Idiot's guide to a self build battery

[Tinbum]

Thing is the hob keeps working and the really stupid thing is when it cuts the power to the oven it also shuts off a "cooling" fan so it takes longer to cool down. The "electronics" are just the clock/timer - so that is on my list to bypass as the timer doesn't work anyway.

I had a machine mart welder many many years ago that did that. I looked at rewiring it but, if I recall correctly, the fan was 110v and supplied via the main transformer. Always bought quality equipment from then on.

Tried for a price on assembled controllers (10) and it worked out about £10 each without the sdcard holder as that wasn't available. I'm guessing the MOSFETs can be replaced by using the relay contact to drive another contactor??

balance boards are about £2 each but a few parts are out of stock including the IC.

[Stinsy]

As cool as these super-fancy BMSs are, you only really need a balancer that shifts enough amps. The inverter takes care of charge voltage and low-voltage cutoff, and that’s all you need.

[openspaceman]

As cool as these super-fancy BMSs are, you only really need a balancer that shifts enough amps. The inverter takes care of charge voltage and low-voltage cutoff, and that’s all you need.

I'm glad you said that Stinsy as I was getting confused and concerned.

[Tinbum]

As cool as these super-fancy BMSs are, you only really need a balancer that shifts enough amps. The inverter takes care of charge voltage and low-voltage cutoff, and that’s all you need.

I'm glad you said that Stinsy as I was getting confused and concerned.

I strongly disagree. Your battery needs to tell the inverter what to do. The inverter won't reduce the current if the batteries are too cold or too hot, it won't shut down if a cell does go out of balance. It measures the voltage at the inverter not at the battery. I'm sure, if they could, battery manufactures would make batteries without a BMS.

A BMS has many safety features that are required.

[Swwils]

Good BMS vital.

[openspaceman]

I strongly disagree. Your battery needs to tell the inverter what to do. The inverter won't reduce the current if the batteries are too cold or too hot, it won't shut down if a cell does go out of balance. It measures the voltage at the inverter not at the battery. I'm sure, if they could, battery manufactures would make batteries without a BMS.

A BMS has many safety features that are required.

Oh well I shall have to learn much more before I delve into this. I knew a BMS was essential but thought simple voltage controlled charge discharge cut offs and cell balancing were the only needs.

[Tinbum]

Their are people that don't think a BMS is required and a lot more that think that you don't need communication between the battery and the Inverter. The latter is more debatable because a good BMS will protect a battery even without communication.

I would never run a Li Ion battey without a good BMS, they are not like Lead Acid where they will just boil away!

[Stinsy]

As cool as these super-fancy BMSs are, you only really need a balancer that shifts enough amps. The inverter takes care of charge voltage and low-voltage cutoff, and that’s all you need.

I'm glad you said that Stinsy as I was getting confused and concerned.

I strongly disagree. Your battery needs to tell the inverter what to do. The inverter won't reduce the current if the batteries are too cold or too hot, it won't shut down if a cell does go out of balance. It measures the voltage at the inverter not at the battery. I'm sure, if they could, battery manufactures would make batteries without a BMS.

A BMS has many safety features that are required.

This isn't as clear-cut as you present.

A cell won't go out of balance if you have a decent balancer. If you're trying to charge/discharge a small battery pack at very high power then temperature becomes important, but we're talking 14k or 28Wh battery packs being charged/discharged at 3.6 or 5kW, we're talking a C-rate pf 0.25 or lower, whereby temperature is largely irrelevant.

This isn't an e-bike with a teeny battery or a BEV charging/discharging at 100kW...

And don't forget these are LiFePO4 batteries not NMC...

[Tinbum]

You only have to look on forums to see how many people have been complaining of slow charge rates to see how the BMS has protected their battery.

[marshman]

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