Home-brew battery measuring station

[BrianG]

Originally Posted by himalaya

Great thinking Brian.

I am worrying about the MMM's input decoupling capacitors, you are pushing them really hard by this app.

IMO a programable(or just use a potentiometer to adjust) linear current source would be just fine for this application. just get a few power MOSFETs mounted on a HUGE fan-cooled heatsink, drive them with an Opamp connected as a current source, that's it.

You know what a stable and constant current means for a battery test platform, right?

Yeah, I was thinking about the caps too, and was going to add several more (probably another 2000uF or more). Being a resistive load though won't have that constant ripple which heats them up, at least not as much as a motor's inductive load. I do still have to take the MMM's PWM switching into consideration though.

From some research on using FETs as a pass transistor for a high-A power supply, it takes a special type of FET (read: expensive) to operate well in the linear region (as opposed to switching). FETs would be easier to parallel though. So, that leaves paralleling a bunch of transistors - ugg. I'd need a "few" to say the least!

Originally Posted by hoober

I've offered to test batteries on a few forums before up to 500 watts. I have one cc-400 and 1 cba that is paid for already. It produces nice repeatable graphs , but no-one seemed interested enough to send me any packs.

I know you like to invent/engineer/build stuff , but my point/question is how much are you looking to spend on labor/equipment? This set-up seems available for about $1 per watt, maybe $500 total and can add multiple cc-400's at about the same $ per watt.

I figured it this way: I had already paid for the test equipment and didn't want to buy batteries. I thought perhaps users may send battery samples, but shipping twice really comes close to some of the battery packs I'd be testing. So then I'm left with simply buying the packs myself (packs I don't need)

We've talked about standards too, I can't remember which forum. I kinda like testing single cell for direct comparison , but doing "packs" seemed to be the choice of many users even though it requires 2,3,4,5,6 times the power.

Looking forward to the results here for sure. Someone send me a "test" pack, so I can pull the equipment out of the box ,lol. I don't think there will be any credibility issues with your testing/graphs/data/info Brian.

That type of device would be the ideal platform since that is what it was designed for. My idea was just based off things I have or can get fairly cheaply. If testing single cells, 1 or 2 of those would be sufficient power-wise.

I too am concerned about getting enough interest to justify the cost/bother of assembling this (although I could use it for my own uses too ). What we really need is to set up a company that does this "right": manufacturers send in sample packs, pay a certain fee, and we provide them a "birth certificate" (similar to some car audio amplifiers) outlining its performance over a variety of tests that they can use in their advertising. Voila! A third party unbiased testing result!

Originally Posted by Arct1k

http://www.powerohm.com/catalog/GRCAT00.pdf

RH350?

I just sent in a quote request for the 350, but I would speculate that just the resistor is well over what I want to spend on this project.

For all the parts and components, I can see about $500 if I can find good deals. I have some stuff already. I have a watch on an eBay auction of 240 Dale 50w power resistors (3 ohm).

Thanks guys! Keep up the feedback. Maybe there is a better and cost-effective way to get us the data we all want (but few realize they want it).

[himalaya]

Originally Posted by BrianG

From some research on using FETs as a pass transistor for a high-A power supply, it takes a special type of FET (read: expensive) to operate well in the linear region (as opposed to switching). FETs would be easier to parallel though. So, that leaves paralleling a bunch of transistors - ugg. I'd need a "few" to say the least!

.

ANY power MOSFET can do this, as long as you can take their heat out. You don't have to take care of the FET linearity, the OpAmp will do. If you need I can draw a basic schematic for yoru ref.