Testing/checking maintenance free lead, sealed acid batteries

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mocruising

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When I used the standard type of screw cap lead acid batteries I used to check the cells individually monthly and keep a log with a hydrometer to keep an eye on decaying cells.

How does one know how sealed batteries are.
 
In my other life, I race electric powered cars with my students from my school, we use AGM sealed batteries and almost kill them every race... this is not my work, but a good way to find the bad battery.


The idea with this thing is that you wire it onto a full battery, press a button to start the discharge then walk away - it discharges at near the F24 rate until the battery goes down to 10.6V then it stops discharging and the timer tells you how long it's taken. You can go back to it a day later if you want. The battery is not damaged because the discharge stops with an on-load voltage of 10.6V (after switch off this will spring back up to 12.1V or so).
I found a suitable timer on ebay for about £7.50. it's called a "mini time accumulator" and you want the "volts free" one with display description "0-99h59m59s" e.g.
http://www.ebay.co.uk/sch/i.html?_n...counter&_osacat=0&_trksid=p3286.c0.m270.l1313
The circuit can be built on stripboard. Below I give the RS components stock numbers of some of the important parts:
relay (418 6170) cost £2.34
zener diode (10V) (812 465) cost 26p x5 or any 10V zener
diode (544 3480) cost 1.2px20 or any small signal diode e.g. 1N4148
transistor BC557 (545 2260) cost 10px5 or any small signal PNP
power resistors (252 2906) cost £3.95 - you need 2 of these, it's a 100W 1.5ohm resistor
You'll also need a pushbutton switch and a couple of small resistors at 100ohm and 220ohm.
Depending on your heatsink you will probably want a small 12V fan as well. you're pushing 200W into the heatsink, it's going to warm up ;^)
Oh yes - have you noticed you'll need a heatsink of some description...



OK here are some pictures: complete discharger module
http://i543.photobucket.com/albums/gg471/bobc0/greenpower/discharger.jpg
the control circuit on veroboard (stripboard)
http://i543.photobucket.com/albums/gg471/bobc0/greenpower/discont.jpg
and, most importantly, the circuit diagram
http://i543.photobucket.com/albums/gg471/bobc0/greenpower/dischsch.jpg

Enjoy, a bit ott for a boat though???
 
Alpha22

10 out of 10 for the quality of the reply!!!!

Perhaps there is a market for the gadget that you build, but most people either could not, or don't have the time to, build their own.
 
I'm impressed! As you say you can't observe the condition of individual cells with a sealed battery, which is a shame but it didn't stop the battery from failing. Luckily I have a friend who used to work for Lucas so he has a battery drop tester. The characteristics of the battery are set in the tester and it loads the battery for perhaps a minute (I can't remember) and gives performance figures for charge and capacity. I believe many of the older garages will still have one - though most now just sell you a new battery even if you didn't need one!

Rob.
 
mocruising said:
When I used the standard type of screw cap lead acid batteries I used to check the cells individually monthly and keep a log with a hydrometer to keep an eye on decaying cells.

How does one know how sealed batteries are.
Click to expand...

About all you can do is to use a digital voltmeter.

Charge the battery. and allow it to stand with no charge or load for 12 to 24 hours....... you decide the time interval and then always stick to it....... then ceck the volts

If it up to 12.7 ish or more then it has charged. If it is not then try some more charging and repeat the test.

If you cannot get to something around 12.7 ( 12.6 at least) then its days are numbered

having charged it to the best you can. ideally let it stand for sevral days or weeks and monitor the rate at which the volts fall. They will go down fairly quickly at first but then more slowly. A ggod battery with no load should take severl weeks before the volts have fallen down towards 12.5.

I take 12.7 as fully charged , 11.7 as effectively flat with a linear realionship in between ... so 12.2 is about half charged

useful graph from the old "Voltwatch" website (not quite matching my 12.7 and 11.7 figures but there are nearly as vary variations as there are websites on the subject)

wp834ca5fb.png



BTW I do have a hydrometer but seldom use it.
 
Last edited:
Alpha22 said:
In my other life, I race electric powered cars with my students from my school, we use AGM sealed batteries and almost kill them every race... this is not my work, but a good way to find the bad battery.


