Battery Build

[sling]

I'm building a battery pack for my 2005 YZ125 EMX build. I have an electro and co kit with QS-138 70H and EM-260S controller on the way. The plan is 20s15p (75Ah) using 300 Samsung 50s 21700 cells. I was curious what you thought of a DALY BMS (and is an active balancer worth it?) and putting it outside of the battery pack?

Thanks!

 

[Bob Casper]

Outside of battery is the direction I will be trying. Daly will be the BMS too

 

[sling]

is it safe to bypass the BMS during discharge?

 

[Philip]

is it safe to bypass the BMS during discharge?

That's what @DonCox does.

I am thinking, without more sophisticated electronics than a simple BMS, it is safer to let the battery drain low and feel the gradual reduction of power rather than let the BMS kill your bike completely (or partially in case of multiple BMS/batteries).

A typical BMS would also kill your bike in case of an over-current. Like, when you need the power the most.

 

[sling]

That's what @DonCox does.

I am thinking, without more sophisticated electronics than a simple BMS, it is safer to let the battery drain low and feel the gradual reduction of power rather than let the BMS kill your bike completely (or partially in case of multiple BMS/batteries).

A typical BMS would also kill your bike in case of an over-current. Like, when you need the power the most.

It seems to me the BMS bypass is a way to cheap out on a more expensive BMS. (the difference between a DALY 30A and 500A is 270$). All the professional brands have a BMS with high enough discharge capability.

By bypassing you lose the ability to monitor cell voltages and temps. Assuming the EM-260s will pull its set amperage and nothing more (350a out of the box from e&c).

I'm curious how consistent cell voltages will be throughout the pack after an hour of very high discharge riding. I'm assuming there will be some change, but enough to reduce the life of the battery pack significantly? Would a BMS with a 1A active balancer even make a dent in this? Maybe the voltage gradient throughout the pack has more to do with pack construction (non-uniform heat generation from resistivity differences)?

 

[Philip]

Yes, for the DIY market cost is also a big factor.

By bypassing you lose the ability to monitor cell voltages and temps

That's not necessarily true. You can keep the BMS hooked up to the battery at all times but use it for charging only. This way you will retain all the battery monitoring and balancing.

In fact, you can have the BMS power not the motor but just a simple light bulb, or a light bulb relay. If the BMS cuts out due to a low voltage or a high temperature, the light bulb, or the relay, will turn off. The light bulb turns off or on, and you know it is time to go home.

 

[sling]

In fact, you can have the BMS power not the motor but just a simple light bulb, or a light bulb relay. If the BMS cuts out due to a low voltage or a high temperature, the light bulb, or the relay, will turn off. The light bulb turns off or on, and you know it is time to go home.

wow. This is a great idea! it's possible it could also be wired into a contactor to cut power from the pack without spending so much on a more expensive BMS.

 

[DonCox]

We run most of our batteries with the BMS used only for Charge control. The discharge low voltage control is done with the Controller. I use the Votol controllers, and the have a Soft Undervoltage setting (which I set on my 20S12P battery at 65V), it slows the motor way down but still runs, and a Undervoltage setting set at 59V which turns the motor off. While charging you can monitor all your setting and all the cell group voltages. They are usually within .05volts or less of each other. We also put the BMS outside of the battery box so it doesn't add heat or get heated up by the battery. I have only lost a few cells over the years, probable about 20 batteries. I have been using the ANT Smart BMS, but they seem to be more sensitve to failing, being not waterproof, etc. So I have started using the Daly Smart BMS's. The phone App is better on the Daly, IMO.

 

[DonCox]

I'm building a battery pack for my 2005 YZ125 EMX build. I have an electro and co kit with QS-138 70H and EM-260S controller on the way. The plan is 20s15p (75Ah) using 300 Samsung 50s 21700 cells. I was curious what you thought of a DALY BMS (and is an active balancer worth it?) and putting it outside of the battery pack?

Thanks!

Have you looked at the Molicel P42A cells. I get right at 40A out of each cell. I can test them by watching my max current on one side of my battery or the other side. I have 2 20S6P batteries in my 2014 YZ250F. I can select one or the other, and or both, and I can see about 240A out of either side. ( about 40A per cell) but a solid 400A on both, controller limited. They have been very reliable and cost effective. I don't run n Active balancer. I mentioned why I put the BMS's outside the battery in the previous post.

 

[Jim Beagle]

We run most of our batteries with the BMS used only for Charge control. The discharge low voltage control is done with the Controller. I use the Votol controllers, and the have a Soft Undervoltage setting (which I set on my 20S12P battery at 65V), it slows the motor way down but still runs, and a Undervoltage setting set at 59V which turns the motor off. While charging you can monitor all your setting and all the cell group voltages. They are usually within .05volts or less of each other. We also put the BMS outside of the battery box so it doesn't add heat or get heated up by the battery. I have only lost a few cells over the years, probable about 20 batteries. I have been using the ANT Smart BMS, but they seem to be more sensitve to failing, being not waterproof, etc. So I have started using the Daly Smart BMS's. The phone App is better on the Daly, IMO.

Hello Don, great info there...
Which specific Daly model are you using ? Thx. Jim

 

[DonCox]

Here is the Aliexpress link. I use this size since we only use it for charging.

I use the 20S version, 80A

https://www.aliexpress.us/item/3256805881158602.html