On The Bench | Youme Batteries
Your usual Lipo supplier done a bunk? Here’s a solid alternative.
Now that the big, Hong Kong-based online hobby retailer (you know which one!) has seemingly left the UK and Europe we have to look elsewhere for our LiPo batteries. I like to buy from UK suppliers whenever I can but the prices they charge for LiPos are often eye-watering. Quality can be a problem too. I bought some batteries from a reliable source a year or so ago that turned out useless. They had internal resistances (IR) starting at 35mΩ, falling very little after three charges. They went back. So my message is take care when buying an unknown brand. Ask around, but if you get no joy buy one and test it out as I have done below before committing a lot of money.
I covered IR in a previous article (link in Resources below). However, briefly, a battery is made of metals and chemicals that have electrical resistance, internal to the battery. This takes energy from the current, warms the battery, and drops the voltage. Ideal values are between 1 and 4 milliohms (mΩ). Up to 10 is fine. The value goes down over the first few charge and recharge cycles, or should.
A mate at the club called Mark regularly flies impressive ducted fan models that need efficient batteries. He turned up with some Youme batteries that he had just bought, a name that was new to me. I decided to buy a couple of them to replace some Zippys that turned out to be duds when I dragged them out for my old WOT Trainer I wanted to use for buddying. It turned out they were six years old. I got two Youme 4.5Ah 4S batteries from a supplier on eBay for £45 for the two, very much a competitive price.
They are very solid and well made. I especially liked the balance plug. Surprisingly they are about 15g lighter than the old Zippy batteries and the same size. Mine came with EC5 connectors but I decided not to change them to XT90s until I was sure I wouldn’t want to send them back. I soldered on the XT90s once convinced all was well. You will need a very powerful soldering iron. Even my 175W electric gun wouldn’t have coped. Some time ago Mark suggested a gas (not gasoline!) powered soldering iron. I bought one and now use nothing else on large gauge wires and big connectors. There is no temperature control so you have to take some care not to keep it running between joints. Wonderful bit of kit.
I measured the IR as delivered, then again after a full charge. I then discharged to storage and did a second full charge. Results below. Being good I then discharged them to storage again after looking at the rotten weather forecast. I will of course check again after a few more charge cycles.
So these results indicate batteries that are not equal to the very best Turnigy nano-tech ones, which have as low as 1mΩ , but are perfectly good. The batteries were marked with a rating of 60C but that is absurd. At 4.5Ah that means a maximum current of 270A. At that current the 27mΩ would drop the battery by 7.3V. A more normal 50A would give a 1.35V drop so I would rate the batteries as 15C or 20C. I reckon you need resistances of around 2 on average to rate at 60. If Mark had telemetry it would be interesting to see what drop he got from his ducted fan currents. He has now tried the batteries in a propellor-driven large scale model and estimates 10% more speed.
ProTip: Recovering Dead LiPos
Another hint from clubmate Mark: if a LiPo has been allowed to discharge very fully, for example by being left hooked up for a day, a charger might not recognise that it is there and will refuse to charge it. One trick is to make the charger think it’s not a LiPo. For example charge it as a NiMH for a while. Once it has some voltage in it the charger might then charge it as a LiPo. No guarantee though and be cautious with the charging and the first flight test.
Following an idea from my mate Keith I wondered if the IR, or at least the differences, are one reason why some batteries last longer than others. Perhaps the ones that last the longest are the ones where all IRs start much the same. A higher value cell would waste more energy and heat up and degrade more so perhaps creating a vicious circle (not cycle!).
The acid test? I’ll be buying some more when I need to. Unfortunately at present Youme do not do a full range of sizes. There is no 2.2Ah 3S for example.
©2023 Peter Scott
Resources
- Youme Power — The ‘official store’ on AliExpress.
- Electricity for Model Flyers | Part II: Internal Resistance and Why It’s Important by the author. — “You will see the voltage drop. But why? The stuff that the battery is made from has resistance, called ‘internal resistance’…”
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