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Sep 14, 2021, 11:57 PM
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K989 killing batteries?

A few days ago, my kids were driving my k989 around the living room and the car started acting weird (servo twitching and throttle worked intermittently). This is not the normal LVC behavior. I tried to charge the battery using one of those 1000ma usb chargers and it blinked red really fast and didnt charge. So i tried to charge a 2nd battery that came with the k989 and it did the same thing on the charger and on the car (not charge and twitching servo).

A little trouble shooting later, on both batteries the 1st cell read 0V (not a low number or OL, literally 0mV on my dmm) while the 2nd cell was 3.6 or 3.8V. I tried the usb charger with a different battery and it charged to 4.23V per cell and stopped so the charger appears fine. The car currently ran a battery down to 3.2V per cell and did the normal lvc behaviour. Since both the charger amd car seem to work right now, Im kinda stumped. And, since the k989 uses the balance plug for power, I have no idea how that circuit uses the batteries amd if they are discharging at the same rate. Does anyone had a similar experience with a k989 killing the first cell of 2s lipos? Anyone have a suggestion for troubleshooting this or preventing future batteries from dying in this car?

Thank you
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Sep 16, 2021, 04:53 AM
Low budget fun
Beaver_XT's Avatar
The stock 2-in-1 uses 2 pins of the plug. However I find that LVC is not entirely reliable as some battery may have 1 cell dropped more than the other. This is probably your case where one cell is not very good so it just went 0V.
Sep 17, 2021, 02:51 AM
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Hey thanks for responding! I could believe that the lvc doesnt catch one of the cells sometimes but its a bummer it happened to 2 batteries in 1 night.

Also, I find your videos very helpful! I wouldnt be shopping for more 1/28 cars if it wasnt for your videos. Im currently debating making an amr, amz, or k989 into a rwd drift car (not ready to drop the $$ on the drz yet). Your amz drift conversion seemed to work decent. Which path would you recommend?
Sep 18, 2021, 02:22 AM
Low budget fun
Beaver_XT's Avatar
AMR and AMZ are quite old now so don't expect to see all the upgrades or replacement parts to be available.
AMR will need some work to convert to RWD drift. I think it's should be easier than converting K989.
AMZ is nigh impossible to convert to RWD drift, however it's great as AWD drift and touring.

Personally I'd suggest you keep working on K989. If you do the electronics upgrade, providing you use the parts that are standard to 1/28 and not overdone by putting large motor in, you can move them to a better car in the future.
Keep it AWD first and once a diff is broken, turn it to RWD.

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