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Old 19th Sep 2017, 12:05 am   #1
ben
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Default Alternative to 12V dry fit lead acid battery?

I have a portable cassette recorder of early 90s vintage which has a fitted 12v 2.2Ah lead acid battery. This struggles to maintain its 12v o/p or retain a charge. I could buy a new replacement as they are still made, but before replacing I was wondering if there was a lighter alternative such as a AA Lithium or NiMh pack, maybe a modified laptop battery?

I also use this unit only occasionally, so want to avoid a risk of damaging the new battery through discharge and non use. Those lead acid batteries were used in 1980s panasonic VHS camcorders and I still have nightmares about the troubles they gave us!

The problem may be that the cassette unit is designed to trickle charge the lead acid battery. I think 40mA is the cut off voltage,and I doubt using more modern cells would work properly without modification. Would welcome suggestions if anyone has tried this e.g. on the Uher and Nagra decks.
TIA
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Old 19th Sep 2017, 12:30 am   #2
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Default Re: alternative to 12v dry fit lead acid battery?

Ben,

Generally I have been disappointed with the performance of gel cell batteries, they don't do very well trickle charged. The typical gel 12V type used in most alarm systems treated this way appear to only last 12 to 18 months these days.

I was faced with a similar problem to yours, but in this case to power a Tek 222ps scope. So I manufactured a custom battery with rechargeable AA's to replace the gel type. If you scroll to the end of the article you can see how the housing was made with folding and gluing transformer grade cardboard:

http://www.worldphaco.com/uploads/US...CILLOSCOPE.pdf
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Old 19th Sep 2017, 1:02 am   #3
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Default Re: alternative to 12v dry fit lead acid battery?

(I could have mentioned in the post above that this battery with the nickel metal hydride AA's has now been running well on its trickle charge and has been perfectly fine for 4 years now, despite also having put cells in parallel, with the rules observed in the article)
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Old 19th Sep 2017, 4:10 am   #4
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Default Re: alternative to 12v dry fit lead acid battery?

I would be very doubtful about replacing a lead acid battery with a different type as the charging requirements are different.
A 12 volt lead acid needs charging at a constant voltage. A nimih battery needs charging at a low and constant current, or higher current charging with a cut off when done.

I also have been disappointed with the performance of small sealed acid batteries, the larger ones seem better IME.
Perhaps the technology does not scale down well ?
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Old 19th Sep 2017, 5:38 am   #5
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Default Re: alternative to 12v dry fit lead acid battery?

Quote:
Originally Posted by broadgage View Post
I would be very doubtful about replacing a lead acid battery with a different type as the charging requirements are different.
A 12 volt lead acid needs charging at a constant voltage. A nimih battery needs charging at a low and constant current, or higher current charging with a cut off when done.
Yes that is true, especially if one wants a rapid charge, the charging protocols are different and important.

However in many applications either the gel, nicad or nimh do just as well as each other if they are on a trickle or low charge rate, in fact the latter two do better than the gel. This explains why in the the nimh AA batteries have proven to be a great alternative to the gel cells in the scope application I cited.

Generally, many devices that use gel cells, run a fairly low charge rate anyway because the apparatus normally runs on mains power and the battery is floated for a backup. Often there is not a fast charge protocol there. This is why you can get away with substituting other types of rechargeable cells, without necessarily having to modify the charge circuits. But that can also be done if the charge rate is too aggressive/high.
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Old 19th Sep 2017, 8:54 am   #6
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Default Re: alternative to 12v dry fit lead acid battery?

NiMh cells can be float charged at 1/20 of their mA hour rate.
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Old 19th Sep 2017, 9:24 am   #7
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Default Re: Alternative to 12V dry fit lead acid battery?

I was once told that with lead acid gel batteries the small batteries are more problematic than the larger ones. With much experience of use of these in use in consumer's homes (similar arrangement to alarm systems) we did find this to be the case. 12V 7Ah batteries seemed to soldier on for years, but 2Ah were far more problematic. The much smaller 0.8Ah types were even worse.
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Old 19th Sep 2017, 11:00 am   #8
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Default Re: Alternative to 12V dry fit lead acid battery?

Cyclon Cells, lead acid chemistry and bullet proof.
 
Old 19th Sep 2017, 12:52 pm   #9
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Default Re: Alternative to 12V dry fit lead acid battery?

I'd agree with that.
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Old 19th Sep 2017, 12:57 pm   #10
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Default Re: Alternative to 12V dry fit lead acid battery?

A radical suggestion: what about a Lithium Iron Phosphate (LiFePO4) battery? Four cells give a very similar voltage to a six-cell lead-acid battery, similar enough that it's possible to use them as a direct replacement in a car electrical system. They're much smaller and lighter than lead-acid and (I know from experience in my day job) extremely robust against various types of abuse. Here's a possible candidate:

https://www.ev-power.eu/LiFeYPO4-bat...h-LiFePO4.html

I have no connection with the supplier other than as a satisfied customer.

Note that these are not the same cell chemistry as the Lithium batteries used in phones and laptops. LiFePO4 cells are not as compact as laptop-type cells, but are much more robust, and therefore much safer. The charging requirements are very uncomplicated, just don't let them get overcharged to more than about 3.8V per cell. When discharging, you're supposed to stop at 2.6V per cell (the exact values may vary depending on the cell manufacturer - check the data sheet) but we've had them discharge to zero volts and still recover fine.

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Old 19th Sep 2017, 1:44 pm   #11
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Default Re: Alternative to 12V dry fit lead acid battery?

I would second LiFePO.
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Old 19th Sep 2017, 2:09 pm   #12
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Default Re: Alternative to 12V dry fit lead acid battery?

I would too, one great advantage is the low self discharge rate of the LiFePO, somewhat akin to the lead acid in fact. But still, good old cheap nicads and nimh cells also do the trick if they are on trickle charge anyway as the self discharge becomes academic and they still appear to out perform the gel cell for life expectancy.
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Old 19th Sep 2017, 9:46 pm   #13
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Default Re: Alternative to 12V dry fit lead acid battery?

If considering lithium iron phosphate batteries for lead acid replacements, do be very careful that the replacement battery has sufficient capacity in true, measured AH.
Many suppliers of these batteries are quoting not true AH but "lead acid equivalent" AH. This is the suppliers estimate of the size of lead acid battery that can be replaced and give similar engine starting performance.

So a 17AH (PB equivalent) lithium iron phosphate battery may have actual capacity of perhaps 4AH but is claimed to have the same engine cranking performance as a 17AH lead acid battery. This may even be true, but try drawing one amp from the battery and see how long it lasts ! about 3 hours, rather than about 17 hours, I suspect !

These batteries seemed to be largely aimed at those who ride motorcycles competitively, the weight reduction is crucial in such cases, and the other criteria is "will it reliably start the engine" No one cares about for long the lights may be lit for without running the engine.
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Old 20th Sep 2017, 5:12 pm   #14
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Default Re: Alternative to 12V dry fit lead acid battery?

In the 1970's I remember reading in a SAFT catalogue that they did a special range of batteries designed for starting aircraft engines that, while having a relatively low Ah capacity, had a very low internal resistance to provide a high cranking current. One of our engineers had bought such a battery as unused government surplus stock and used it in his car to good effect. When taking it in for a service he did warn the garage not to test the battery by sticking a screwdriver across it as some older mechanics were wont to do at that time. This was ignored, with fatal consequences for the screwdriver.
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