Trickle charging a 33Ah battery.

[Bas Horneman]

I got a 33Ah battery for the price of a 7,2Ah battery, for my DDDAC1543.

And I was thinking having made CCS with DN2540 that I could make a nice trickle charger with a 12V regulator followed by a CCS. Would that be enough...I realize it has nothing built in to stop charging once the battery is full.

But what current would constitute a good trickle charge current for such a battery?

Regards,
Bas

[Jaka Racman]

Hi,

http://focus.ti.com/lit/ds/symlink/uc3906.pdf and http://focus.ti.com/lit/an/slua115/slua115.pdf .

Best regards,

Jaka Racman

[Pjotr]

Hi Bas,

If it is a lead-acid battery you should charge with a current limited constant voltage. The voltage is then 2.25V/cell to 2.35V/cell, it is somewhat temperature dependent but 2.35V/cell is a good average. Current limiting is 0.1 to 0.3 the AH rating of the battery. When the battery is full it simply stops drawing current so you can leave the charger standby for trickle charging. If you choose 2.25V/cell you can leave it connected permanently.

The UC3906 is a good solution but difficult to get. You can make something similar yourself with a 5A LM317-like regulator. Initially charge at 2.35/cell and switch to 2.25V/cell trickle charging when the battery charging current falls below 1/50 - 1/100 the AH rating of the battery.

Cheers

[Bas Horneman]

Thanks Jaka...interesting reading...


Hallo Pjotr,

2.25V/cell

What is cell? In my case a 12volt battery?

= 0,1875 What does that mean?


0.1 * 33 = 3,3A max...

but for trickle I could just go say 100mA?

Cheers,
Bas

[Pjotr]

Hi Bas,

Although the battery is stated 12V its actual voltage is something between 12V and 13V. At 12V (unloaded) it is almost empty and at 11V it is fully empty. Don’t discharge below 11V, it will destroy the battery.

A lead-acid battery is usually made of more batteries of 2V in series to get the target voltage but the batteries are packed in one box. Each separate battery is then called a “cell”. A 6V battery contains 3 cells and a 12V battery contains 6 cells of 2V each.

So if you make a regulator of 6 x 2.25V = 13.5V you can use that for trickle charging. For recharging you need 6 x 2.35V = 14.1V. The simplest solution is to make something with an LM317 with switcheable output voltage and a current meter. For charging use the 14.1V and when the current falls below say 0.5A for your 33AH battery, switch it to 13.5V. If you use 13.5V for recharging it will take a very long time to recharge the battery.

Note: In contrast to Nicads always keep a lead-acid battery fully charged after each use. That way it will last longest. Leaving a lead-acid battery in discharged condition for prolonged time will shorten its lifetime severely.

Cheers

[Bas Horneman]

So if you make a regulator of 6 x 2.25V = 13.5V you can use that for trickle charging. For recharging you need 6 x 2.35V = 14.1V. The simplest solution is to make something with an LM317 with switcheable output voltage and a current meter. For charging use the 14.1V and when the current falls below say 0.5A for your 33AH battery, switch it to 13.5V. If you use 13.5V for recharging it will take a very long time to recharge the battery.

Thanks Pjotr!

I will just use an ordinary LM317 with the 2 modes you suggested. And just add a switch for the modes, with a litte current meter to check...so I know when to flick the switch.

Cheers,
Bas

[li_gangyi]

u could use a transistor to switch automatically...seen it done somewhere...