The idea with this thing is that you wire it onto a full battery, press a button to start the discharge then walk away - it discharges at near the F24 rate until the battery goes down to 10.6V then it stops discharging and the timer tells you how long it's taken. You can go back to it a day later if you want. The battery is not damaged because the discharge stops with an on-load voltage of 10.6V (after switch off this will spring back up to 12.1V or so).
I found a suitable timer on ebay for about £7.50. it's called a "mini time accumulator" and you want the "volts free" one with display description "0-99h59m59s" e.g.
http://www.ebay.co.uk/sch/i.html?_n...counter&_osacat=0&_trksid=p3286.c0.m270.l1313
The circuit can be built on stripboard. Below I give the RS components stock numbers of some of the important parts:
relay (418 6170) cost £2.34
zener diode (10V) (812 465) cost 26p x5 or any 10V zener
diode (544 3480) cost 1.2px20 or any small signal diode e.g. 1N4148
transistor BC557 (545 2260) cost 10px5 or any small signal PNP
power resistors (252 2906) cost £3.95 - you need 2 of these, it's a 100W 1.5ohm resistor
You'll also need a pushbutton switch and a couple of small resistors at 100ohm and 220ohm.
Depending on your heatsink you will probably want a small 12V fan as well. you're pushing 200W into the heatsink, it's going to warm up ;^)
Oh yes - have you noticed you'll need a heatsink of some description...

OK here are some pictures: complete discharger module
http://i543.photobucket.com/albums/gg471/bobc0/greenpower/discharger.jpg
the control circuit on veroboard (stripboard)
http://i543.photobucket.com/albums/gg471/bobc0/greenpower/discont.jpg
and, most importantly, the circuit diagram
http://i543.photobucket.com/albums/gg471/bobc0/greenpower/dischsch.jpg

Enjoy, a bit ott for a boat though???
Click to expand...
A capacity test is useful occasionaly on a battery when you want to know its status. You can do the same thing manually by just monitoring the voltage with a set load on.
These tests will shorten the life of a lead acid battery. The number of discharge cycles is limited. If you discharge the battery, even a good quality deep cycle battery a long way the number of cycles is small so don't do the test unnecessarily.
 
Conachair said:
How do you do that? Istr that capacity is non linear against discharge rate as too is voltage, how do you get a reliable c20 figure?
Click to expand...
The Ampnours out are easy to measure precisely with a battery monitor, but you can very close with few readings and a simple multimeter.
The discharge current will not stay exactly the same, as the voltage drops, but the battery monitor will take this into account. The capacity does not vary with slight changes in the discharge rate. C20 will not be very different to C25.
 
noelex said:
The Ampnours out are easy to measure precisely with a battery monitor, but you can very close with few readings and a simple multimeter.
The discharge current will not stay exactly the same, as the voltage drops, but the battery monitor will take this into account. The capacity does not vary with slight changes in the discharge rate. C20 will not be very different to C25.
Click to expand...

Nope, still don´t get it, how do you measure the amps going out of the battery?
 
Conachair said:
Nope, still don´t get it, how do you measure the amps going out of the battery?
Click to expand...

Amps can be measured with any multimeter, battery monitor, clamp on multimeter. If you desperate you can even use the wattage of things like an incandescent light globe, for a rough idea, but when multimeters can purchased for few pounds ( and every boat should have one) you would have to be desperate.
If you mean amp hours you need a battery monitor or any of the above instruments and a watch. 10A for 1 hour is 10 AHrs.
 
noelex said:
Amps can be measured with any multimeter, battery monitor, clamp on multimeter. If you desperate you can even use the wattage of things like an incandescent light globe, for a rough idea, but when multimeters can purchased for few pounds ( and every boat should have one) you would have to be desperate.
If you mean amp hours you need a battery monitor or any of the above instruments and a watch. 10A for 1 hour is 10 AHrs.
Click to expand...

Ah, just checked the previous post, missed the "set load" bit and thought you were doing something special just using voltage. :o

But basically the same thing but without the automation bit.
 
Nothing much to add to previous, except to say that you must remember to pull the plug and stop discharging when you reach the critical loaded voltage (10.6v from memory for a c10) for your battery. How you achieve that is down to either an auto system as suggested by Alpha22, or you keep a watchful eye on the voltage - hourly in the middle period, moving to half hourly, then quarter as you drop below say 12 volts.

In a previous employment, we did a full discharge test annually on radio station batteries - they lasted for decades - and it was good enough to pick up any bad cells before they became a liability.

And don't wait too long before recharging.
 
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