Hi, I am currently assembling a 36V 10Ah SLA pack but do not yet have a dedicated SLA charger. I was wondering how successful/safe would using a standard 42V 2A EZEE Lithium charger would be? I was going to connect and measure current flow as the recommended max initial per12V batt, of 14.4-15V @ 3A, would suggest OK, but thought it wise to ask first just in case ....
Temporary SLA Charger
- Thread starter skoolrun
- Start date
Lead-Acid batteries are charged using a fixed-voltage charger which raises the cells to a pre-set voltage. Li-Ion chargers are also fixed-voltage, with the cell-balancing intelligence built into the battery pack.
Don't blame me if you blow yourself up, but In theory at least, as long as the voltages are all correct, a LiIon charger should be OK for a Lead-Acid pack.
For a 36V Lead-Acid pack, you want a charging voltage of no more than 43.5V (absolute max), and at that voltage, you want to pay careful attention not to leave it on the charger for hours after the charging has finished. For a relatively safe charge, keep the voltage below 42V and you should be fine.
If you've got a voltmeter, confirm for absolute 100% certain that the Eeze charger doesn't go above 42V and you should be fine.
N.B. Even though I may be correct, please do bear in mind that you're taking advice here from someone who has managed to make many many different batteries explode over the years - Just because something is technically correct doesn't necessarily mean it's a good idea to do it. Do not leave your charger unattended... expecially if it's the wrong charger for the batteries you're charging.
Don't blame me if you blow yourself up, but In theory at least, as long as the voltages are all correct, a LiIon charger should be OK for a Lead-Acid pack.
For a 36V Lead-Acid pack, you want a charging voltage of no more than 43.5V (absolute max), and at that voltage, you want to pay careful attention not to leave it on the charger for hours after the charging has finished. For a relatively safe charge, keep the voltage below 42V and you should be fine.
If you've got a voltmeter, confirm for absolute 100% certain that the Eeze charger doesn't go above 42V and you should be fine.
N.B. Even though I may be correct, please do bear in mind that you're taking advice here from someone who has managed to make many many different batteries explode over the years - Just because something is technically correct doesn't necessarily mean it's a good idea to do it. Do not leave your charger unattended... expecially if it's the wrong charger for the batteries you're charging.
SLA batteries....
As a bit of a self-styled 'expert' on the subject of SLAs (they're a large part of the business I'm in) there are a few things you need to watch and be aware of....
I'd say that Fecn's assessment of a maximum 43.5 volts is definitely the maximum you should be aiming for and then only with a 'smart' SLA charger. A 'smart' 36V SLA charger will detect when it gets to 43.5 volts and then go to a 'float' mode at about 37.5 volts or cut off completely, and the usual Li-Ion 42 volt charger won't do that as it relies on the Li-Ion BMS to control the charge at the end. You need to go to 43.5 volts because otherwise the last 10% of the charge on an SLA can take many hours if you're even a little under - 42 volts from a constant-voltage Li-Ion charger will result in a fairly low charging current towards the end, and it's important that you do fully charge an SLA - its life will be compromised if you don't.
We use smart chargers built in to fire alarm systems. The point of these is that one of the design requirements for a fire alarm system is that the SLA battery pack must recharge from flat to 90% of its capacity within 24 hours, and so they go for it in a constant current mode until about 14.5 volts per 12 volt battery (the batteries will be fully charged at that point), and then switch to a constant voltage mode to maintain a float charge. Typically that is around 13.5 volts per 12 volt battery. At that voltage the battery will only take a few milliamps of current as it is fully charged and it can sit there indefinitely. If you go above that 13.5 volt point the current which flows increases quite a bit, and that results in gas being produced within the fully charged battery. SLAs in general are designed to recombine the gas as it's generated but they can only do this if the charging current is kept low once the battery is fully charged. That's why you need to keep an eye on things if you use a 42 volt Li-Ion charger.
The second thing to be aware of is what happens when an SLA is first put on charge from flat. Unless the charger has effective built-in current limiting, an SLA will happily take many amps to begin with, and you can't be sure with a Li-Ion charger that it won't blow itself to bits trying to deliver 50-100 amps into a flat SLA pack. The manufacturer of a Li-Ion charger may rely on the battery's BMS to provide the current limiting when the battery is flat, and you can usually only find out the hard way!.
I hope that's all fairly clear, and that I haven't confused you even more! In general, it's wise to use a charger designed for the battery technology. It's easy to think that a 36 volt battery can be treated in the same way as any other 36 volt battery whatever the technology, but it's not so simple especially when charging them.
Rog.
As a bit of a self-styled 'expert' on the subject of SLAs (they're a large part of the business I'm in) there are a few things you need to watch and be aware of....
I'd say that Fecn's assessment of a maximum 43.5 volts is definitely the maximum you should be aiming for and then only with a 'smart' SLA charger. A 'smart' 36V SLA charger will detect when it gets to 43.5 volts and then go to a 'float' mode at about 37.5 volts or cut off completely, and the usual Li-Ion 42 volt charger won't do that as it relies on the Li-Ion BMS to control the charge at the end. You need to go to 43.5 volts because otherwise the last 10% of the charge on an SLA can take many hours if you're even a little under - 42 volts from a constant-voltage Li-Ion charger will result in a fairly low charging current towards the end, and it's important that you do fully charge an SLA - its life will be compromised if you don't.
