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Old 8th Apr 2018, 7:26 pm   #1
Jolly 7
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Default Charging Sealed Lead Acid Accumulators (SLA's)

Amongst other things, I bought a 6 volt 12Ah sealed lead acid battery from Maplin, hopefully to use with one of my radios. Does anyone know if it's possible to charge it with a 12V car battery charger ?
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Old 8th Apr 2018, 7:32 pm   #2
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Default Re: Maplin stores

Quick answer to that is no. All sealed lead acid batteries have strict charging guidelines.

Do a search for 'Yuasu little red book of batteries'.
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Old 8th Apr 2018, 10:26 pm   #3
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Default Re: Maplin stores

This is what I use.

https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1
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Old 8th Apr 2018, 11:18 pm   #4
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Default Re: Maplin stores

It is possible to charge 6V batteries by using a 12V car bulb in series. The bulb wattage will determine the charging current and positively prevent charging at excessive current. Unless trickle charging, it would be advisable to monitor the battery voltage manually. I have been charging sub-12V batteries for years with a 1960's simple 12V car battery charger and a lamp board with selection of old car bulbs that can be connected in series according to the charging current required.

I know that new technology batteries can be sensitive to charging currents, but the Lead-Acid ones seem pretty robust as long as they are not over-charged for a prolonged period. My wife's electric bike uses 3 x 12V `12Ah lead-Acid batteries, and about 5 years ago the charger developed a fault and applied around 50V for an extended period. We only noticed all was not well because the battery box was warm. The housings of the batteries (Lucas) swelled, but did not leak, and although they were never the same again, they still have enough Ah capacity to operate an electric car tyre pump and a small 12V electric drill. Rather than leave on permanently as suggested in the manual, the charger is now plugged into a time switch that charges for three 2 hour periods in 24 hours.
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Old 9th Apr 2018, 1:06 am   #5
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Default Re: Maplin stores

I use a 317 regulator set to either 13.8 volts or 6.9 volts for SLA batteries.
On the input side I have fitted a sensor with an LED that goes out when the current has fallen low enough to indicate full charge.
I have also got a charger that only puts out 250ma at 13.8V that has a medical name on it. When acquired it was set to 110V with only one of the primaries wired. It took ages and ages to charge a 17AH SLA but it did get there in the end.
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Old 9th Apr 2018, 4:13 pm   #6
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Default Re: Maplin stores

A scrap house alarm panel will yield a float charger to keep a 12V SLA battery topped up, without damage, if you want to get one for a future use.
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Old 9th Apr 2018, 6:15 pm   #7
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Default Re: Maplin stores

Quote:
Originally Posted by Refugee View Post
I use a 317 regulator set to either 13.8 volts or 6.9 volts for SLA batteries.
On the input side I have fitted a sensor with an LED that goes out when the current has fallen low enough to indicate full charge.
I have also got a charger that only puts out 250ma at 13.8V that has a medical name on it. When acquired it was set to 110V with only one of the primaries wired. It took ages and ages to charge a 17AH SLA but it did get there in the end.
I think I may have an LM317T regulator in my parts box and many power adaptors. I will try to design my 6.9 V SLA charger based on this.
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Old 9th Apr 2018, 10:22 pm   #8
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Default Re: Maplin stores

I normally use an L200 regulator chip. It has on board current limiting as well as voltage regulation, which is ideal for SLA battery charging. They have been around for years but are very easy to use and reliable.
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Old 10th Apr 2018, 12:09 am   #9
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Default Re: Maplin stores

The 317 has fixed current limit but for the long run it goes down with heat sink size due to it having an internal thermistor.
They give a short boost and then drop as they warm up.
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Old 10th Apr 2018, 12:41 am   #10
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Default Re: Maplin stores

Quote:
Originally Posted by Jolly 7 View Post
Amongst other things, I bought a 6 volt 12Ah sealed lead acid battery from Maplin, hopefully to use with one of my radios. Does anyone know if it's possible to charge it with a 12V car battery charger ?
Check out your local Lidl, they recently did a deal on intelligent chargers for about £10. They may have some left.
Decent bits of kit for keeping the motorbike batteries alive over the winter.

Regards
Bill
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Old 10th Apr 2018, 8:39 am   #11
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Default Re: Maplin stores

The charging voltage for an SLA is temperature dependant. If you use a regulator using a 2.7V zener as its reference to charge the battery this has a matching temperature coefficient.

There is an IC specifically designed for charging SLAs, the TI UC3906. This monitors the charge current and battery voltage to look after the battery. It charges the battery in 3 phases by monitoring the battery voltage while charging with a constant current. Once the voltage has reached a specified value it changes to a voltage limited charge cycle and monitors the charge current. Once the current has dropped to virtually zero it switches to a trickle charge phase with a lower charge voltage.

There is an application note available which fully describes the process.

Keith
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Old 10th Apr 2018, 11:00 am   #12
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

The basic 3 state 12V SLA charge cycle is current limited (limit depends on size of battery, using a lower than permitted limit is OK) with 14.4V (@25C- this is the temperature dependent voltage), then 14.4V with current falling away as battery charge completes, then when current falls to threshold level (maybe 10% of current limit value) drop to 13.8V (also temperature dependent) for long term float standby (or just turn off the charger).

Batteries in long term non floating storage should be fully charged and given a periodic topping charge every six months or so. More frequently if the temperature is high.

SLAs like to be kept around 20C or thereabouts. In float standby use, every ten degree rise in operating temperature halves the expected life!

Don't leave one flat ever if you can avoid it- it doesn't take long for irreversible capacity loss to set in.

