0
\$\begingroup\$

I bought an ExpertPower EXP-1270 12v 7Ah battery, and I want to know how to charge it. I don't have a battery charger, but I want to do it with my variable power supply. I had already set it to 13.8v, but after charging for an hour or two the battery had only reached 13.2v. Am I doing something wrong?

I want to use the battery for general purpose where I can charge it, disconnect, and then use it for whatever I need to. When I'm done using it, I will recharge it again.

The battery has several specifications, including two voltages:

  • Standby voltage 13.7-13.9v

  • Cycle voltage 14.6-14.8v

  • Current limit 2.1A

  • Constant Voltage Charge

  • 12v 7Ah

  • 20HR

How should I charge it? I'm used to charging lithium batteries that don't take long to charge.

I'm just looking for what voltage and current I should use, and how long to charge for.

\$\endgroup\$
10
  • \$\begingroup\$ You need to tap into each cell voltage to find out if it damaged by unequal cell voltage. \$\endgroup\$
    – D.A.S.
    Commented May 21, 2021 at 12:47
  • \$\begingroup\$ These are brand new batteries so I don't think that would be the problem. This is a sealed AGM battery so I can't easily access the individual cells anyway \$\endgroup\$
    – Proxy303
    Commented May 21, 2021 at 12:47
  • \$\begingroup\$ Then use CC 2.1A and compute dV/dt when <14.6 which must be a temperature compensated voltage C=IcdV/dt what is C? A needle probe would have to be used carefully. If you can’t do it right , don’t \$\endgroup\$
    – D.A.S.
    Commented May 21, 2021 at 12:49
  • \$\begingroup\$ I'm still relatively new to electronics so I don't know all of this math stuff. Could you please explain? \$\endgroup\$
    – Proxy303
    Commented May 21, 2021 at 12:51
  • 1
    \$\begingroup\$ Just charge the battery with 13.8V with a 2.1A current limit at room temperature. It will be fine unless it's already damaged. In the future, invest in a good 3- or more stage battery charger. \$\endgroup\$
    – StarCat
    Commented May 21, 2021 at 14:57

2 Answers 2

Reset to default
1
\$\begingroup\$

So, the issue turned out to be that I had only left the battery charging for about an hour. Over a few more hours, the battery voltage has increased, so it is charging, its just being really slow about it. About an hour after I started charging it it had a voltage of 13.2v. Now it has a voltage of 13.6, about 3 hours later.

\$\endgroup\$
1
  • 1
    \$\begingroup\$ Based on the spec sheet you're looking at between 5 and 12 hours charging time depending on the charge current you limit to. \$\endgroup\$
    – Tom Carpenter
    Commented May 21, 2021 at 20:08
0
\$\begingroup\$

This 28 page technical manual describes concerns when charging or discharging sealed lead acid batteries:

https://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf

When a battery is charging at constant current the voltage tends to rise initially but then will become relatively constant while the battery absorbs more charge and then the voltage will rise again near the end of charging. However you are charging from a regulated voltage source, not a constant current source, so the voltage source has internal resistance and the battery has internal resistance which varies with the State of Charge, internal temperature, etc. The internal resistance forms a voltage divider with a voltage drop, compared to the no-load voltage of the charge source, based on the respective values of internal resistance. So it is not clear how you would determine end of charge or 100% capacity in your charging setup without some sort of smart charge integrated circuit or commercial charger.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.