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Mar 05, 2004, 10:52 AM
Registered User
Radiofly's Avatar

Universal power supply for motor testing?


I would like to get real world baseline measurements for various motor/prop/airframe installations. Batteries are inconvenient for testing purposes, due to power fluctuations and charge/recharge cycles. So, I'd like to get a variable DC power supply to facilitate testing motors, props, and airframe interactions. I'd like to get something to test up to about 250W motors.

Analog power supplies in the 25-30 amp region cost about $400 or much more. Switching power supplies are less expensive. I think a variable DC switching power supply is Ok to use with electric motors and their ESCs so that may be the least costly way to go.

Has anyone out there rigged up an inexpensive test station? Willing to show pics and details?
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Mar 05, 2004, 11:40 AM
Supersonic Engineering
GordonTarling's Avatar
While a switching power supply MAY work with brushed motors and ESC's, don't even think about using one for brushless - you'll fry either the ESC or power supply or both in very short time!
Mar 05, 2004, 11:58 AM
Registered User
Thank you, Radiofly, for bringing up the subject. And thank you, Gordon, for your response. I was just getting ready to order a variable voltage/current power supply for the dual purpose of charging Li cells and bench testing both brushed and brushless motors. All of the power supplies I am looking at are switching. It would have been a huge disappointment to spend a lot of money on a variable switching power supply and learn afterwards that it could not be used to bench test brushless motors!
Mar 05, 2004, 12:29 PM
Registered User
Radiofly's Avatar
I'm glad I asked, too. Thanks Gordon. I wasn't really aware that a switching power supply would be a problem with brushless. Is this due to phase interaction between the switching frequency of the power supply and of the brushless ESC?
Mar 18, 2004, 08:24 PM
Registered User
Radiofly's Avatar
For the sake of general interest, I kept wondering why a switched power supply might not be good to use with a brushless ESC. I did contact some ESC manufacturers. They said that a switched power supply would be just fine. Good to know because they are so much cheaper than a capable analog (i.e., linear) supply.
Mar 18, 2004, 08:34 PM
T:W>1= :>)
rc-eflyer's Avatar
Quote:
Originally posted by GordonTarling
While a switching power supply MAY work with brushed motors and ESC's, don't even think about using one for brushless - you'll fry either the ESC or power supply or both in very short time!
Why?
Mar 19, 2004, 04:32 AM
Registered User
vintage1's Avatar
Quote:
Originally posted by GordonTarling
While a switching power supply MAY work with brushed motors and ESC's, don't even think about using one for brushless - you'll fry either the ESC or power supply or both in very short time!
Why? They are just a DC source, same as a battery...

You might need a bit of capacitor at the end of long test leads to make sure the lead inductance doesn't cause problems tho.
Mar 19, 2004, 07:40 AM
Crash Master
Gene Bond's Avatar
Assuming the ripple rating is reasonably low, which it should be on any power supply, a switcher should be no different than a linear. The real difference is in the conversion... Linears dissipate more heat, and are considered more accurate, since there is not a filtering/conversion done after the voltage regulation section. The switchers have more capacitors to filter the input to the power transistors and then again after. The linears have more heat sink to dissipate the high loss of the power transistors.

Again, assuming a quality power supply, there should be no real difference in ripple, which is the significant problem for ANY esc, not just BL.
Mar 19, 2004, 07:53 AM
Registered User
What protects the power supply from motor start-up surges and reactive loads? The ESC?

- RD
Mar 19, 2004, 12:41 PM
Trying to defy gravity...
jimsky's Avatar
A properly designed power supply (reguardless of conversion topology) should be immune from short circuiting and typical transient conditions one would encounter during "reasonable" operation.

Look around on eBay for used adustable voltage/current benchtop power supplies from manufactures like Lambda, Sorensen, HP and the like. I recently scored a nice used Lambda LP Series power supply. Just the ticket for doing motor/prop characterizing work.

Jimsky
Mar 19, 2004, 02:13 PM
Registered User
WJ Birmingham's Avatar
Granted we only used it up to 16 Amps, the Kosel power supply we purchased from www.Ramboy.com worked just fine, hooked directly up to the Phoenix 25.

I'm not power supply literate, so I dont know if a Kosel is switched or linear.

WJ
Mar 19, 2004, 02:36 PM
Trying to defy gravity...
jimsky's Avatar
The Kosel is a "switcher". If the small amount of output voltage adjustment capability that is provided is acceptable for your usage (and an adjustable current limit is not required) than this is a very cost effective solution.

Jimsky
Mar 19, 2004, 05:03 PM
Supersonic Engineering
GordonTarling's Avatar
Sorry, chaps, I'm not a technical expert on these matters, but I was clearly told by Matthias Schulze himself (who should know his stuff!) that a power supply should not be used for supplying a brushless ESC and only to use a battery. I think it's something to do with the high voltages produced by the switching transients due to lead inductance, but I could be wrong. Perhaps this only applies to Schulze ESC's ?
Mar 19, 2004, 05:27 PM
Registered User
RagnarA's Avatar
With due deference to Mr. Schultze( I have one of his 330d's) I am a ham radio operator. If a switching or linear power supply was going to fry a $60 esc, it'd fry a $500 ham transciever or a $1500 base unit. I routinely use a MFJ 25 amp variable voltage switching power supply for all ham and RC radio uses (testing). The problem is going with the cheapest power supplies that lack adequate filtering. Also in older units, the capacitors in the filtering circuit can break down. I've read a discourse by Mr. Schultze where I believe he points out that is the problem. If I wanted a 0-30 volt, 40 amp supply, I'd probably use a Dymond Ham Radio power supply. Last time I checked it was about $189. I bought a new lab quality, digital Chinese linear power supply a while back, just for testing and large lipo pack charging purposes. MFJ's good, Alinco's good, Dymond's good, etc. Samlex will work. Check with Ham Radio Supply Houses. I got my Chinese digital unit off Ebay, new, about 1/5 the cost of a used Hewlett Packard. If you use a really cheap and dirty power supply for a charger, put a 12 Volt, lead-acid storage battery between the power supply and the equipment, will filter the output, but only works for 12 volt applications. Cheers.
Mar 19, 2004, 05:34 PM
Registered User
WimH's Avatar
Quote:
Originally posted by RD Blakeslee
What protects the power supply from motor start-up surges and reactive loads? The ESC?

- RD
a sizeable capacitor like on the Torcman teststand ( the black thing on the right hand side) should do the trick:



and it is to protect the esc , exactly like vintage said.
Last edited by WimH; Mar 19, 2004 at 05:37 PM.


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