amirsh34 Posted August 16, 2020 Share Posted August 16, 2020 i have bought a military battery at a yard sale and i want to use it as a backup battery for my uni, i have successfully discharged from it using the positive and negative holes but i cant seem to charge it using the same method can anyone try to help me? thanks the positive is the upper hole and the ground is the bottom hole, does anyone know whats the hole next to the negative is for? Quote Link to comment Share on other sites More sharing options...
Philip W Posted August 16, 2020 Share Posted August 16, 2020 Probably you need to find out what kind of rechargeable battery this one is. Lead-acid, NIMH, or Lithium-Ion? They use different kind of chargers. For Lithum-Ion batteries, they usually have a BMS board to protect the battery from voltage going too low. So if you discharge it, it should suddenly lose the power. If that's a Lead-Acid, it should be keep pumping out voltage until the last drop. I am not familiar with NIMH, maybe someone else here can clarify it for us? Quote Link to comment Share on other sites More sharing options...
amirsh34 Posted August 16, 2020 Author Share Posted August 16, 2020 Its definitely a lithium ion, and it had a sticker that said this: Discharge: Max. voltage 16.8V Nom. voltage 14.8V Min. voltage 10.5V Charge method (CCCV): Charge voltage: 16.8VDC max. Recommended charge current: 5A max so i tried just plugging a dc 12v charger to the positive and negative and it didn't worked. maybe it has to do with the middle hole Quote Link to comment Share on other sites More sharing options...
redsnapper Posted August 16, 2020 Share Posted August 16, 2020 unless u know the specs of this batt (v,i) u shld not connect it to ur euc. proceed with caution when trying to connect external batt to mboard etc as u can kill ur existing batt and or the mboard. see the forum for examples of battery mods etc if u r not already very skilled in this kind of mod... Quote Link to comment Share on other sites More sharing options...
meepmeepmayer Posted August 16, 2020 Share Posted August 16, 2020 Whatever voltage your wheel has, it's going to be much higher than this battery. So you can't charge your wheel directly from it. You'd need a converter to increase the voltage (don't ask me for details about any electronics, I know nothing there). Quote Link to comment Share on other sites More sharing options...
Philip W Posted August 17, 2020 Share Posted August 17, 2020 (edited) Good, now we have the info to know what kind of battery this is. Since its max voltage is 16.8v, it should be many combos of 4x3.7v batteries connected in parallel. 4 hours ago, amirsh34 said: so i tried just plugging a dc 12v charger to the positive and negative and it didn't worked. maybe it has to do with the middle hole I think it's probably the case. For that many parallels of combos, the discharging could be quite dangerous. Even the charging can be 5A, probably the discharge will be 30A and above. So naturally they separate the charging and discharging port. In your case, the top hole should be the discharging port, and the lower(middle) hole is the charging port. You will not detect a voltage difference between the middle and the ground port(lower one) because there are diodes in the charging port to prevent the wrong way of charging. Diodes will cut down 1 to 2v of voltage, so when you apply the 12v voltage to the middle and lower port, basically you are applying 10v to the battery. For the battery itself has minimum volt of 10.5v, Of course you cannot charge it. You need a good 16.8v constant-volt-constant-current charger to do the job. Something like this: https://www.amazon.com/dp/B07T244GYV This is a 2A charger, it will take longer to charge, but it should do the job. Just be careful for the discharging port (top). Even though it's low voltage, with such high current discharge, that thing can do you a lot of damage. In order to use this to charge regular EUC (67v), you need a boost converter like this: https://www.amazon.com/dp/B08B63RYD6 It can convert your military battery 16v to EUC's 60v and charge your EUC battery. Again, just be careful with the discharging current. Also, since 16v to 60v is a lot of difference in voltage, expect a 70%-80% efficiency, instead of 95% it advertises. Now here is my disclaimer: I don't claim any responsibility for giving you this article. All of the above is purely bullcrap. You do those things at your own risk. Edited August 17, 2020 by Philip W 1 Quote Link to comment Share on other sites More sharing options...
Chriull Posted August 17, 2020 Share Posted August 17, 2020 10 hours ago, amirsh34 said: so i tried just plugging a dc 12v charger to the positive and negative and it didn't worked. That's not the best idea! You measured the output voltage before? This 12V charger is a lithium ion charger? Are the li ion cells still in good condition? So first thing to check should be the output voltage! 6 hours ago, Philip W said: EUC's 60v 67.2V and for some wheels with input protection at the BMS some tenth of volts more. ... If one has a dmm that not only shows the tenth of volts, but also is precise enough... Depending of course on the wheel one has - could be 84V or 100.8V, too... And the Ah/Wh of the pack would be interesting - if it makes any sense as backup battery or is just a drop in the ocean... Quote Link to comment Share on other sites More sharing options...
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