Pb Battery Recharge. - UK Vintage Radio Repair and Restoration Discussion Forum

erasmo0 · 23rd Dec 2020, 4:30 am

I am about to charge a lead acid battery with a stabilized power supply ... if accidentally the charge is interrupted by an external factor, can the 74 A / h of the battery cause damage to the stabilized power supply?

Radio Wrangler · 23rd Dec 2020, 8:50 am

Yes.

Some stabilised power supplies can survive this but many do not. I'm assuming it's a 12v battery, and that is enough voltage to avalanche the base-emitter junctions in the power transistors of typical regulated power supplies.

Also, the better qualith laboratory grade reulated power supplies may have 'down programming' facilities, so that if you turn down the voltage control, it will try to discharge any capacitors on its output to get to the voltage you set. These are not powerful to survive the currents from a large battery.

Either use a purpose-designed battery charger, or use a series diode between the power supply and the battery. Increase the supply voltage to allow for the diode drop. Use a diode big enough to handle the charging current.

Destroying lab power supplies by trying to use them to charge batteries is quite common.

David

erasmo0 · 24th Dec 2020, 4:55 am

“Destroying lab power supplies by trying to use them to charge batteries is quite common”...you made me think ... but when I charge the battery (pb) with a battery charger (pb) can I leave the positive pole and also the negative attached or do I have to disconnect one of the two?

Diabolical Artificer · 26th Dec 2020, 8:12 am

I have a shed full of damaged 12v supplies as a testament to the inadvisability of this practice, most were simple constant voltage types.

To charge a lead battery you need a current limited supply as the first part of the charging cycle should be set to a 1/4 of the battery's capacity, EG 10AH rated = 2.5A @ 14.6v. When current has fallen to 100mA, you switch to constant voltage @ 13.6v, after this you just set the PSU to trickle charge, more info attached.

Andy.

broadgage · 26th Dec 2020, 9:51 am

A minority of bench power supplies CAN be used as battery chargers, but most can not. Presume that yours should not be used as a battery charger.

Connect a suitably rated silicon power diode in series with the battery, remembering to increase the charging voltage by about 0.7 volt due to the voltage drop in this diode.

Or buy a purpose made battery charger. If your battery is a sealed type, make certain that a purchased battery charger is suitable for sealed batteries.

A 12 volt lead acid battery can be charged at a constant voltage of 13.7 to 13.8 volts, a full charge takes a couple of days. The size of the charger is not important with a constant voltage charger. A 50 amp charger can be used with say a 7 amp hour battery, it WILL NOT put 50 amps into the small battery, the battery only takes what it needs.
A small constant voltage battery charger with a 100ma output will fully charge a 75 amp hour battery, though it may take about a month.
Load current may be taken from a battery connected to a constant voltage charger provided that this is lessthan the charger output.

A quicker charge is possible at a higher voltage , but this must be limited in both initial current and in the time for which it is applied. "Smart" or "multi stage" battery chargers are available that do this.

Note that a multi stage battery charger MUST be of the correct size for the battery. A charger intended for a small battery may grossly over charge and destroy a large battery (rather counter intuitively)
No load should be taken from a battery connected to a multi stage charger or it may become "confused" and over charge the battery.
The mains supply into a multi stage charger should be reasonably reliable, frequent interuptions can over charge the battery.

23rd Dec 2020, 4:30 am	#1
erasmo0 Tetrode Join Date: Nov 2020 Location: Udine, Italy. Posts: 59	Pb Battery Recharge. I am about to charge a lead acid battery with a stabilized power supply ... if accidentally the charge is interrupted by an external factor, can the 74 A / h of the battery cause damage to the stabilized power supply?

23rd Dec 2020, 8:50 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,901	Re: Pn _ battere Recharge Yes. Some stabilised power supplies can survive this but many do not. I'm assuming it's a 12v battery, and that is enough voltage to avalanche the base-emitter junctions in the power transistors of typical regulated power supplies. Also, the better qualith laboratory grade reulated power supplies may have 'down programming' facilities, so that if you turn down the voltage control, it will try to discharge any capacitors on its output to get to the voltage you set. These are not powerful to survive the currents from a large battery. Either use a purpose-designed battery charger, or use a series diode between the power supply and the battery. Increase the supply voltage to allow for the diode drop. Use a diode big enough to handle the charging current. Destroying lab power supplies by trying to use them to charge batteries is quite common. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

24th Dec 2020, 4:55 am	#3
erasmo0 Tetrode Join Date: Nov 2020 Location: Udine, Italy. Posts: 59	Re: Pn _ battere Recharge “Destroying lab power supplies by trying to use them to charge batteries is quite common”...you made me think ... but when I charge the battery (pb) with a battery charger (pb) can I leave the positive pole and also the negative attached or do I have to disconnect one of the two?

26th Dec 2020, 9:51 am	#5
broadgage Nonode Join Date: Jan 2010 Location: North Somerset, UK. Posts: 2,130	Re: Pb Battery Recharge. A minority of bench power supplies CAN be used as battery chargers, but most can not. Presume that yours should not be used as a battery charger. Connect a suitably rated silicon power diode in series with the battery, remembering to increase the charging voltage by about 0.7 volt due to the voltage drop in this diode. Or buy a purpose made battery charger. If your battery is a sealed type, make certain that a purchased battery charger is suitable for sealed batteries. A 12 volt lead acid battery can be charged at a constant voltage of 13.7 to 13.8 volts, a full charge takes a couple of days. The size of the charger is not important with a constant voltage charger. A 50 amp charger can be used with say a 7 amp hour battery, it WILL NOT put 50 amps into the small battery, the battery only takes what it needs. A small constant voltage battery charger with a 100ma output will fully charge a 75 amp hour battery, though it may take about a month. Load current may be taken from a battery connected to a constant voltage charger provided that this is lessthan the charger output. A quicker charge is possible at a higher voltage , but this must be limited in both initial current and in the time for which it is applied. "Smart" or "multi stage" battery chargers are available that do this. Note that a multi stage battery charger MUST be of the correct size for the battery. A charger intended for a small battery may grossly over charge and destroy a large battery (rather counter intuitively) No load should be taken from a battery connected to a multi stage charger or it may become "confused" and over charge the battery. The mains supply into a multi stage charger should be reasonably reliable, frequent interuptions can over charge the battery.