We use smart chargers built in to fire alarm systems. The point of these is that one of the design requirements for a fire alarm system is that the SLA battery pack must recharge from flat to 90% of its capacity within 24 hours, and so they go for it in a constant current mode until about 14.5 volts per 12 volt battery (the batteries will be fully charged at that point), and then switch to a constant voltage mode to maintain a float charge. Typically that is around 13.5 volts per 12 volt battery. At that voltage the battery will only take a few milliamps of current as it is fully charged and it can sit there indefinitely. If you go above that 13.5 volt point the current which flows increases quite a bit, and that results in gas being produced within the fully charged battery. SLAs in general are designed to recombine the gas as it's generated but they can only do this if the charging current is kept low once the battery is fully charged. That's why you need to keep an eye on things if you use a 42 volt Li-Ion charger.
The second thing to be aware of is what happens when an SLA is first put on charge from flat. Unless the charger has effective built-in current limiting, an SLA will happily take many amps to begin with, and you can't be sure with a Li-Ion charger that it won't blow itself to bits trying to deliver 50-100 amps into a flat SLA pack. The manufacturer of a Li-Ion charger may rely on the battery's BMS to provide the current limiting when the battery is flat, and you can usually only find out the hard way!.
I hope that's all fairly clear, and that I haven't confused you even more! In general, it's wise to use a charger designed for the battery technology. It's easy to think that a 36 volt battery can be treated in the same way as any other 36 volt battery whatever the technology, but it's not so simple especially when charging them.
Rog.
no way should you use your Li-ion charger
you need a 2 amp or 1.5 amp SLA charger with maximum voltage output of 43.5 volts
I have been using a car charger recently and had no problems, i guess on the plus point they charge very quickly even on the slow setting.
Don't know what difference it will make in the long term, but they were only £60 for 4 anyway so long as they don't blow up when i am next to them it isn't too bad.
Don't know what difference it will make in the long term, but they were only £60 for 4 anyway so long as they don't blow up when i am next to them it isn't too bad.
Many thanks for the comprehensive information and comments on the subject. I guess that I am going to have to purchase the correct charger if only to ensure the life of the SLAs. Out of interest after a short test run with the battery, I did connect the lithium charger for about an hour which sat around 41.5V for the duration, no explosions or other excitement to report 
.
Any recommendations for sourcing a reasonable quality smart charger?
.Any recommendations for sourcing a reasonable quality smart charger?
Glad it was of help....
A modern car battery charger is a cheap cost-effective way to go, provided you get the type which is regulated. All except for the cheapest are.
In past times a car battery charger was pretty crude - basically a specially constructed transformer and a rectifier. The transformer was 'special' in that it would have been constructed to have poor regulation so that it would have an effective current limit when connected to a flat battery. Once the battery was charged you knew it was time to disconnect because the battery would gas freely. This wasn't really a problem with old-style batteries because you just topped them up with distilled water as appropriate.
When all new cars are fitted with alternators they include proper electronic regulation. This allowed the introduction of 'maintenance free' car batteries which didn't need topping up and were some sort of a half-way construction between the old 'wet' battery and a modern dryfit or SLA. That's why modern chargers are regulated too.
There's really only one snag of course - they're 12 volt and so you have to charge your 36 volt pack in three stages which is inconvenient. A 36 volt charger will carry a hefty premium in price because not too many of them are made. You could of course remove your 36 volt pack and connect the three batteries in parallel for charging from a 12 volt car battery charger. Doing this will also help to keep the batteries synchronized. I think you mentioned that you were looking for a temporary solution, and if I were in your position that's what I'd do.
Rog.
A modern car battery charger is a cheap cost-effective way to go, provided you get the type which is regulated. All except for the cheapest are.
In past times a car battery charger was pretty crude - basically a specially constructed transformer and a rectifier. The transformer was 'special' in that it would have been constructed to have poor regulation so that it would have an effective current limit when connected to a flat battery. Once the battery was charged you knew it was time to disconnect because the battery would gas freely. This wasn't really a problem with old-style batteries because you just topped them up with distilled water as appropriate.
When all new cars are fitted with alternators they include proper electronic regulation. This allowed the introduction of 'maintenance free' car batteries which didn't need topping up and were some sort of a half-way construction between the old 'wet' battery and a modern dryfit or SLA. That's why modern chargers are regulated too.
There's really only one snag of course - they're 12 volt and so you have to charge your 36 volt pack in three stages which is inconvenient. A 36 volt charger will carry a hefty premium in price because not too many of them are made. You could of course remove your 36 volt pack and connect the three batteries in parallel for charging from a 12 volt car battery charger. Doing this will also help to keep the batteries synchronized. I think you mentioned that you were looking for a temporary solution, and if I were in your position that's what I'd do.
Rog.
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