Power Supplies with Battery Backup

[BengalBeaux]

I'm wanting to build a standby power system for my home with items I happen to have on hand, which are, a couple deep cycle 12 volt batteries, an 800 watt continuous load AC generator, a 2000 watt DC/AC inverter, and quite a few old computers.

I want to use the inverter to power the home because it will allow me to start and run larger loads for short periods of time; however, I estimate my average standby power usage during a power outage to be only 500 watts (so the generator has enough capacity).

My idea is to parallel several of the 12 volt power supplies from the computers and run them off of the generator to provide approximately 13 volts and 60 amps of power to the inverter. I also want to provide parallel power to the inverter from the batteries to kick in when my AC loads exceed 800 watts.

Will this work, or will my power supplies try to provide all of the power and overload?

 

[waross]

I would suggest that you may have better results if you use the batteries to run the inverter. Then use the generator to charge the batteries. This may be done simultaneously.
I am not sure about the feasibility of running computer power supplies in parallel, or the possibility of getting 13 or 14 volts out of them.
If you have old auto parts available, consider using an old automotive alternator belted to the generator engine to charge the batteries. You will avoid possible issues with: power supplies running in parallel, peak voltage available to the power supplies and frequency stability.
respectfully

 

[itsmoked]

You will not;
1) get those PC supplies to provide the correct output power.
2) get them to work in parallel.
3) get them to not miss-charge and therefore ruin the batteries.

waross has a good idea. Get a car alternator running to charge the batteries. Then run your house stuff always with the inverter.

Or get a proper charger and run that with the generator to charge the batteries.

Or get any ONE power supply(not PC) set to the precise voltage required to "float" charge the batteries.(See battery manufacturer float voltage){don't forget to put in a current limiting resistor between this supply and the batteries to protect the power supply.}

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[BengalBeaux]

Using a battery charger was my first choice, but today's battery chargers all seem to have smart charge technology and I haven't seen any of them that tell me what their output voltage is (only that they will charge at a specified rate of current). My concern is that the charger will output a DC voltage in excess of what the inverter will accept.

I suppose that I could link an automobile alternator with a voltage regulator up to an AC motor being powered by the generator, but I'd rather not be bothered with the moving parts.

Thanks, both of you, for your help in at least letting me know the idea that I had with the computer power supplies is not feasible.

Jeff

 

[itsmoked]

You do not have to worry about a charger over-volting your inverter. NADA!

The biggest problem is that most %90 of the chargers do not understand that the battery has or has no load on it which confuses the charger into making wrong assumptions. This is why a fixed supply with an appropriate limiter set to float works the best.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

I wouldn't try to drive an automotive altenator with an electric motor except as a last resort.
I would try to adapt the generator engine to drive the alternator directly with a belt.
My second choice would be the battery charger. Be aware that the charger may be somewhat frequency sensitive. It may also be dependant on the peak voltage output from the generator.
A small generator often suffers a reduction in both peak voltage and frequency when it is loaded.
Itsmoked; I welcome your additional comments as to the quality of battery charger that may be required to operate efficiently on a small generator. The very cheap and simple battery chargers do not perform well on reduced input voltage. You probably know better than I, what is available in the more elaborate designs.
Thanks
respectfully
PS; I don't rule out a motor driving the alternator, just give it third place. The economics of your project and the ready availability of parts may move the motor driven alternator into the first place choice.
r

 

[BengalBeaux]

I've emailed several battery charger manufacturers for their suggestions. Schumacher is a manufacturer that makes manual chargers which I think may do the trick.

Disassembing the AC generator and connecting an alternator to it is not something that I want to do. It would void the warranty and I also like to use the generator as it is for football tailgating. I'd be more apt to find a discarded lawnmower engine to drive the alternator if I didn't use an AC motor (probably from a discarded washing machine).

Heat is also a concern because these items will operate in my garage and I live in Louisiana. That was a big part of the allure to the computer power supplies, because they are switching type supplies that run cooler and also have a good size fan attached to them. Because of this, I think I could keep them cooler.

I guess the number one idea at the moment is a Schumacher manual charger that can output up to 40 amps and has a cooling fan. I expect that if this thing runs in a mechanic shop, it'll run okay in my hot garage. I've also looked at some various high power output ham radio power supplies but I'm concerned about the heat (I also don't need all of the filtering).

Thanks again to both of you for your input.

 

[itsmoked]

I'd check the surplus places for a 15V power supply that can be adjusted. I don't think I'd bother with a charger. But what the heck, there are some great chargers out there.

You have said something scary.. Running any generator in a garage is a great recipe for killing your family.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ScottyUK]

A word of warning about washing m/c motors: if they are from any m/c of recent vintage - 1990 onward, maybe earlier, they are awkward motors with at least two combinations of poles, or a pole switching design, to give multiple speeds. They usually have a tacho too. If you can salvage the control electronics (which will almost certainly be potted in resin) and work out which terminals are inputs and which are outputs, you may have a chance of using one. Laundry dryers usually contain simpler motors.


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I don't suffer from insanity. I enjoy it...

 

[BengalBeaux]

ItsSmoked, I appreciate your concern and words of caution, but don't worry. I used the term garage liberally; a better description is a shed or storage area that is detached from the house. It's also not nearly airtight enough for air poisoning even if you close the doors and stand in the shed with the thing running.

ScottyUK, the problem with a dryer motor is that most run off of 220 and I only have a 110 supply. Thanks for enlightening me regarding the variable speeds on the washing machine motor.

It looks like for the time being (in event I need power), I'll hook up the Schumacher 40 Amp manual charger to the batteries which should offset the amount of power I'm using. Down the road, I may make up one of these contraptions from an old lawnmower engine. (see below website link)

http://theepicenter.com/tow02077.html

As always, thanks for your input and suggestions.

 

[itsmoked]

Sounds good! Take care.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com