Battery Analyzing with Graphs
 

Picked up a BD250 for more convenient discharging, and figured I'd give the software a test drive. At first glance, it seemed pretty useless, but then I realized I could run some tests to see how my batteries fare over a discharge cycle with it. I've been curious to see how my 4800 race pack stacks up against my 6100's for 17.5 off road racing... Trying to find out if the weight penalty worth the higher sustained voltage.

Test setup:
Balance charge packs to 4.2V/cell on my 408 duo @ 20A , then discharge at 5A to 3.5V/cell
Batteries Tested:
Reedy Zappers 4800mAh SG4 - IR 2-3 mΩ - 204g
Reedy Zappers 6100mAh SG4 - IR 2-3 mΩ - 215g
Reedy Zappers 6100mAh SG3 - IR 2-3 mΩ - 215g

I wanted to do a higher amp discharge more reflective of race conditions, but the 30s data interval limit of the software doesn't give enough resolution, and the voltage crashing could skew data a bit more.

Results:
https://cimg1.ibsrv.net/gimg/www.rct...d1be712f7f.jpg

Has anyone else seen or done similar? It seems like the ~11g weight penalty is worth the 0.1V benefit of the higher capacity for stock racing.

Is the BD250 capable of a 5A discharge on 2S? The Manual states that the range on 2S is 29.76A - 35.00A

That was the main reason I haven't purchased one because I didn't always want to discharge at 29.76A on 2S.

Says 0.01A - 35.00A here. Also, a minimum of 29A wouldn't make any sense IMO.

A 5A discharge isn't very useful since it's a fairly low current. Looks like your batteries took almost an hour to discharge at this rate.
A higher discharge will be more helpful. And while a 30 second interval isn't ideal, it should still give you plenty of data. I test my batteries with a 5 min discharge and then sum up the voltages at 1 minute intervals. Or you could just take an average. For me a battery that holds a higher voltage over 5 minutes should outperform one with a lower voltage.

There is one other aspect that isn't taken into consideration with this type of test and that's battery punch. I built an arduino battery monitor that reads voltage before and after a 2 second high current discharge that I apply with a full size car battery tester. The setup is not ideal, but it allows me to see how a battery with a lower IR but lower capacity performs against a higher IR/larger capacity one. SMC Racing does something similar with their Power Factor tests.

Yes, the website shows a range of 0.01-35.0 A. Using your link, if you scroll down lower, there is a table, and it says: "Min. Discharge Current (A)" and across 2S Lipo, it shows "29.76" which implies that the minimum discharge current on 2S Lipo is 29.76A. With a Max of 35.0A

If you look at that table and calculate the Min/Max values, you will see it is 100% consistent...there is a MINIMUM discharge current of 178.56W, and a MAX discharge current of 249.9W. This is likely because there are banks of resistors in there, and there are only so many they can "disconnect" from the discharge circuit on 2S. I was just very surprised to see the OP able to use a 5A discharge. If that is the case, then the table they show on their website and manual are incorrect/misleading. I did not buy the BD250 specifically because I wanted to be able to discharge at something less than 30A as a minimum. But if the website/manual are wrong, and anything from 0.01-35A can be selected for a 2S battery, I will definitely pickup one of these units. But since he was able to produce a chart that showed a 58 minute discharge time, then it means that 5A is really possible.

The table seems rather useless. If you calculate it, the 29.76V is exactly what you get on the full 8.4V of a LiPo with the max. 250W - given the same, constant max. discharge wattage (and that's what I think the table shows), current will rise with sinking voltage. I don't believe for one second that this is really the minimum discharge setting one can use - would the stupidest charger ever made.

I did some testing with my packs over on this thread with a 20A discharge:

https://www.rctech.net/forum/radio-e...e-lipos-4.html

I limited my test to around 2000mAh discharge since I don't have a discharge bank and was using regenerative charging to get the discharge current that high.

The BD250 is a pretty cool tool. The software will help mostly in keeping an eye on when their performance starts to degrade. Skyrc also has tool called the lipopal, which you can attach between the battery and the discharger. It keeps the batteries balanced as they discharge. It works like a balance board and more.

I don't make discharge graphs anymore since my newer charger comes with an IR meter, but I found the graphs very useful to give me information when performance was degrading on an aged pack, I created a 30A bulb discharger as shown here:
https://www.rcgroups.com/forums/show...0#post40308838

Good Luck!

The year isn’t 1995. You don’t use bulb dischargers on lipos. Period.

you can use any style of discharge 1 might have Ive used 1157 bulbs from my 1st lipo to todays.. a discharger is a discharger anyway you look at it.. just use fans to keep the heat under control (on the light bulbs)

I used halogen bulbs and they are a very cost effective method for discharging LiPo's (even to this day), though many folks are using resistor banks these days, in fact I currently use a resistor bank for cycling my packs for stock racing, though there is no difference between a bulb or resistor bank with regards to LiPo safety, you just need to make sure the draw is shut off at the appropriate voltage setting. I currently use an iCharger which adds all the safety features to make it very simple and safe, I only use resistors because they are a little smaller though they produce about the same amount of heat.

Absolute facts to support an absolute statement?

I think (or hope) he meant that you do not just directly connect a light bulb to the battery (like you could in the day of NiCd). Using it (or a resistor bank) in combination with a charger that supports this technique (like e.g. the iCharger) is of course perfectly ok and has nothing to do with 1995.

You risk pulling the voltage too low if you just connect lightbulbs to a pack.

You risk pulling the voltage too low if you just connect a resistor to a pack. Bulbs are just cheap readily available resistors.

You shouldn't be doing that either. You should only ever connect an actual active discharging circuit to a LiPo with LVC.