I need to boost power supply voltage...

Anyone know how to adjust voltage on a power supply? I'm looking for 15 or more volts for use as a battery charger on a bank of 12V deep cycle batteries in my RV (440amps).
Power supplies are cheap and plentiful, 12V battery chargers are not.
I plan on connecting several to charge at a minimum of 100 amps, preferably much more.
Surely these things can be easily adjusted or tricked to up the voltage.
Any tips or ideas are much appreciated.

 

If i may suggest that since we are dealing with AC, this is one of those things that if you have to ask, you aren't qualified to be playing with it. Theres no way i would ever tell anyone how to do this, just the risk of fire, ignoring risk of serious electric shock is too great to do this. Computer power supplies are not rated for very many watts, you'll find that you'd need a substantial bank of modified supplies to handle 440 amps of batteries anyways. Major loss of effeciency.

You're on the wrong forum for this, but i'll give you some hints. You cant send 15V continiously to those batteries, you'd blow the cells. You DO need to find a "pulse conditioner" (sometimes called a desulphator) that will periodically raise the volts up to 15V to knock off the lead sulfate that will accumulate on the plates. You have too many cells for a single cheapo version. As you well know, that bank of batteries was not cheap. You want a nice one to do high freq and voltage pulses to keep them well conditioned, or you are going to pay on the backend when you buy new cells in a year.

I would strongly advocate you do some research on the web to find a high quality model and how to use them. If you are still feeling cheap, harbor frieght, northern tool and TSC all sell el cheapo chinese knockoff models.

 

Well, I did say any tips or ideas, but I wasn’t expecting to be insulted. Thanks.
I am qualified to play with it, I just don't have a schematic for one and decided I'd ask here first rather than destroy one or more trying to figure it out myself.

I don't plan on charging continuously, if you read "100+ amps" you would realize that. Btw, 15V or more will not hurt the cells as long as you don’t pump high amps into it after it’s fully charged. An amp or two at 20V won’t hurt a large lead/acid battery.

“Major loss of efficiencyâ€?? I don’t know of anything more efficient than a computer power supply, enlighten me. Not that I’m worried about efficiency in this case, but I’m still open to suggestions.

My battery bank was $240 new, I’m not going to spent $1000+ for a charger. My existing charger is only 30A and retails for $300. It was free to me since it didn’t work when I got it. The power supply in my computer is rated at 25A and was $20. Simple math, just need a few more volts to get the current flowing...

 

Wasnt trying to insult you. AC can kill you, fire can kill you and destroy property. The amount of current you are wanting to generate will kill you and burn your RV down to the wheels. If you are offended that I assume you don't know anything about what your asking, its only because I dont want to see you die while making the thing.

ATX
http://www.pavouk.comp.cz/hw/en_atxps.html
http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf
AT
http://home.tiscali.be/decoy/Electronics/at_ps.pdf

re:Major loss of efficiency- You'll need to come up with a way to convert the power to the voltages you desire, either by modifying the secondary windings or some step up circuit capabile of handling however many amps (usually less than <18) that transformer can output. With all that conversion, your probably going to end up at 30% efficiency. To do it right, youll also need to design an adjustable set point circuit to deal with the ambiant temperature and find a component PWM controller to handle the trickle.

I've fooled around with solar power, 24V and 48V systems, but 250$ for 440 amp hours worth of 12v deep cycle cells is a great deal, you made out like a bandit! Most of the stuff i've looked at is 1.50-3$ an amp hour.

Hope that helps you.

 

Thanks, this is helpful. I couldn't get a reponse for schematics from all the mfg's I emailed. Of course this is not the exact schematic I need, but still very helpful because I'll bet they're all similar in design.
Thanks, but don't worry about my safety. A power supply is harmless in my hands, fire is also a zero hazard in this particular case.

I'm still don't see why I'd lose efficiency, but not a problem if I did because my power source is a 7500W generator. Also, no need for tricke or temp adj, this setup is for fast charging in the field. I do not want a taper charge either, just full power until I turn it off.

Costco deep cycle batteries, 110A for $60ea. Four batteries power everything including the engine. Generic lead/acid w/ loose plates, but worth the $. As it is now with my 30A charger I need to run my generator for 10 hours minimum to recharge, I want to cut that down to 1 or 2 if possible.
High output transformers are very expensive, that's why converting a power supply looks appealing to me.

Thank you for your time

 

Dear Mr. Know it all chevota.

I HOPE THE HELLO you NEVER have to find out differently

I was a Firemam at one time. So I can HONESTLY say that.

" Anythings of an electrical nature IS or can be a FIRE hazard. "

And your remarks about inslults are WAY out of line.

When you come to a site like this you need to be prepared for ANY AND ALL kinds of answers. Some you may not like. Some may not even fit. But should be aware of and prepaired for this.

