Power supply as battery charger.

Submitted: Tuesday, Apr 18, 2006 at 11:45
ThreadID: 32986 Views:2644 Replies:9 FollowUps:9
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Hope a techo can help me. I purchased a 40 amp power supply to charge batteries now the same guy that sold it tells me he wouldn't use it as a battery charger. Different to what was discussed previously.

So, can I use a switch mode power supply to charge a bank of vehicle batteries???
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Reply By: Notso - Tuesday, Apr 18, 2006 at 11:56

Tuesday, Apr 18, 2006 at 11:56
Two problems as I see it,

First problem if you leave it connected too long it will cook the batteries

Second problem depending on the size of the battery bank you may overload the power supply and blow a fuze or it may shut off on overload.

So to use it you would need some sort of regulator between it and the batteries.

AnswerID: 167542

Follow Up By: hl - Tuesday, Apr 18, 2006 at 12:00

Tuesday, Apr 18, 2006 at 12:00
If it's output is 13.8V, you will not cook the batteries, in fact, you won't fully charge them either, but close enough.
It probably has current limiting and overload protection, so I can't see a real problem
If the voltage is adjustable, setting it to 14.2-14.4 should allow a full charge.
Cheers
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FollowupID: 422734

Follow Up By: Austravel - Tuesday, Apr 18, 2006 at 15:05

Tuesday, Apr 18, 2006 at 15:05
Hi,

It's a 3-15 Vdc 40 amp switch mode power supply so I can vary the volts to suit. Overload protection is via foldback circuitry (what ever that is).
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FollowupID: 422777

Follow Up By: Austravel - Tuesday, Apr 18, 2006 at 15:09

Tuesday, Apr 18, 2006 at 15:09
One more thing. When hooking up the leads I get a spark, is there a procedure to use for a power supply to make sure I don't damage it using it this way? Ie, have power supply turned on to roughly battery voltage before connecting to batteries etc.
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Follow Up By: hl - Tuesday, Apr 18, 2006 at 15:23

Tuesday, Apr 18, 2006 at 15:23
Hi again,

Just check the voltage output with a digi meter to ensure it is not more than 15V. If it is 15 or just under, I guess you can just connect it with the control wound up fully.
The spark is caused by the output capacitor charging, I would not connect or disconnect after the battery has been fully charged if it is a vented battery as it could send it into orbit (the battery and possibly you).
Foldback means it will limit the current to it's maximum rating by reducing (folding back) the voltage to achieve that.
I use an old switch mode supply that came out of a stadium lighting system. I have it set for 14.5 volts and it pumps 45 amps into my battery. Great if you want to bring it up to a reasonable state of charge in a hurry. Also great to use on the 240AC output of a cheap gennie. When the battery gets resonably full, it totally confuses the governor in the genni and it starts hunting. Interesting effect.

Cheers
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FollowupID: 422784

Follow Up By: Austravel - Wednesday, Apr 19, 2006 at 15:02

Wednesday, Apr 19, 2006 at 15:02
Thanks.
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FollowupID: 423018

Reply By: Notso - Tuesday, Apr 18, 2006 at 13:45

Tuesday, Apr 18, 2006 at 13:45
In my experience many power supplies are not effectively limited to the 13.8 volts at low current draw, so I still reckon the power supply is not a good option for battery charging without some sort of regulator.

Similarly if the batteries draw more than the 40amps when discharged it will probably blow a fuse or throw out the overload protection.
AnswerID: 167559

Follow Up By: Austravel - Tuesday, Apr 18, 2006 at 15:06

Tuesday, Apr 18, 2006 at 15:06
By a regulator do you mean voltage regulation?
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Reply By: Robin - Tuesday, Apr 18, 2006 at 14:31

Tuesday, Apr 18, 2006 at 14:31
Horses for Courses I guess - designing a professional solar system here right now with high quality IUOU characteristic automatic charger but use an old 7amp switchmode set to 14.2v as suggested by Hl at home myself to keep car batteries going. Overcharging is potential issue but at 14.2 and usually only keep it on for a few hours and all is ok.

