Help for BMS wiring and BMS cutoff limits needed

ESK8 Electronics
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Summary

I have started to buy the parts I need for my first build. Next up is buying battery and BMS and weld it together. I have drawn a wiring schema that you can see below. Parts:

Battery

LG HG2 Lion battery. Based on some reading this battery should do the job. Hard to find stores who sell good batteries in Norway, but these I found (even though quite expensive). Data sheet: http://keeppower.com.ua/download/2015-06/datasheet-LG_INR18650HG2-1.pdf

From what I read of the battery is “emtpty” when the voltage goes down to 2.5V and it should not charge above 4.29V.

The BMS

I have looked at the Bestech http://bestechpower.com/37v10spcmbmspcbforli-ionli-polymerbatterypack/PCM-D223V1.html. There are several people stating they use these boards with integrated switches. So I emailed Lucy at Bestech and asked how the recommended to set the parameters for LG HG2 batteries in a 10s3p configuration.

What settings would you recommend?

I recommend over charge detection voltage in 4.25V+/0.05V Over discharge detection voltage 2.50V+/0.0625V Please check whether it is suitable for your project or not.

  1. Based on the battery data sheet I would say that the over charge detection voltage should be set lower, to 4.2V. However, should I also have some margins? I.e. setting this parameter to e.g. 4.15V?

  2. Over discharge is set to the bare minimum according to the battery data sheet. Should I have some margins on this parameter? E.g. set it to 2.7V?

  3. Is release voltage ok to have 0.2 V from the detection voltage? I.e. Over charge release voltage at 4.05V and Over discharge release voltage at 2.7V?

Wiring and switch

esk8 drawing-3.png960Ă—720 34.1 KB

Two drawings - one with an X90s anti spark to be able to break the loop and the other without. Does this wiring look sane? :thinking:

  1. I guess I could do without the X90s or is it needed to disconnect the VESC while charging? According the Bestech BMS information the BMS Switch must be ON while charging! That means that the VESC do have power while charging. As long as the BMS is doing things right I guess that should be ok?

Thanks for any feedback on the wiring, BMS choice, switches and all other!

Edit: Changed the wiring.

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Think there is something wrong.

There should be a P- that will go to the - of the VESC. And the C- is for the charge port.

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Yes - you are correct, @mptrs! I updated the wiring schema. Thanks :slight_smile:

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Does anyone have any experience with LG HG2 and BMS settings? Over charge detection and over discharge settings are preconfigurable on the Bestech BMS.

And - what happens with regenerative power while breaking - will it function with a BMS between the VESC and the battery?

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No problem, happy I could help. I’m in the middle of all this right now as well.

For your other question, maybe @Namasaki can help out. He knows allow about BMS, wiring etc.

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The regenitive charging does work with the Bestech bms and it prevents over charging from regenitive brakes.

Some of the parameters of the Bestech bms are adjustable at the factory and can be specified during the order process.

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@Namasaki thank you!

I think I will follow the white paper and set the over charge detection voltage to 42V. The over discharge I will set to 25V.

For more control during use I can use the cut off on the VESC for discharge. I will buy a charger that goes to 41V: http://www.groetech.de/index.php?main_page=product_info&products_id=837

This way I will stay clear of the upper and lower voltage limits of the battery.

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I agree w this but make sure that the charger you use doesn’t contraindicate the over-charge detection threshold you’ve chosen… if the charger is charging to 4.2V but your BMS cuts off at 4.15V that wouldn’t be good…

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Good point! So maybe 4.25V over charge is ok. I will keep the settings as Bestech recommended with 4.25 Volts over charge and 2.5 Volts discharge.

1 Like
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Hey, I tried to buy BMS from the website following that link that you shared but it seems like there is no option to buy. Can you suggest me how does it work? BMS is the only thing that holds be to finish my longboard. thanks mate

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I communicated with Lucy at [email protected]. Hope she is real because I ordered two! :slight_smile: I can give you a heads up if I ever get the BMSes :wink:

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@tonystark I just received the BMSes! So you can contact Lucy and order through her.

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Hey, sorry to necro this but I noticed that your schematic with the loop key is connected to the positive wire. This is fine if you’re wiring it to the female connector but if you’re using a male you should connect it to the ground wire instead to prevent damage/injury if you or someone accidentally touches the exposed parts of the male connector.

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Hello, can you post a build picture of your final product?

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Had anybody adjusted any factory parameters in the comfort ood their own home? Or is it kinda like once those settings are set that’s it?

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IMG_5825.JPG4032Ă—3024 1.66 MB

Can you please look over my design? Did I get it right?

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The parameters are factory set. You have to request them when ordering the bms. This is the case with Bestech

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Ok thanks @Namasaki.

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@TunaTee
Before you dive in to building an electric skateboard, you should do some fundamental research on the basics of electronics. Not having an understanding of these basics can have a serious effect on the overall performance of your board. To answer your questions:

  1. The voltage meter (voltmeter) sits across your positive and negative wires. In your case, the voltmeters positive wire should connect in parallel to the positive wire of your battery 1, and the negative wire of your voltmeter should connect in parallel to your negative wire of your battery 3.
  2. I dont know what you’re after here
  3. Yes, the thickness of the wire has an extreme effect of the flow of electricity. If you have a 1mm wire with 80A of current flowing through it, it will melt the wire. I recommend checking what amount of current you will have flowing through the wire and then buy wire that is rated at that voltage and amperage. Hope this helps Matt