Green Galaxy DC-DC converter inside

General Discussion about large electric scooters and motorcycles and other things with no pedals.

Green Galaxy DC-DC converter inside

Postby Njay » Sat May 14, 2011 8:46 pm

Got my hands on a cheap "Green Galaxy" (also known by other names) DC-DC converters" spec'd

Input voltage range: 30V - 60V
Output: 12V, 10A

to use on a converter motorcycle and did some tests. The purpose was to see how much power could I take from it and to change its output voltage to around 13.8V to charge a small on-board 12V battery. I ended up reverse-engineering the schematics to see exactly what it does. So here's the study result:

Output impedance: ~ 0.035 Ohm
Output voltage, no load: 11.84V

Tested up to 8A output for a few seconds; voltage falls linearly according to output impedance.

Image

Almost complete schematics (sorry for old-school hand drawing :)):

Image

Then I soldered a 5K6 5% in parallel with the 1K2 bottom output divider resistor to get the output voltage up to around 13.8V:

Image

Tested the converter @ 23ºC ambient temperature for one hour running at 70W output load, and the box gets finger burning hot (over 60ºC), so I won't recommend using it continuously for higher power than this without "active" cooling.

Update:

Typical output ripple:

Image

I haven't tried yet, but it seems that these converters, being "current mode" converters, can have their outputs connected in parallel and will share the load.
Njay
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Re: Green Galaxy DC-DC converter inside

Postby TonyReynolds » Wed Mar 21, 2012 9:58 am

I wonder if it would produce as much heat for me going from 52V to 12V?
Third Build: 2012 Marin Muirwoods 4130 Cromoly, 7 speed 11/32 with 500/1000W MAC geared rear motor, 48V System, 52V, 11.5Ah 16s5p A123 lifepo4 triangle battery, DP CA; 20-30+ MPH... GRIN! Build Thread: http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=33819
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Re: Green Galaxy DC-DC converter inside

Postby Njay » Fri Mar 23, 2012 5:25 am

Heating depends mostly on the output current... These converters can be found for $25 in some places, last time I saw.
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