SLA Batteries And How to Charge Them?

[zakmuh]

Hi Guys,

Hope you all are doing well. I need your help to understanding the basics of battery voltage and ampere relationship.

What it is, my nephew has this ride-on car and the charger is misplaced somewhere. It has 2Nos 6v 7Ah SLA batteries. I've got loads of spare chargers and I want your help to find the right one for charging it please. Sorry I've got loads of questions here, just to keep it safe to avoid a fire hazard.

7Ah = 7000mA

1. What charger, with output 6V and 500mA or 12v 500mA or 12v 1500mA or a 12v 7000mA?
2. What difference the above different amperes would make to charging time, in hours?
3. What role ampere plays when riding the car? Say, replacing the batteries with 12v 20Ah would make the car go faster or prolong the riding time or both?
4. Would using a 12v 80Ah car battery do any harm to motors?
5. What would burn the motor, increasing the voltage (12v to 24v) or ampere (7A to 20A)?
6. Out of curiosity, powering the car with 12V AC (with an AC adaptor with cord), what affect would it make?

Many thanks in advance.

[zakmuh]

Krikkit said:

Always match the voltage - charge it at 6V......

Amperes is a measure of how much current a battery can provide - the Ah is effectively a power rating.

You could fit a single or pair of car batteries, but you'd need to be careful wiring up a pair (in parallel, not series), and also watch out that they're sealed too - you wouldn't want him rolling the thing over and getting a battery acid shower.

Thanks for your reply Krikkit.

So you're saying that use a 6v charger. But the there are 2 x 6v batteries, which means it need 12v charging? I just want to understand the reason behind your saying.

If Ah is power rating, then 20Ah would give high power to the motor make the car go faster? Would this still keep the riding time same or reduce it?

Pairing up two car batteries make it 24v?

[zakmuh]

MatthewH5 said:

zakmuh said:

Thanks for your reply Krikkit.

So you're saying that use a 6v charger. But the there are 2 x 6v batteries, which means it need 12v charging? I just want to understand the reason behind your saying.

If Ah is power rating, then 20Ah would give high power to the motor make the car go faster? Would this still keep the riding time same or reduce it?

Pairing up two car batteries make it 24v?

It depends if the batteries are wired in series or parallel.

A pair of 6V 7Ah batteries can be used together in two different ways:
- 12V 7Ah (series)
- 6V 14Ah (parallel)

Increasing the amp hours (Ah) will increase the range. The motor power will not be affected.

Increasing the voltage will make the motor turn faster (and likely burn it out).

Thanks Matt!

The batteries are wired in series in the car. So it has a 12V motor.

To keep the motors safe and increase the run time, I can simply use a car battery which has 80Ah rating- run time will increase by 10 times.

When it comes to charging the car battery though, if I used a 12v 500mA (most of the chargers re...), it'd take like whole day to get fully charged?

Please correct me if I'm wrong.

Cheers

[zakmuh]

Thanks.

please could you advice on these battery and charger?

Battery link- https://www.batterymasters.co.uk/sealed-lead-acid-...

Charger link- https://www.batterymasters.co.uk/battery-chargers/...

I'm thinking of replacing the existing once with two of these ones (ignore the listed price) and do parallel wiring, giving it 12V 45Ah. This will extend riding time to around 90mins?

[zakmuh]

TooMany2cvs said:

Hungrymc said:

OP - you cannot use the entire nominal capacity of the battery, else you will bugger them in short order. To be safe, work on half of the nominal time - so if you've got 45Ah which you think should give you 90min, work on 45min of actual use.

Edited by TooMany2cvs on Tuesday 15th May 12:42

Thanks mate. When you say 'work on', you mean don't ride the car for full 90mins - stop at 45 mins, let it cool down then recharge it?

From that table, what is ' charge state'? 11.9 = 40, means use it for 40mins max?

[zakmuh]

No, it hasn't got a cut off circuit. I'd work until its fully drained.

Batteries are not charging. So its time to replace them. I tried connecting the car battery 12V 80Ah and it worked well, but I had to hold the battery with long wires- car would move very slow due to battery weight.

[zakmuh]

Yeah I'll get one fitted. Cheers

Not really, I tested it connecting a 500mm long wires, just about holding the battery right behind the car.

Just a quick one, I can charge a battery using the PC power supply unit, which has 12v 5A output. Would high amp rate charging cause any damages to the battery?

[zakmuh]

TooMany2cvs said:

zakmuh said:

Just a quick one, I can charge a battery using the PC power supply unit, which has 12v 5A output.

No, you want about 14.5v to actually charge it. Just get a proper battery charger.

I can actually connect yellow +12v and purple -3v from the PSU, which makes it 15V.


Yeah, I'm about to order a cut off circuit

[zakmuh]

Thanks a lot guys for your help and advice.