Battery charger

[zachtheterrible]

My friend's sister just gave him an electric scooter, but he doesn't have the charger for it. I took a look under the "hood" and found two 12V batteries in series for a total of a 24V battery. I'm guessing it's lead acid because it gives an acid warning righ ton the side of the battery. How do I charge that kind of battery?

 

[Someone Electro]

These baterys need the lest care.Just run a few amps backaward the batery at about 25V.We it will reach full charge it will have the same voltage as the charhger and the curent will stop flowing.Its that simple.

You need somting that puts out 25V at a few amps.

You are in luck becose these betarys are the simplest to charge.But also the heaviest of all betarys.

 

[zachtheterrible]

Hey thanks electro :lol:

When you say charge it backwards, you mean put + of the PSU to - on the battery right? And vica versa?

And when you say a few amps, do you mean like 3 or 4? I would imagine the higher amperage output= faster battery charging?

 

[williB]

Zach , to charge a battery , you gotta put the plus of your source to the plus of the battery..
minus to minus..
assuming that your source is of a higher voltage than your battery..
what about charging them seperatly ?

 

[Someone Electro]

By backwards i meant ro run the curnt in the - and out the + pole pf the batery.

+ to - and - to + wod discharge the batery and start charging it in a negative voltage this wod destroy the baterys

Lead acid betrys can take high amps.You cod probobly charge it whith over 10 A unles if a realy small batery.Car baterys can put out more than 100A in periods.

If you have an 24-25V PSU laying around trconecting it to the batery.It just has to be the right voltage.So wen the batery is full it will have a litle more then 24V and if your suply is a litle more than 24V.So there will be no voltage driference betwen the batery and PSU so the curent will automaticly stop flowing and thats how you know your batery is full.

Or you cod take your the baterys and charge them seperetly whith an car batery charger.

Do you have an 24-25V power suply ?

 

[Oznog]

A 24V power supply will not charge it!
Charging a 24v lead acid battery requires 27.6v to 29.4v.

The ideal charging procedure is a constant voltage- generally on the high side of that range- until the current drops below a given threshold. Then the charger goes into a "topping" charge of perhaps the last 30% of the capacity, usually this is done in constant current mode. Then the charger should go into float mode where it just provides a trickle to counter normal self-discharge.

Usually cheap consumer stuff like this doesn't follow any such algorithm. They have a transformer, rectifier, cap, and resistor. Or probably no resistor. It's crude.

When you do this kind of unregulated charging, you end up with 2 possibilities. One is the charge voltage and rate is high and when the battery finishes it will receive an inordinately high overcharge as time goes on which will over time decrease the battery's performance and life. So you should take it off after you reckon it's charged (voltage and current readings help a LOT in guessing) and not leave it like that for many hours. Or on the other side you may have lower voltage and charge rate, it may take a very long time to charge, 12, 24 hrs, but the overcharge rate after that is not so bad so leaving it on for days will not do much damage. That's what the mfgs usually shoot for.

When it doubt, go with the low charge rate. What do you have to do this with?

 

[zachtheterrible]

I have a 0-30V 5A power supply that I'm hoping to use. There are two small batteries. My minibike has a 12V single battery w/ a 1A charger, so I reckon I won't be using more than 5A on this.

I'll try 29 volts, and since I my PSU has an amp meter built in, this will be a great help.

Thanks everyone, I'm gonna give it a shot :lol:

 

[Someone Electro]

Dose it have curent limiting too?

Beocse they have an realy low internal reistance.So dont blow your PSU.

 

[lord loh.]

I was just wondering if Lead Acid Battries charge better with rippled voltages... ie. output of a half wave rectifier?

What causes battries to charge better when a rippled charging voltage is applied ? (Assuming I am right that rippled voltages charge battries more efficiently :? )

 

[danielsmusic]

i found that too, i have a battery charger that "smokes" ni-cad's but with pulsing dc. why? it charges them from a car battery.

 

[zachtheterrible]

Hey electro, yes my PSU has current limiting.

Lord loh, I'm glad you bring that up. I was looking at the output of a 12v battery charger on my scope and saw a half wave riding on the DC 12v.

 

[Glyph]

rippled voltages

The rippled voltages need to be carefully controller to benefit the battery, otherwise if the ripples are too high and too frequent your peak voltage might be higher than the battery's safe voltage and start reducing its life. So make sure the peak voltage of those ripples isn't going over the target voltage you want to charge at. better to charge slow then to damage that battery.


google "Desulfator" and you'll get info on how CONTROLLED pulses of high voltage and current can actualy help the battery and extend its life. A desulfator can be built for $20.

 

[Someone Electro]

It may be just an transformer whith an bridge rectifier.

 

[zachtheterrible]

Well I don't really want to get into buildng a desulfator glyph, since it's my friend's scooter (not mine :lol: ) and he just wants to be able to charge the battery. I've got other projects to work on other than that. I'm sure I'll use that in the future sometime though. Thanks :lol:

Well I'm just going to buy a 25V wallwart T-former and call it a day. It worked fine charging it w/ 25V on my PSU.

 

[Someone Electro]

You cod make it a mod by sticking the wallwart inside the scooter so he can charge it anyware there an mains plug is.And he will never lose it(Unles he the looses the scooter)☺

 

[zachtheterrible]

That's a really good idea electro, I like the way you think. Maybe I'll try that :lol:

 

[Someone Electro]

Yea.

hey the ASCII icons work!

☺ ☻ ♥ ♦ ♣

As you can see its text and not an image.

 

[danielsmusic]

۩ ۝ ۞ ♣ ♂ ♀ ● ♪ ♥ ⅛ ⅓ ữ

 

[danielsmusic]

anyway, will my 12v 1A supply charge a 12V 7.2Ah sealed lead acid battery?

 

[williB]

do they have the symbol for ohms , in there ..
omega?
ps howd you do dat??