Second the UC3906 recommendation- used them for years at work on SLAs used for mains fail backup for emergency shutdown controllers.
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Old 10th Apr 2018, 1:29 pm   #13
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Default Re: Maplin stores

Quote:
Originally Posted by peakfour View Post
Quote:
Originally Posted by Jolly 7 View Post
Amongst other things, I bought a 6 volt 12Ah sealed lead acid battery from Maplin, hopefully to use with one of my radios. Does anyone know if it's possible to charge it with a 12V car battery charger ?
Check out your local Lidl, they recently did a deal on intelligent chargers for about £10. They may have some left.
Decent bits of kit for keeping the motorbike batteries alive over the winter.

Regards
Bill
Seconded.

I think mine cost £15. It has an automatic sense for 6V and 12V batteries and 3 charge settings. 800mA max for 6V and motorcycle batteries of 12Ah or less and 3.8A for larger car batteries and finally a programme for cold temperature charging with a 14.8v setting. Combined with sense modes for battery state and a desulphation pulse charge programme and maintenance mode.
It brought two Gel type motorbike batteries from the dead that my local bike dealer told me were dud when all they needed was charging at the correct Voltage so on that score alone it was worth the money!

Keep an eye out in Lidl and Aldi, these chargers are no worse than my old Optimate which couldn't charge a modern battery and a new optimate was going to be upwards of £40! Virtually every one of my family and friends has chucked their optimates in the trash after suffering battery charging issues on motorcycles up to batteries failing when connected during winter layup and on maintenance mode. i won't do that now, i rather give the battery a charge and check it every couple of weeks and a top up when not in use.


A.

http://www.lidl-service.com/cps/rde/...ULG%203.8%20B1

Last edited by Station X; 10th Apr 2018 at 1:56 pm. Reason: Link added.
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Old 10th Apr 2018, 1:38 pm   #14
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

The other trick would be to get 2 x 6V batteries of the same Ah and charge them in series on a 12v charger.
bear in mind the fully charged voltage of a lead acid cell can vary according to its construction. Some 12V batteries are fully charged at 13.8V, some require nearly 15V. A lot of modern Automotive batteries fall into this criterion.

A.
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Old 10th Apr 2018, 10:00 pm   #15
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

Important NEVER to exceed the AH/10 charging rate, so for this, 12AH, maximum is 1.2 amps. They BULGE, some quicker than others, but they all do it if overcharged.
Just use any old charger with a suitable bulb to limit the charge, and let it run for 12 to 14 hours from flat.
Les.
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Old 10th Apr 2018, 10:13 pm   #16
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

Interesting premise.

Yuasa NP2-12 (2AH 12V) quotes max charging current of 500mA which is up at AH/4.

(Used this size for years at work).

Is the AH/10 figure just a rule of thumb to use if the battery is likely to be forcibly overcharged by an unregulated charger, to avoid rapid damage? If the correct charging voltage is applied, the current will fall near zero anyway as the charge approaches 100%.
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Old 10th Apr 2018, 10:27 pm   #17
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

Les' premise is correct in respect to traditional lead acid motorbike batteries that can be damaged by too high a charging current.
It gets complicated because certain modern batteries can be charged at higher rates and also some do need a higher voltage to fully charge.
I think that is the reason why motorcycle specific chargers have current limiters to prevent the plates overheating and warping if charged at too high a rate over time.
This kind of baffles me when I think about the charging system on a bike, it's basically only voltage regulated and the only current limiting is probably what the alternator can deliver. Certainly checking the output of the bike alternator across the battery indicates the full whack from the regulator gets shoved across the battery. This varies from around 14.5V on the modern triumph to something between 12.5 and 13V on the indian made Royal enfield, again I reckon this is a reason why I need to use a charger at intervals to getthe Gel battery up to scratch again. The charging circuit is fine for trad wet batteries but not up to the extra volts for the newer types. This i will bear in mind if and when i need to replace that battery.
A bit Off topic in that its Automotive related but on topic I hope in respect of different rechargable batteries?

A.
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Old 10th Apr 2018, 10:34 pm   #18
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

Fair comment, but the thread's about SLAs, not trad wet cell batteries.
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Old 10th Apr 2018, 11:35 pm   #19
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

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Fair comment, but the thread's about SLAs, not trad wet cell batteries.
Unless there's some sort of other difference, the only difference I know of between Sealed lead Acid batteries and traditional ones is that they can't be topped up to compensate for any boil off. They are still wet cell technology inside. And indeed one reason why many people I know prefer to stick with the old fashioned technology is that with careful and regular maintenance, the non sealed batteries can last longer. My experience with sealed batteries is that one day they work and the next they are dead as the proverbial Norwegian parrot. probably because the last bit of electrolyte has found its way out through the vents, they don't always recombine the hydrogen and oxygen products of electrolysis. I am not certain of the technology with Gel batteries but I wouldn't be surprised if they don't dry out in time also.

A.
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Old 10th Apr 2018, 11:48 pm   #20
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Default Re: Charging Sealed Lead Acid Accumulators (SLA's)

They used to be referred to as "gel" cells- and I think that this is the key, as an overcharged battery with acid-gel electrolyte tends to form a fine-bubble and (more-or-less) fixed insulating foam around the plates, whereas a traditional wet-cell battery will merrily bubble away with free release of hydrogen and oxygen and thus simply a hazard to smokers, rather than itself. The manufacturers like to talk about "recombinants" in later gel-cells- but I suspect that these potions are only effective in very mild cases of overcharging and this is the main reason why (somewhat) more sophisticated chargers are required for gel over wet lead-acid batteries, stopping bulk charging promptly on sensing full charge.
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