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60 Amp 12 VDC "Portable DC Supply"

Old 09-14-2011, 11:56 PM
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kyleservicetech
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Default 60 Amp 12 VDC "Portable DC Supply"

I've been flying electric models now for some 30 years, starting off with rewound motors from work, progressing through Astroflight brush and brushless motors, to the Hacker brushless motors now in my models.

Along with this, is five 6S2P A123 packs, two 4S1P packs, and one 6S1P pack. Charging these batteries eventually wound up with the Cellpro Powerlab 8 charger, a very fine charger that can pretty much charge anything out there.

But, that giant scale model of mine uses 24 A123 cells configured as a 12S2P pack in flight, and as 6S4P pack for charging. The DC supply is a PAIR of 120 Ampere Hour deep cycle batteries connected in parallel.

That Cellpro '8 charger pulls 40 Amperes out of those deep cycle batteries, and in doing so, reduces their ampere rating to much less than 120 Ampere hours, because of the high drain of the Cellpro charger.

By count, I've now gone through FIVE of those 120 Ampere Hour deep cycle batteries in the past four years! The last day of flying got just one flight on the 12S2P pack before the two deep cycle batteries went flat.

These deep cycle batteries have been well maintained, always recharged after flights with a deep cycle battery charger, always had proper water in the cells. But in my experience they just don't hold up.

Thought about those gulf cart batteries, but needing two at $100 plus each, and not knowing if they can handle a continuous 40 ampere drain made that a questionable solution. Even looked at those giant truck batteries, but it would take a crane to move one out of my pickup truck.

So, the "portable 60 Amp 12 VDC charger" was built. Yup, it is noisy, it smells so you can't run it in your home. But as long as it has gas, it will provide those 60 Amps all day long.

Wiring up this unit is fairly straight forward, requiring only a toggle switch to kill power from the battery to the alternator when the engine is not running.

The engine is an old but reliable 3.5 HP Briggs and Straton Engine, the alternator is a Delco 7127-3, purchased as a reconditioned unit for about $70, including the required core deposit. The lead acid battery is a cheap garden tractor variety for about $20.

As for weight, the two deep cycle batteries weigh in at 134 pounds together, as compared to 41 pounds for the engine/alternator combo, plus a few more pounds for the small lead acid battery.

The engine has a computer controlled timer on it that times out and kills the engine after 30 minutes. Only limit to maximum charge rate is the engine itself. Much over 60 amps and the engine runs out of power.

Take a look, next project is to put a belt guard on the pulleys. (It now has a belt guard on it!)
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Last edited by kyleservicetech; 09-30-2011 at 10:02 PM.
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Old 10-02-2011, 07:04 AM
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TheWoodCrafter
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That sure seems like a lot of work.

Wouldn't a generator have been cheaper and easier?

Or don't you have a power supply?
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Old 10-03-2011, 12:35 AM
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CHELLIE
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Hi Dennis look into one of these battery zappers, they work great, they will keep your batteries from getting sulfated, I have one, and cant belive at how well they work, the battery in my friends truck was getting weak, and it brought it back to life, it will keep a battery going strong for up to 10 Years. Take care, Chellie

http://www.ebay.com/itm/Desulfator-B...item230b5657f8

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Old 10-03-2011, 02:44 AM
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kyleservicetech
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Originally Posted by TheWoodCrafter View Post
That sure seems like a lot of work.

Wouldn't a generator have been cheaper and easier?

Or don't you have a power supply?
Yup, I've got a power supply, in fact several of them from a dual 3 Amp 0-24 volt unit to a variable 0-24 Volt, 25 Amp unit. Thats only 600 watts.

Problem is, that Cellpro Powerlab 8 can pull over 1000 watts from a 12 volt battery, and 1000 watt powersupplies get expensive, real quick. Like $500 or more. Then you've got to buy the generator that can also put out 1000 watts. Another few hundred bucks.

I all ready had the Briggs Gas engine setup all welded together, only had to buy a $70 rebuilt alternator, plus a cheap lawnmower battery to work with it.

This unit charged up two models for six flights total today. But that Briggs engine went through near 1/2 gallon of gas doing it.

Oh well.
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Old 10-03-2011, 02:56 AM
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Your solution does work and very industrious on your part, for sure.

But 2 server PS to output 24V at about 1600W is less than $50 delivered to your door.

I don't know what the input on those would be maybe 15 - 20 AMPS 120V.

And a cheap generator is most likely just as noisy as you B & S.
Because the Honda generators are way too expensive.
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Old 10-03-2011, 03:13 AM
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kyleservicetech
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Originally Posted by CHELLIE View Post
Hi Dennis look into one of these battery zappers, they work great, they will keep your batteries from getting sulfated, I have one, and cant belive at how well they work, the battery in my friends truck was getting weak, and it brought it back to life, it will keep a battery going strong for up to 10 Years. Take care, Chellie

http://www.ebay.com/itm/Desulfator-B...item230b5657f8
Hi Chellie

This is the explaination on how that desulfator works from their website listed above:
"The Desulfator generates Amplitude Modulated Pulses (AMP) at the resonance frequency of the crystals to shatter the covalent bonds that hold it together. This allows the lead sulfate to be reconverted once the battery is charged. A battery free from lead sulfate crystals will have its lifespan stretched to its maximum! No more premature failure due to sulfation!"

The problem I've been having is those deep cycle batteries are rated for a 20 hour discharge time. And you're not supposed to discharge them much over 50% of capacity. I've been totally discharging them in three hours. That's really hard on them, they just don't stand up. Add to that they weigh 70 pounds. Each, and I've got two in parallel. Just getting to old to haul them around anymore!

Other internet sites on batteries indicate one way to desulfate a lead acid battery is to boost its voltage above 15 volts or more for an hour or so. Tried that, didn't work. My battery hydrometer shows that the battery is just dead. It would start a car, or truck, but trying to pull 40 amps out of it, the danged things last about 30 minutes or so after a season of flying with them. They were name brand batteries, not from Wallyworld.
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Old 10-03-2011, 02:59 PM
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Dennis,

Very neat idea. A portable power solution for the field. I like it. Big thumbs up for your design.

What some people fail to realize is that generators are expensive, and bulky to transport, and you have essentially made one from materials you already had. (minus the alterator) Ingenious.
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Old 10-03-2011, 06:24 PM
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kyleservicetech
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Originally Posted by idealhobbies View Post
Dennis,

Very neat idea. A portable power solution for the field. I like it. Big thumbs up for your design.

What some people fail to realize is that generators are expensive, and bulky to transport, and you have essentially made one from materials you already had. (minus the alterator) Ingenious.
Thanks!
Next step for a winter project, pull the gas tank and other stuff and give it a nice coat of black paint.

And, try it with a small gell cell that could be bolted to the whole thing, rather than that lawnmower battery.
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