Charging car battery with power supply

[seagull369]

I wanted to use a power supply to charge an automotive or deep cycle lead-acid battery (lead-calcium and lead-antimony, I think). It seems a good charge voltage seems to be around 14.3 or so, but am not sure what how low I should make the amp value drop to consider it fully charged. I've heard the number depends on the capacity of the battery (some percentage, I believe), but I haven't found that much additional info to support this.

Any suggestions?

 

[toolenthusiast]

Can I ask why? I mean, this is a solved problem. You’re inventing the battery charger.

 

[mogandave]

Will it cycle off once the battery is charged?

 

[tak1313]

Can I ask why? I mean, this is a solved problem. You’re inventing the battery charger.

Agreed - unless the OP is attempting to develop a new gizmo, these days one would spend more money constructing a DIY charger than just picking up a decent on at Amazon or Walmart. These days even smart chargers that use complicated charging and monitoring algorithms are pretty cheap because the smarts come on one chip - a company just needs to add the high current/volt part of the circuit to complete and it's done.

OR the OP just wants to construct a DIY charger as a hobby/fun project, and doesn't just want a charger to charge a battery/batteries. If that's the case, just Googling "wet cell charging" or similar will give more information than anyone could possibly need. As he/she mentioned 14.3 volts, I am assuming it's for a wet cell battery (even though more complicated algorithms do go as high as 15+v for brief moments under certain circumstances). Gel, Agm, et al. uses different algorithms using constant current or constant voltage, different voltage ramps, etc.

 

[seagull369]

I haven't had good luck with automatic battery chargers, as many others would attest to, especially when battery voltage is low. Using a power supply should be no different than a manual battery charger.

So, pretend it's a manual battery charger with an ammeter on it. What number should the needle on the gauge be pointing when it's at full charge?

 

[minke]

I'd recommend reading https://batteryuniversity.com/article/bu-403-charging-lead-acid

 

[Sumboodie]

12.6 volts is full charge on a 12v battery. Charge around 13-14 volts.

 

[Outahere]

https://www.trojanbattery.com/pdf/U.S.%20Battery%20Charge%20Profile%20Full%20%2011-12-13.pdf

 

[Leaflessshadetree]

I have used "wall wart" type power supplies to charge (or partially charge) deep cycle batteries. The issue with low current power supplies is they take a long time to charge a battery. If I recall after charging on the power supply overnight my charger would top one off in about an hour. It normally took 3-4 hours on the charger alone.

 

[American Locomotive]

Is this a "dumb" power supply (like a normal 12v or whatever DC supply that might power some random toy) , or an adjustable regulated power supply with voltage and current limits?

You really need a regulated supply to charge batteries based on current, as normal power supplies will increase voltage as current goes down - making it difficult to see when the battery is actually charged.

 

[Captain Spaulding]

In spite of people believing the marketing nonsense about multi-stage chargers, a battery charger is very simply a fixed voltage DC power supply that monitors current and steps the voltage down when the current drops to 1A.

They do nothing else. Absorption, bulk and finishing modes just describe how a battery behaves when attached to a fixed voltage supply. The charger changes nothing about its output ever until the current drops to 1A

Typically charging voltage is 14.6V and the float voltage is around 13.4V.

 

[American Locomotive]

That is not true.

A proper battery lead acid battery charger will charge in a constant current mode with an upper voltage limit. As the battery absorbs more charge, the charger will gradually increase voltage to maintain the set charge current. When the voltage hits the preset limit, the charger switches into constant voltage mode (14.4v or so) and will hold this voltage. The battery will gradually absorb the final charge, and the charger will monitor current. When the current drops low enough, the charger will either end the charge, or switch to float/maintain mode (13.6v or so).

I have a proper "smart" programmable battery charger, and it behaves exactly as described. I can set it to 200ma, 1, 10a, anything in between, and it will maintain exactly that charge current until 14.4v is achieved, at which point it switches to constant voltage mode, then eventually turns off once the charge completes.

What you described is how a car alternator charges a car battery. An alternator will do everything it can to maintain 14.4v on the electrical system - even if that means ramming 70A into the battery. Charging a battery at high currents like that is very hard on them, which is one of the reasons automotive batteries tend to be short lived. Especially if you deeply discharge them often.

 

[Captain Spaulding]

As an engineer who spent 11 years working on battery testing and charging systems, I assure you it is 100% true. The concept that a charger operates in constant current mode is 100% nonsense. The current stays constant only because it is providing all of the power it can. Either by it’s maximum capability or by a limit setting. The fact is, and I’d gladly bet you $10,000 on this, a charger can neither increase nor decrease charge current to a battery without also changing the voltage. If you set a current limit, the charger still operates as a fixed voltage DC power supply. No smarts and no multiple stages.

You are a victim of the scam marketing from charger manufacturers when they advertise “smart”or “multi-stage” chargers. It is 100% ********. If you want to take me up on the bet, let me know so I can get my new lift ordered.

 

[vwpieces]

I have done it in a pinch... 14V and I doubt your PS will have more than 20A. It'll work.
Could also just jumper it to a running car till it gets enough juice to be accepted by a smart charger.
If you can't get the batt over 10-11V, research how to check the individual cells, if the batt actually has removable caps. If one cell is dead your SOL and its junk.
But I keep Dumb chargers around to top up a batt to where a smart one will accept it.

 

[pbon]

My power supply for automotive programming does up to 100A. I assume it is variable and keeps the voltage steady.

MST-80 Auto Voltage Regulator for BMW and Benz

1

mhhauto.com

 

[American Locomotive]

As an engineer who spent 11 years working on battery testing and charging systems, I assure you it is 100% true. The concept that a charger operates in constant current mode is 100% nonsense. The current stays constant only because it is providing all of the power it can. Either by it’s maximum capability or by a limit setting.

Yes, that is how constant-current power supplies work. They have a feedback loop that adjusts the output to maintain a fixed current. If the effective impedance goes up, the power supply will increase voltage to maintain the same current. It's no different than a bench/lab power supply with a current limit setting.

The fact is, and I’d gladly bet you $10,000 on this, a charger can neither increase nor decrease charge current to a battery without also changing the voltage.

...I never claimed otherwise. That is literally how constant-current power supplies work. They vary their output voltage to main a fixed current setting.

If you set a current limit, the charger still operates as a fixed voltage DC power supply. No smarts and no multiple stages.

I have a 0-50A, 0-20v bench power supply with adjustable current and voltage limits. If I set a 5A current limit, then set the output voltage to 14.4v, and hook it up to a depleted 12v car battery, the output voltage will immediately pull down to around 12v, and the power supply will sit at the 5A limit. As the battery gains charge, the power supply will gradually increase the voltage to maintain the same 5A limit up until 14.4v is achieved. At that point, the power supply will go into constant voltage mode and the charge current still start to go down.

You are a victim of the scam marketing from charger manufacturers when they advertise “smart”or “multi-stage” chargers. It is 100% ********. If you want to take me up on the bet, let me know so I can get my new lift ordered.

No, this is basic power supply operation and battery charging methods.

Literally all modern devices charge batteries using CC-CV charging (Constant Current - Constant Voltage) - be it lead acid or lithium.