BillyBob

 

Chev,

Try these links. I agree with the fire hazard and the possibility of an explosion.

http://www.1st-optima-batteries.com/deep_cycle_battery.asp

http://www.crew6.com/battery-charger--battery-charger-schematic

http://www.pipox.com/battery-charger--battery-charger-cb-2ls

You might be able to get some info from these sites.

George

PS - Based on your apparent knowledge of certain things, I feel I can safely assume you DO have an appreciation of the fact that AC & DC voltage can kill.

 

Thanks, but there is no risk in this situation. To set everyone at ease, my experience and knowledge of electricity far and away exceeds that of the average person.
If you only have negative things to say, or want to preach your wisdom, please, don’t bother. It’s a waste of everyone’s time.
Thanks again JoeHobart for the links. I’ve been sidetracked but I will play with this eventually.

 

chevota, Although I admire your novel approach on this, I'm afraid you will fail to pull it off. The main reason will be because computer power supplies are not suitable for parallel connecting. The second reason will be because computer power supplies are not rated for a 100% duty cycle. Their U.L. approval is for a Definite Purpose Device that has been demonstrated to function in a very well defined set of circumstances. Lead acid battery charging has very different requirements as well as some special safety measures that are required to protect against loss of life and property.

I won't belabor the safety issue any more.

Revisiting the first issue I mentioned, parallel connecting the supplies, since these are very closely regulated supplies and use zener diodes for feedback biasing the system to control output, any parallel voltage source will interfere with that control. The various paralleled supplies will take turns shutting down as soon as they detect the voltage output of one of the other units. This phenomenon will occur many times per second and true control will be completely lost. The supplies will then either heat up beyond their normal operating range or shut down to a very low output.

In addition to that, paralleling lead acid batteries can also be disappointing since the charging current tends to go to the battery with the least internal resistance. Unfortunately that is the one with the highest state of charge. That's exactly the reverse of what you would like to happen. To overcome that, you could incorporate diode switching into the system but that cost more money. We haven't even considered how you intend to increase the output voltage to the potential necessary to charge a 12 volts battery to a full state. As you have indicated, that takes around 15 volts. Since the maximum voltage of the computer power supply is determined by a transformer, you would need to either replace it or add a boost transformer in series. That's more money. That's not to mention that you would then have to change the zener diode circuitry to accommodate this new initial voltage as it affects total current output. Now that you have faced the issues and realize that changing all the insides of the power supply would in fact mean you're not really using much of the original beyond possibly the case itself.

I'm sorry I can't give you any encouragement but the fact is, battery chargers are cheap, crude, durable devices when compared to computer power supplies.

Best regards.

 

Battery charging is simple.
When I'm done with it there won't be any zeners or other circuits to worry about, but that would be a given.... Chargers will work fine in parallel.
Batteries in parallel is also fine, especially a non-issue at high current like I stated I was looking for.
I only glanced at the schematic, but my first idea was to combine the 12V and 5V outputs together. When I tear one apart I’ll look into it further.
High output battery chargers are NOT cheap.

Thanks for the positive input.

 

Good luck. Post back your findings so that all may share the process. I'm sure others have had this idea as well.

There is an axiom in electrical engineering that goes something like this - "The less copper the less robust." You're just buying more copper when you get a battery charger. You may think that a computer PS will output 350 watts which would yield 29 amps @ 12 volts but you have only to look at the wire size of the output wires to realize that it wouldn't handle that current without melting the insulation. That would require a minimum of #10 copper with high temp. insulation as opposed to the 16 gauge that is normally used. They generally run about 5 amps output under normal usage, and possibly 20 amps short term peak. To get the amps you mention will take quite a few of these units.

 

Thanks for the post surferdude.

That makes sense for sure, that’s why I’ll need several. I figure I’d draw the line at 10-12 units.
So far the best transformer I can find (amp-pound ratio) is a 30A job that only weighs about 8lbs, unfortunately it retails for $300. I’ve considered large transformers like the one in my 225A Lincoln welder, unfortunately its 100% duty cycle is way down at 75A, and since it weighs about 150lbs, it’s not an option.

Have you ever seen an inverter? Nice little deals that are basically the reverse of a computer power supply. I have several, one is rated at 2000W continuous, that’s about 170A of draw from a 12V battery. If you look at the insides you’d say no way (like I did), but it handles it. I could rewire it to be a power supply, but it was expensive and I need it as is. "Bad" power supplies are free and no loss if I let the smoke out. The bad part is almost always some little component I wouldn't need, not the transformer(s).
I’m not saying this will work for sure, it may simply not be worth the effort but I figured it would be worth a look. If I really can squeeze 25A from one then I’ll be a happy camper for sure.

Another option I have seriously considered is to dissemble my 240V generator and tap the windings for about 18V. I figure it’s good for over 400A, but like my inverter, it’s new and expensive so I’m looking for other options first.

Yet another option of is just mount a couple of modified alternators to either my generator or the engine in the RV. I figure $100 per 100A alt and a custom mount.

 

I am very sorry to read that taking someones personal saftey and well being into consideration is a waste of time.

BillyBob