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Electronics => Projects, Designs, and Technical Stuff => Topic started by: TheAmmoniacal on September 02, 2014, 09:42:04 am

Title: M8 constant current electronic load the V6 version discharger
Post by: TheAmmoniacal on September 02, 2014, 09:42:04 am
I'm looking for a cheap small device that would let me test the full capacity of my batteries/battery pack. I'd love to have a real electronic load, but considering I already have a datalogging multimeter (and not much money), a simple constant-current load would be fine. While looking around I found this small circuit:

http://www.aliexpress.com/item/Free-shipping-new-M8-constant-current-electronic-load-the-V6-version-discharger-discharger/1158031597.html (http://www.aliexpress.com/item/Free-shipping-new-M8-constant-current-electronic-load-the-V6-version-discharger-discharger/1158031597.html)
http://www.ebay.com/itm/new-M8-constant-current-electronic-load-the-V6-version-discharger-discharger-/321216410343?pt=LH_DefaultDomain_0&hash=item4ac9fd72e7 (http://www.ebay.com/itm/new-M8-constant-current-electronic-load-the-V6-version-discharger-discharger-/321216410343?pt=LH_DefaultDomain_0&hash=item4ac9fd72e7)

From what I can understand this circuit seems to be exactly what I want, but I can't entirely understand what it does or how it works. I'd like to ask if any of you understand more of what this circuit does, and if it works for my needs?

As far as I can understand, the device allows me to connect a dummy load and my battery, but how would it draw a constant current from that? Does it boost the voltage to match my load's resistance?

Any more explanation would be helpful, thanks.
Title: Re: M8 constant current electronic load the V6 version discharger
Post by: cowana on September 02, 2014, 11:06:33 am
The three terminal device mounted on flying wires is a K1450 N Channel MOSFET. This is connected across the supply, and the controller sets the gate voltage to ensure the desired current is drawn (and thus dissipated in the MOSFET). This means the MOSFET will get very hot - and certainly need to be mounted on a large (and possibly fan cooled) heatsink for anything but the smallest (<1W) of discharges.

Andy
Title: Re: M8 constant current electronic load the V6 version discharger
Post by: TheAmmoniacal on September 02, 2014, 11:11:55 am
If that's the case it won't be very useful, I'm thinking of dissipating in the order of 40-70 W.
Title: Re: M8 constant current electronic load the V6 version discharger
Post by: cowana on September 02, 2014, 11:30:17 am
If you mount the MOSFET on a computer's CPU heatsink along with a fan, you shouldn't have any issues is dissipating that sort of level of power from it.