12v SLA Battery keeps charging over 15v?

[Saltda]

I picked up a couple of second hand electric razor scooters with charging issues. The batteries would only charge for a few minutes then the fully charged light would come on the charger. I figured the batteries in the scooter ( 2 x 12v SLA) were needing replaced.

I replaced the 2 batteries in one of the scooters at the weekend with 2 new batteries, these new batteries are taking a charge, but one of them always charges at over 15v regardless of the terminals its connected to. I tried another new battery to see if one of the new batteries was faulty, but the same thing happens, one battery is always over charging.

Are both the chargers faulty? The output voltage on both chargers is just over 13v when its not attached to the scooter.

Cheers

 

[ericmark]

There are many types of battery charger, the most basic is simply a transformer and rectifier and because the battery acts as a capacitor it will show a higher voltage when the battery is connected. These have no regulation and are not normally used for valve regulated lead acid (VRLA) batteries, these are used with batteries where you can top up the cells, however there are some cheap ones found in stair lifts, intruder alarms, and like where the manufacturer thinks he can get away with it.

The next level is a simple voltage regulator often fixed at 13.8 which is a little high but not too high.

The next is the stage charger which will charge a discharged battery at around 14.8 volt but measures the current, as the current drops which will vary according to the size of battery, it will switch from 14.8 volt to around 13.2 volt around 85% charged and slowly charge for last bit.

There are also pulse chargers which send a pulse to battery and measure how the voltage falls after each pulse and so change size of pulse, used in the main where the battery is being used while on charge, solar panels and the like.

I would guess you have a stage charger and you have measured in the so called second stage which is a constant high voltage around 14.8 volt and if you continue to charge when the battery reaches around 90% charge the volts will drop to around 13.4 volt, but you also could have a very cheap charger. Scooters I have seen up to now use switch mode stage chargers, but that does not mean they all do.

 

[EFLImpudence]

I picked up a couple of second hand electric razor scooters with charging issues. The batteries would only charge for a few minutes then the fully charged light would come on the charger.

Were they then fully charged?

I figured the batteries in the scooter ( 2 x 12v SLA) were needing replaced.

Why did you 'figure' that? Would they not start the engine?

I replaced the 2 batteries in one of the scooters at the weekend with 2 new batteries, these new batteries are taking a charge, but one of them always charges at over 15v regardless of the terminals its connected to. I tried another new battery to see if one of the new batteries was faulty, but the same thing happens, one battery is always over charging.
Are both the chargers faulty? The output voltage on both chargers is just over 13v when its not attached to the scooter.

I'm not sure what you mean by regardless of the terminals its connected to.
You must not connect them the wrong way round.


I do not know anything about the product but have found this -

http://support.razor.com/link/porta...is-the-recommended-battery-charging-procedure

 

[Saltda]

Were they then fully charged?


Why did you 'figure' that? Would they not start the engine?


I'm not sure what you mean by regardless of the terminals its connected to.
You must not connect them the wrong way round.


I do not know anything about the product but have found this -

View attachment 126568
http://support.razor.com/link/porta...is-the-recommended-battery-charging-procedure

No the original batteries were not holding a charge.

The terminals are the correct way round, I mean the position of the battery when seated in the scooter.

I have the original 24v chargers that came with the scooters when bought new.

Basically one battery is charging at over 15v, this will damage the battery, so cant keep charger connected to find out what it does at 80% charged.

 

[EFLImpudence]

Basically one battery is charging at over 15v, this will damage the battery, so cant keep charger connected to find out what it does at 80% charged.

That is normal.

First Q&A
https://www.powerstream.com/car-battery-faq.htm

 

[Saltda]

That is normal.

First Q&A
https://www.powerstream.com/car-battery-faq.htm

The battery is constantly being charged at 15.5v, this is not normal. It is being overcharged which is not good for the life of the battery and can be dangerous. Please note this is not a car battery nor a car's charging system.

I'm trying to find the reason why it is being overcharged, as the batteries are new and the chargers output voltages seem to be fine.

 

[bernardgreen]

Are you charging the batteries in the scooter or out of the scooter. ?

If you have a 24 volt charger and two 12 volt batteries then the batteries must be connected in series to make a 24 volt battery.


Chareger (+) --------- (+) battery 1 (-) ----------(+) battery 2 (-)--------(-) Charger


The two batteries should be the same type, make and age to ensure they get equally charged,

Connecting a single 12 volt battery to a 24 volt charger is very likely to damage the battery, the charger will never show "charged" as the charger is looking for nore than 26 volts from a 24 volt battery ( or pari of 12 volt batteries in series )

 

[EFLImpudence]

Please note this is not a car battery nor a car's charging system.

I thought you had removed the batteries and were charging them individually.

I'm trying to find the reason why it is being overcharged, as the batteries are new and the chargers output voltages seem to be fine.

Overcharging means continuing to charge after the battery is fully charged.

 

[Saltda]

The batteries are charging in the scooter. Both batteries are the same make, type etc. The charger is 24v.

 

[JohnW2]

The battery is constantly being charged at 15.5v, ... the chargers output voltages seem to be fine.

What are these "fine" output voltages of the charger and what is the 15.5V?

Kind Regards, John

 

[ericmark]

Theory should be 14.4 volt with VRLA but my stair lift is more like 30 volt the pair so 15 volt each, batteries last about 2 years only, the more it is used longer they last because it is basic a trickle charger with no regulation. My mobility scooter uses a stage charger and batteries still working about 15 years old.

 

[JohnW2]

Theory should be 14.4 volt with VRLA but my stair lift is more like 30 volt the pair so 15 volt each, batteries last about 2 years only, the more it is used longer they last because it is basic a trickle charger with no regulation.

The thing I didn't really understand is that the OP was talking about 'the output voltages of the charger" (which he says are 'fine') and the 'voltage at which the batteries are being charged' (which he thinks is too high) as if they were different things.

Kind Regards, John

 

[ericmark]

The thing I didn't really understand is that the OP was talking about 'the output voltages of the charger" (which he says are 'fine') and the 'voltage at which the batteries are being charged' (which he thinks is too high) as if they were different things.

Kind Regards, John

I see, so you think a cell has failed giving an imbalance between the two batteries. That is really the only way the charger voltage can be fine and one of the batteries have too high of a voltage if they have been always used and charged as a pair.

 

[JohnW2]

I see, so you think a cell has failed giving an imbalance between the two batteries. That is really the only way the charger voltage can be fine and one of the batteries have too high of a voltage if they have been always used and charged as a pair.

I'm just confused. The OP said that they were two new (and presumably identical) batteries, so pretty unlikely that one had a failed cell. Mind you he has said that one of them is 'charging at 15.5V', but hasn't told us about the other one.

Kind Regards, John

 

[ericmark]

One assumes two new batteries would have been manufactured at approximately the same time. However this may not be the case, one may have been in stock much longer than the other so one may have sulphated plates? If one battery is faulty in any way then they may charge uneven.

With standard lead acid it is the fill date that matters, but VRLA are filled at factory so it would be easy for one to be manufactured one month earlier than the other which could be enough to cause a miss match.