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Old Dec 05, 2003, 02:51 PM
BillBrian is offline
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Question

Power Supplies for Testing Electric Motors in a Test Stand


I am designing an aircraft and want to test the motor and craft's stability, thrust, etc., in a test stand and power the motor with a tethered power supply so that I don't have to worry about recharging the batteries while I configure and tweak the assembly. Does anyone have any experiencxe/suggestions for what would work well for a power supply. I was thinking about using 12 volt car batteries or a battery charger to inout into the controller. I would also like to supply 2 electrics. I'm looking to use about two 1/2 hp motors in the craft. Would I be better off using the car batteries or could I bypass the batteries and use the charger supply directly- I would choose a motor that would run effciently with 12 volts each, hence two chargers or two batteries.

Thanks,

Bill Brian
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Old Dec 05, 2003, 04:17 PM
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Just off the top of my head, I think it would be hard to find (and expensive to get) a dedicated DC power supply which could provide a current in excess of 30A [and you'd need two of them] - I have a RadioShack 13.8V/10A supply, but the largest I've seen in our store was only 15A. Big deep cycle marine 12V batteries should do the trick.

Cheers, Phil
Old Dec 05, 2003, 04:37 PM
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Thanks Phil,

I have found 30 amp battery chargers on sale for $59.99. They are the kind on wheels that you get from an auto store. I don't know why they wouldn't work? Do you?

Bill
Old Dec 05, 2003, 04:52 PM
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Chargers don't supply DC, only rectified AC. They may work if you get them to charge an auto battery, and take the power from the battery. This limits you to 12V - Ie 10 cell NiMH flight packs.

But I'm afraid you are using a hammer to crack as nut. Running motors for more than a few seconds on a bench is likely to overheat them, and your flight battery should be more than enough for that. If you want to measure static thrust you can do that in a few seconds, but most modellers find it a waste of time as it doesn't give info at flying speed (except for hoverers).

Neil.
Old Dec 05, 2003, 05:16 PM
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Yes, hovering is the application and we need time to test. We don't expect to run it at full throttle very long, but we hate the thought of changing out batteries--and we may not have enough thrust to lift batteries and everything else until we scale up the model. We are experimenting and want to keep our costs down in the early concept testing stages. Tethering simplifies--sounds like we need to use batteries and limit the amperage to keep the motors from overheating???

Thanks
Old Dec 05, 2003, 05:43 PM
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I have an Astron 50 amp supply but it was expensive. There is another thread about this.
Old Dec 05, 2003, 08:20 PM
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With a cheap trickle charger and a decent car battery you can run your motors for "a short time" no problem. You could even leave the battery in the car (really cheap) if you had enough lead.
Use your instrumentation to measure Watts/Amps input and stop after a few seconds to take temps. "Sneak up" on your test points carefully and you can avoid letting the smoke out.
Be careful. Yesterday while running up a 110W system, I noticed sudden quietness and simultaneous lightness of the new plane I was holding. A quick look around revealed my homemade mount failed and the motor/gearbox/prop/esc were about 10ft away. It happened instantly. One moment running at 110W the next all quiet. No damage to people (glad I was outside) or plane. I was embarrassed about the failure though. Next generation will be way overbuilt. I hope.
Old Dec 07, 2003, 05:48 PM
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Bill. The astron power supply is a fine unit. I run one on my Ham Radio Station and it will deliver 35 Amps all day. If you want a lower cost power source I wound get a deep cycle battery. I have a small deep cycle golf cart battery in my field box and I have never ran it down at the flying field charging my batteries at 6 amp. The only draw back with a deel cycle battery is they need to be charged wtih a special 1.5 amp charger if you want it to last for years and they are heavy. Hope this helps.
Old Dec 07, 2003, 06:02 PM
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They're pricey, but something like this would be ideal.
Variable V output, up to 28A.

http://www.bkprecision.com/www/np_specs.asp?m=1690
Old Dec 07, 2003, 10:26 PM
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The point that was raised earlier, but appears to have been overlooked, is that you should not run a power system on a test stand or similar for more than a few seconds. This is the quickest way to overheat and destroy electric propulsion system components. There's no amount of "tweaking" that requires a power system to be run for more than a few seconds at a time.
..a
Old Dec 08, 2003, 01:10 AM
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Re: Power Supplies for Testing Electric Motors in a Test Stand


ASTRON Makes some power supplys that we use to test all our speed controls 0~18 V 0~100 AMPs
Do a web search for astron power supplys
Ken


Quote:
Originally posted by BillBrian
I am designing an aircraft and want to test the motor and craft's stability, thrust, etc., in a test stand and power the motor with a tethered power supply so that I don't have to worry about recharging the batteries while I configure and tweak the assembly. Does anyone have any experiencxe/suggestions for what would work well for a power supply. I was thinking about using 12 volt car batteries or a battery charger to inout into the controller. I would also like to supply 2 electrics. I'm looking to use about two 1/2 hp motors in the craft. Would I be better off using the car batteries or could I bypass the batteries and use the charger supply directly- I would choose a motor that would run effciently with 12 volts each, hence two chargers or two batteries.

Thanks,

Bill Brian
Old Dec 08, 2003, 08:13 AM
Arizona Chuck is offline
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I use a low Tec. approach to testing. I test the amperage with a watt meter, then hold the plane up, give it full power and ask myself "will this fly".
If it will go up if I let go, then it will hover.


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