Battery charging issue

[rezer]

Hello all,

We have an issue with a battery brand I have not heard of and can't find anywhere on the web. It is an UltraTech 12120 battery (12V, 12AH). I suspect it may be Chinese, but I'm not sure.

The problem is when the system runs off of battery power for 4 hours and AC voltage is reapplied to charge the battery from a power supply, there is an initial charge current of 5A.
The spec sheet states 3A max and it takes about 2 hours for it to decline to that level.
Why the high initial charge current? Are we dealing with a cheap battery perhaps? Does anyone have any experience with this brand of battery?

Thank you for lending your expertise.

 

[Andrew Leigh]

Hi,

I assume this is a gel cell and not a lead acid?

Gel Cells are easily damaged by applying too much charging current and one should not exceed the manufacturers recommendations. Your charger should ideally be current limited to 3A.

A typical charge cycle will see the battery drawing as much current as ohms law will allow based on internal resistance and voltage. Yours is drawing 5A because the charger will deliver that current.

In your case, with a fully flat battery the charge cycle should begin at 3A. The current will slowly drop as the internal resistance and voltage changes, I would anticipate that the charging current should rereduce until the battery will "float" at about 200mA.

If your battery is still drawing in excess of 500mA it is still not charged.

I would suggest that your charger is not suitable for the battery in question.

Cheers
Andrew

 

[rezer]

I am not completely sure, but I believe it is a lead-acid battery since this is what we use most often. It's just a different brand that I am not familiar with. I will post a picture when I have access to my other computer. I may be able to make out the type. Thanks for your reply.

 

[ericgibbs]

I am not completely sure, but I believe it is a lead-acid battery since this is what we use most often. It's just a different brand that I am not familiar with. I will post a picture when I have access to my other computer. I may be able to make out the type. Thanks for your reply.

hi,
As Andrew says, it appears the charger isnt suited to that battery.

A quick solution you could try is to connect a power diode in series between the charger positive output and the battery positive.
A 5Amp diode should be OK, this will have the effect of reducing the charge voltage at the battery by about 0.7V or so.
If you find that the volts drop is too great, try schottky diode with say a 0.4V drop

 

[rezer]

hi,
As Andrew says, it appears the charger isnt suited to that battery.

A quick solution you could try is to connect a power diode in series between the charger positive output and the battery positive.
A 5Amp diode should be OK, this will have the effect of reducing the charge voltage at the battery by about 0.7V or so.
If you find that the volts drop is too great, try schottky diode with say a 0.4V drop

Since I haven't been able to get the spec sheet, the initial charge of 5A may be within specs. The 7AH is rated at 3A.
This is a lead-acid battery.

Eric,
If, after talking to my contact, the charging current is outside the spec, I will give your suggestion a try.

Thanks for your response.

 

[rezer]

Well, I think I found a solution. It appears you guys were dead on. We had them try a 3A power supply and the initial charge current was only 2.4A as opposed to 5A with a 6A supply. We still can't duplicate the issue here but it appears like a viable solution.

My thanks to Eric and Andrew for their input.

 

[crutschow]

I assume this is a gel cell and not a lead acid?

Just being picky, but to clarify, a gell cell is a type of lead acid battery, it's just that the acid is in a gell form.

 

[Andrew Leigh]

Not picky at all, I agree completely.

The reason for making the distinction was that "gel cells" are a little more fussy with the heat they can absorb hence the current limiting whilst "lead acids" are a little less so being vented.

What I should have asked was if the battery was sealed or not, that would have been more correct.

Cheers
Andrew

 

[Andrew Leigh]

Well, I think I found a solution. It appears you guys were dead on. We had them try a 3A power supply and the initial charge current was only 2.4A as opposed to 5A with a 6A supply. We still can't duplicate the issue here but it appears like a viable solution.

My thanks to Eric and Andrew for their input.

Here is a nice schematic from a trusted source for the identical charger you require. The charger will charge at 3A until it reaches 14.1V, at this point it reduces the charging to a safer level (slower rate) of 13,6V until full charge is reached.

**broken link removed**

Cheers
Andrew

 

[rezer]

Here is a nice schematic from a trusted source for the identical charger you require. The charger will charge at 3A until it reaches 14.1V, at this point it reduces the charging to a safer level (slower rate) of 13,6V until full charge is reached.

**broken link removed**

Cheers
Andrew

Thanks for the help. I had another thought of using a 3A polyfuse in line with the battery which should do the same thing.