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Hi !
We have an small lead battery EV we want to put Mitsubishi miev 50AH Yuhasa cells into, the car has 6 x12v Lead cells for 72V pack at the moment.
There is so much solutions out there and some look good but are expencive.
Is there a DIY do it yourself kits that are not to much hassle or a china solution that works ? We are on a budget....Thanks
 

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Assuming the miev 50Ah Yuhasa is lithium-ion NMC, and the configuration is 20s1p, you will need in the least the following three:

1- 20s 45A balancer-protector $24 -
https://www.ebay.com/itm/72V-20S-45A-Lithium-ion-Li-ion-Li-Po-LiPo-Polymer-Battery-BMS-PCB-System-Balance/112359990041?hash=item1a292d6319:g:ZxEAAOSwXXxZXNut

2- step-up CCCV 900W charger $20 -
https://www.ebay.com/itm/DC-DC-BST900W-CNC-Boost-Converter-8-60V-Step-up-10-120V-Solar-Charging-CVCC-New/401320880903?hash=item5d7096ab07:g:EUoAAOSwhvFZC5Li

3- power supply - 36V or 48V, about $30.

You may be able to put more than one of these in parallel to get a bigger punch.
 

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Thanks a lot solarsail for the suggestions. Do you have experiance with this products? We have 40 cells so 2 in parallel and 20 in series , but the packs are packed in 8x3.7volts so I dont know if I should repack to have 2 and 2 in paralell or 8 and 8 in paralell...
 

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I am building a 14s (14 in series) for 48V, so I am using a 14s balancer. But I am using the same charger. See
http://www.diyelectriccar.com/forums/showthread.php/18650-13s10p-project-48v-x-34ah-188618.html

I am not sure exactly what you are saying. But if you want to get 72 volts, you need to wire them 20s2p. Make sure the BMS (balancer protector) can deliver the amperes you want. If 45A is not enough, I found a 90A BMS board on eBay, that you should use instead.

It must be 2 in parallel then series with the next two (in parallel), then series with next two, etc. If you are not sure about something as fundamental as this, then I would advise that you not proceed, but get help from an electronics person. You would not be able to connect the BMS and the charger, or program the charger. You are dealing with a lot of power, about 7.2 kWh, which is serious. You can easily destroy cells, cause fire, or worse, injure yourself. If any cell voltage drops below 2.0V, it is most likely destroyed.

As explained above, 20s2p means you first wire 2 cells in parallel. So now you have 20 cell-pairs, each 3.6V. Then you wire these 20 pairs in series to get 20x3.6 = 72V. Note that when 100% charged, the pack will be 20 x 4.2 = 84V. Hope your EV can handle this. It can be discharged to as low as 20 x 3.0 = 60V. When wiring two cells in parallel, they have to be equal in voltage before you do that. First connect a 0.5 ohm resistor between the two positives, and wait for a while for it to equalize before soldering permanently.

You can also wire 2p20s but is not advised unless you want to get 180A out using two 90A BMS.
 

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All of these things could be weather proofed and put on a motorcycle.

I'm not sure about the 120v AC to 36v-48v DC... Is there a good psu for mounting on a bike so that you could pig it in anywhere?

I'm the guy that drives till the needle is WELL below the "E" ;)
 

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@espen

do you want a fully automatic BMS that controls everything, or do you just need a cell monitoring type BMS that reports status such as cell voltage and current, and puts you in control to decide when to shut down due to overvoltage, undervoltage, overcurrent, etc?

i have been working to reverse engineer the CMU board on the mitsubishi cell modules, but it communicates over a CAN buss and is very complicated to break the codes. Those boards provide a very low level of cell balancing of about 0.1 Amps thru bleed resistors, but they primarily report cell voltage and temperature to the main BMS unit which controls charging. They also have cell-level fuses which would open in the event of an over-current condition. There is another box, the EV-ECU, which controls the pack discharge current. The whole system is very complicated in order to control everything, such as would be expected by an OEM.

For diy you can do with less automation if you are willing to make the decisions. i would recommend to use a cell monitoring approach to measure cell voltage and temperature and pack current, and control the pack operation with large contactors on + and - , rather than switching a multitude of tiny FETs.

What is the maximum current that you think you would need or desire? That would help determine what sort of switching device you need.

Where did you purchase the cells--i would like to buy some for testing.
 
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