Budget 90ah 48v lifepo4 battery build (under a grand)

[Volt_Ampere]

Any balancer will have active devices (FET's usually) that connect the load to the cell to be balanced. An active balancer is more complicated because it has to route the current from the higher to lower voltage cells.

[augiedoggy]

Originally Posted by Volt_Ampere

Any balancer will have active devices (FET's usually) that connect the load to the cell to be balanced. An active balancer is more complicated because it has to route the current from the higher to lower voltage cells.

True.. at some point though I have to rely on the tech.. I already went with 16cells vs 32 and a mechaniacl relay bms for added reliability.

[Volt_Ampere]

I prefer a mechanical relay for the BMS main control. Solid state at the high amps is a source of heat. I even use a relay for charger interrupt on my setup. (an automotive 30 amp relay)

[DaveTM]

Originally Posted by Volt_Ampere

I prefer a mechanical relay for the BMS main control. Solid state at the high amps is a source of heat. I even use a relay for charger interrupt on my setup. (an automotive 30 amp relay)

Yeah---^^^^---This

[jasonojordan]

Is there an ideal amperage you should be looking for with the active balancing?

[Volt_Ampere]

Here is the issue: When active (or passive) balancing, you get a voltage drop in the sense wires that measure the cell voltages. As long as your balancer doesn't measure the voltage during balancing (when the current is on) you can have a reasonably high current (a couple amps). Most passive balancers limit the current to under an amp because of the heat generated. Active balancers can balance with higher currents because they are much more efficient and don't generate much heat. My balancer does NOT measure battery voltage when the balance current is on. It turns it off for a couple seconds every 10 seconds to measure battery voltages. That way, the thin sense wires don't mess up the voltage readings.

[Pat911]

To mitigate the risk of the active balancer failing and damaging cells, you can simply unplug it when not required. It’s just two plugs. Wires can be left in place and the balancer can be stored under the seat so it’s not misplaced. It’s not needed often but when it’s needed just lift the seat and plug it in.

[augiedoggy]

Well the point behind the power switch which turns the active balancer on and off was so I could leave it off and just turn it one when needed.. They designed it with this provision for a switch so I think im going to take the risk. plugging it in and unplugging it is going to be a bit awkward when installed in my cart.

I agree on the mechanical relay vs the mosfets.. Mosfets or even solid state relays under high load generate a lot of heat, which was what I was getting at the other day when comparing making 500amps of motor current from 200amps from the battery vs with 300amps.. Theres always a tradeoff somewhere. Ive had enough car audio amp and solid state lamp ballast failures over the years to tell me this and its why im trying to make the beefiest battery current wise that I can on the budget I have.

[Pat911]

You know your installation better than anyone else Augiedoggy so do you’re best placed to make the call on the balancer.

As for the mosfets vs solenoid argument, I prefer mosfets as if they’re rated correctly then they should perform well. Arcing can be problematic with relays/solenoids. I use an 80A BMS on my cart, but I don’t pass motor current through the BMS. I use the BMS to to cut the key switch under a fault condition. This effectively disconnects the load. The most current that passes through the BMS is the charge current, which is 33A.

[augiedoggy]

The bms I went with does have a resistor which allows a low amount of charging current even when the relay is open and it prevents arching when activating it. I have no reservations about using mosfet bms for lower current applications. I mean I am using them for my active balancer that you guys are telling me I should unplug in case those same mosfets fail?
The original Mosfet style 500 amp 240 amp continuous ANT BMS I bought originally to use is what extreme team used in some of their packs and based upon the complaints here I am glad I chose not to use it.
Time will tell if I made the right call because I know there are drawbacks to the BMS I chose to use as well