Need a BMS fast

[john61ct]

Yes BMS is just a collection of functionalities.

If more than minimal balancing is required, better to do with other devices, and not necessarily at high SoC%

If you top balance, then LVC should either be based on the first cell/group to hit your setpoint

or if you use pack level voltage it must be more conservative (higher) than using cell voltage.

If you bottom balance, then charging should be terminated based on the first cell/group to hit your setpoint

or if you use pack level voltage it must be more conservative (lower) than using cell voltage.

All three of these functions can be done without "a BMS" as such.

Temperature based protection

and over current protection are very often separate.

Obviously a $25 BMS is very different from one costing thousands as with EVs.

[Rucker]

Originally Posted by kazetsukai

+1. They can be used on their own (which can only see the pack voltage) or in conjunction with the Electrodacus (which can see pack and cell voltage).

In terms of wiring the VBP only allows for one-way current (you can't charge and discharge through them- only one or the other). So e.g. you need to place the BP just upstream of something like a DC fuse block, but downstream of a common bus bar where your charge sources are connected.

Multiple VBPs can be used to create a tiered system for DC appliances- cutting out superficial stuff earlier on to keep critical loads going longer, which will restore in reverse order as energy becomes available. You'd put one VBP for one DC fuse block and another for a different fuse block, set one to a higher voltage cutoff. An example would be a DC charge port used specifically for a CPAP or something similar.

My discharge strategy is to have the inverter cut out at 20% SoC, most DC appliances at 10-15%, then whole system shutoff at 5%.

Even the largest VBPs are not suitable for use with inverters, do not put inverter loads on them.

First time I've heard of these. They sound like what is used on the Star Trek Enterprise:
'Systems are failing. Navigation offline; shields at 35% power.
'Divert power from the blasters then!'
'No cannae do-the VBP only allows power in one direction.'

[kazetsukai]

Originally Posted by Rucker

Apparently the Daly does a terrible job of cell balancing so I bought a cool little capacitor-based active balancer for thirty bucks that seems to do a fantastic job (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1).

I think the problem with the DALY for balancing is that it does balance only at a very high voltage, when many of us want to charge conservatively- I for one don't want to charge much higher than 3.5V, which I believe is under the start balance voltage.


I think the smart BMS allows you to program balance voltage, I'll see one way or another as I'm going to do a lot of custom integration with mine. Balancers should be relatively idle most of the time for very new battery banks, cool link though.

[Rucker]

Originally Posted by kazetsukai

I think the problem with the DALY for balancing is that it does balance only at a very high voltage, when many of us want to charge conservatively- I for one don't want to charge much higher than 3.5V, which I believe is under the start balance voltage.


I think the smart BMS allows you to program balance voltage, I'll see one way or another as I'm going to do a lot of custom integration with mine. Balancers should be relatively idle most of the time for very new battery banks, cool link though.

Can't wait to get the new one and learn how to use it.

I'm hoping between the Renogy Charge Controller and the BMS I can set up a couple of modes of charging:
-Full/Max, for heavy usage;
-Weekender, for medium usage;
-Idle, where the cells sit at half charge pretty much, but occasionally take on charge as they drift down.

The active cell balancer on my battery is operating quite well but my cells are all at 3.5+; I'm going to let them ride down and see whether the device continues to balance all the way down to half charge or so.