 110Ah of domestic capacity and a 55Ah engine starter battery and for so long!

Donald
 
Also if you want to go a bit geeky the raspberry pi is the way to go :cool:

With an ADS1115 voltage sensor across the battery terminals and an INA219 piggy backed across the existing battery monitor shunt (assuming there is one) you can set it up with no coding required to store to a inflxdb database then view from there >

mCP65hw.png
 
Back in the old days we used a 12V clock from an old car, a few headlamp bulbs and a relay adjusted to cut out at 12.0V.
These days, I'd probably use an Arduino.

It depends what you want to do.
Mostly all people need is a rough check on capacity and to chack that none of the batteries in a bank are causing a problem.

Another useful test is to put a battery on float charge for a long time and check that the current drops away to an acceptable value.
I've go a few of these:
https://www.ebay.co.uk/itm/LED-Digi...023449?hash=item2391ec1499:g:GToAAOSwBLlVF4PS
Each in its own plastic box with in &out terminals
Very useful for a simple check on what chargers are doing, whether a battery needs significant current to keep it floating at 13.4V or whatever.
 
Aja said:
I'm just amazed that your battery management skills have allowed you to function in this modern day and age with what looks to me like 110Ah of domestic capacity and a 55Ah engine starter battery and for so long!

Donald
Click to expand...

Its a 45 year old boat with very modest electrical demands. All LED lighting (though only the past 5 years or so), a few instruments, AIS, VHF. The biggest consumer is the SSB radio and that only used to transmit with the engine running. The life of the batteries perhaps suggest that this setup is enough.
A potential modification this winter is a split charge system to always charge the engine battery first, but then I only remember one time of having the engine battery get down enough to be unable to start the engine, and then the other bank did the job.
 
PaulRainbow said:
I would test the batteries on a lower current. Fully charge them, then disconnect the negative cables and let them rest for an hour. Record the voltages of all batteries. Connect a load of known current draw, such as a headlamp bulb, as mentioned. Leave for one hour. Disconnect the bulbs, wait a few minutes, and measure/record the voltages.

Repeat until the voltage of a battery reaches 12.2v, stop testing that battery, keep testing the others. 12.2v is 50% discharged, so i would not go lower than that. If you multiply the current draw of the bulbs used, in amps, by the hours it took to get to 12.2v you have the usable ah available from each battery.

For instance, a 55w headlamp bulb, at 12v, draws 4.58 amps. If it took 6 hours to get to 12.2v, then the usable ah of that battery is 27.8ah. Don't expect that with 10 year old batteries though :)
Click to expand...

I might just do this on my battery.
I am curious as to how the result would compare with the claimed amp hours on the battery label?
If i used this method on a brand new battery should it give the amp hours claimed or do manufacturers claim capacity down to battery destroying voltages?
Thanks
 
John the kiwi said:
I might just do this on my battery.
I am curious as to how the result would compare with the claimed amp hours on the battery label?
If i used this method on a brand new battery should it give the amp hours claimed or do manufacturers claim capacity down to battery destroying voltages?
Thanks
Click to expand...

Should be reasonably close John.
 
John the kiwi said:
I might just do this on my battery.
I am curious as to how the result would compare with the claimed amp hours on the battery label?
If i used this method on a brand new battery should it give the amp hours claimed or do manufacturers claim capacity down to battery destroying voltages?
Thanks
Click to expand...

The more usual 20H capacity measures down to 10.5v under load voltage. Not a destroying voltage once in a long while though if you get the battery straight back to full charge. Using voltage as a SOC indicator isn't great, needs a long time standing to stabilize and unless you have a constant temperature bath at 80dF or whatever the standard is the voltage will differ as well. But at least you'll learn *something*.

Plus lead acids take a few cycles to get up to full capacity when brand new, well Trojans do anyway, likely the same for others.

Some good real world examples on this site, so much forum stuff is shooting from the hip with no data.

https://marinehowto.com/category/electrical/batteries/

https://www.youtube.com/watch?v=oJ8AfJsOhsM
 
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