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hygy

fimi x8 se battery connector / dual car charger

by hygy May 30, 2019
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Hi, I just wanted to tell you that I did some tests on the Fimi battery and original charger, and the original charger is actually current limited to 3 A. If allowed, the battery will draw significantly more than this (yes, I tested), so I would be cautious about your setup here, since the charger you have will allow more than 4 A to each battery, and it has a supply voltage to support that.

In other words, you will charge the Fimi batteries at a higher rate than the original charger, and while it may be fine to do so, I think you will possibly also degrade the service life of the battery.

Thanks for your note. Til now I charged many times with this (on real usage on a motorbike in a tankbag), meanwhile travelling from one place to the other. I watched regularly how hot is it and its cold (there were really hot outside), and it stays cold. (And the charging time is about the same as the factory charger.)

The other thing is that the most basic LIPO batteryes can be charged safely with 1C. Thees batteries are 4500mAh so theoretically it can be charged with 4.5A. (Latest developed batteryes can be charged with 2-3C.)

And what I see with other lipo batteries if I enable the charger 5A it does not charge with it. Now I started to charge a 2200mAh 4S battery started from 4V and it is draws 3.1A now (it can draw 5A if the charger wants), so I think the charger controls the amperage. (The lipos first charged with amperage, then with voltage.)

What could have happened that the carger circiut in the fimi battery cannot handle the max 4A charging amperage, but after the first test it stays really cool so it can handle whatever amper it is using.

Bu feel free to change the adapter to any other supply that can output max 3A at 13.05V. The connector what I created stays the same. :)

You are probably OK, then. I just wanted to let you know that the original charger limits the current to 3A, while yours (at least in the specifications) will supply 4.1 A to each battery. Did you ever measure the actual current going to the battery?

As for the connector, I actually designed my own, which doesn't use a PCB for the pins like yours. Mine has the pins directly mounted in the plastic, so it is very tricky to solder (need to be very quick and have a high-wattage soldering iron). I also didn't have any suitable pins, so I made my own pins from a sheet of thin copper that I folded once to get to the required thickness. I haven't published mine, because for most people I think yours is easier to make, provided you can find somewhere to buy the pins. You didn't provide a link for where to buy those, so maybe you can add that?

As a final note, I am going to just use a laptop power supply (19-20 V) and a step-down buck converter (those are dirt cheap and work well) with current limiting to charge the battery. As long as the power supply has enough oomph (mine is 95 W), I can connect two step-down converters to it, and charge two batteries simultaneously (just like your setup).

So I attached a screenshot about the power consuption.

So it was 14V and 1.59A (the battery has 3 leds lighting) so its using 22.26W for charging (-the power loss in the supply).

The original supply maximum consuption is: 13.05V*3A=39.12W so I think the charger included in the battery regulates the charging current.

Now I cannot test it with an empty battery, couse my X8 sent back to repair to Fimi, but I think again this whole thing is working good.

I don't think the battery limits the charging current, as that would create way too much heat without having a super efficient switching power supply built into the battery. However, it does monitor the current, and if the current is too high (and quite a bit more than 3 A), I think it will stop the charging. I haven't really tested that properly, but I think I saw it happen when I created my own chargers and had the current limiter on the charger set too high.