My switchmode currents limits so don't usually blow any fuses

Robin Miller
AnswerID: 167571

Follow Up By: Austravel - Tuesday, Apr 18, 2006 at 15:07

Tuesday, Apr 18, 2006 at 15:07
The calcuim batteries I use have a max charge of 14.8 and the power supply is 15 so not really a drama.
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Reply By: Member - Phil G (SA) - Tuesday, Apr 18, 2006 at 15:49

Tuesday, Apr 18, 2006 at 15:49
I used a 25amp Jaycar 3-15volt power supply for a long time - just set the regulated voltage at 13.8 to 14.2 and leave it connected as long as you like - can't overcharge. Worked well.

My son moved out recently and flogged the power supply :-(( so I bought a switchmode 20amp power supply, and like you, I had a spark first time i hooked it up. So I've made up a charging lead with a 30amp switch in line. It is switched off when I hook it up to prevent the spark. I then turn on the power supply and turn the switch on, and it works fine. I don't like sparks near batteries :-(

I haven't had the switchmode supply very long, so still getting the feel of it. It regulates at 13.9 volts, so I anticipate it will do a good job of charging lead acid batteries.
AnswerID: 167579

Follow Up By: Austravel - Wednesday, Apr 19, 2006 at 15:03

Wednesday, Apr 19, 2006 at 15:03
Thanks Phil
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Reply By: Mike Harding - Tuesday, Apr 18, 2006 at 19:24

Tuesday, Apr 18, 2006 at 19:24
More specific please; what is "a bank of vehicle batteries".

The probable answer is; yes but don't set your charging voltage too high.

13V6 or so - is float charge and you can leave them forever like that.

14V2 or so - is a charging voltage and will force current into most batteries so you need to be aware of their state of charge and their ability to dissipate the excess energy - best not to leave them at that level for long after they reach full charge.

15V - will force even more charge into them - don't use it for too long although it may help to equalise the cells.

40A into a single battery is one hell of a lot of current and most batteries (including AGM - corrections?) won't accept that much (for long) due to their inherent internal impedance but it does give you the capability to abuse batteries and charging a "bank" of batteries in parallel does not guarantee that each of (say) four batteries will receive one quarter of the charge capability - one battery may grab 80% and the other three will share the remaining 20%, at least for some time - depends on many factors.

Collyn Rivers probably knows more about this than me if he chooses to comment?

Mike Harding
AnswerID: 167635

Follow Up By: Austravel - Wednesday, Apr 19, 2006 at 15:06

Wednesday, Apr 19, 2006 at 15:06
Thanks
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FollowupID: 423020

Reply By: Derek from Affordable Batteries & Radiators - Tuesday, Apr 18, 2006 at 19:39

Tuesday, Apr 18, 2006 at 19:39
I agree with Mike here. We need more info on the batteries. I would prefer to be using a 3 or 4 stage Smart Charger and be able to switch it on and forget about it.

People tend to forget things on and if you have $600 worth of batteries damaged you may wish you had an auto job.

The other option is to fit a timer and adjust voltage to suit but again this leaves a gap for human error.

Regards Derek.
AnswerID: 167642

Reply By: Geoff M (Newcastle, NSW) - Tuesday, Apr 18, 2006 at 21:13

Tuesday, Apr 18, 2006 at 21:13
Hi Austravel,
Derek and Mike are on the money with direct connection.

Another thought, KMart sell a gizmo in their battery/charger section the brand of which totally escapes me that if it could handle the current would turn any charger and I see no reason why it wouldn't work with a power supply into a 2 or 3 stage charger. Maybe someone else can fill in my memory gaps.

Or what should be the Rolls Royce solution,
http://www.sterling-power.com/pdf/bbc121245e.pdf
Just replace the battery input with your power supply and life should be grand.

Geoff.
Geoff,
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AnswerID: 167664

Reply By: Member - Mike DID - Tuesday, Apr 18, 2006 at 22:03

Tuesday, Apr 18, 2006 at 22:03
Also how quickly do you need to recharge the batteries ?

If it is just to keep them charged up, the just set the output to the batteries Float Voltage (13.6 to 13.8). They will charge slowly and never over-charge

Some switchmode Power Supplies will not work when connected to a battery - you may nee dto connect a high-current Diode between Battery and Supply.

Mike
AnswerID: 167680

Reply By: Austravel - Wednesday, Apr 19, 2006 at 15:07

Wednesday, Apr 19, 2006 at 15:07
Thanks all.
AnswerID: 167807

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