Help with cell monitoring and balancing

[bestkeptsecret]

Hi there.

I'm looking to build a mod with 6 cells in parallel. Looking for some help with monitoring and balancing circuitry.

Anyone got any ideas / reference material?

 

[dc99]

I must be missing something, why do you need balancing if they are all in parallel? I asume its a mech mod

 

[bestkeptsecret]

I must be missing something, why do you need balancing if they are all in parallel? I asume its a mech mod

I'm thinking of it as a hybrid mod so as not to offend the more vociferous mech heads.

I'm looking to include a charging circuit so on the basis there are 6 cells what I think I need to do is make sure there is no initial surge that could damage the cells, that none get hit with more current than they should individually or collectively, and ensure cut off occurs at 4.2V

 

[dc99]

I'm thinking of it as a hybrid mod so as not to offend the more vociferous mech heads.

I'm looking to include a charging circuit so on the basis there are 6 cells what I think I need to do is make sure there is no initial surge that could damage the cells, that none get hit with more current than they should individually or collectively, and ensure cut off occurs at 4.2V

Most of the onboard chargers are 1A so it would take forever to charge six batteries. Im not aware of a balance charger for 1S batteries. Which is what you will have. May I ask, why 6?

 

[bestkeptsecret]

Most of the onboard chargers are 1A so it would take forever to charge six batteries. I'm not aware of a balance charger for 1S batteries. Which is what you will have. May I ask, why 6?

Of course you may. I'm looking for thoughts and opinions as well as help as part of refining my ideas. Discussing thoughts and ideas and testing them with others is why I'm here

The reason I was looking at 6 is that with that number of I can plump for high capacity low draw cells and put such a low load on each as a % of their Acont rating that it will maximise the usable capacity available from them.

By putting less stress on each cell I would also be able to minimise Vsag and Vdrop thereby getting the most out of a non series setup.

Rather than 6 3500mAh 10A 18650's I'm also toying with going for 4 5500mAh 20A 26650's.

On the charging circuit. Yes balancing was a poor choice of words on my part. What I'm really needing to put in place is surge protection and ensuring that no cell can get hit with more than 0.5C. Also I don't want any possibility of overcharging so I want to make sure charging cuts off when the cells hit 4.2V. It doesn't really matter whats out there btw. I'm not looking for off the shelf boards. I will build what I need.

 

[dc99]

In that case I might go for 4-21700's. I understand now what you are after. Enough to not stress the batteries and not have a big V sag. Wouldnt it be nice if someone built a 1S lipo with high capacity. As far as monitoring and charging this would be past my pay grade. There are a couple of guys that come on here every now and then that can probably help though. David4500 and Dave from "breaktru". There not on here a lot but you could message them

 

[bestkeptsecret]

In that case I might go for 4-21700's. I understand now what you are after. Enough to not stress the batteries and not have a big V sag. Wouldnt it be nice if someone built a 1S lipo with high capacity. As far as monitoring and charging this would be past my pay grade. There are a couple of guys that come on here every now and then that can probably help though. David4500 and Dave from "breaktru". There not on here a lot but you could message them

I think you might be right and I am starting to lean that way. Though I really like the look of the 26650 5500mAh 20A ShockLi cells, particularly having seen the Mooch discharge graphs, I can't find them in the UK. The rest of the cells in that class don't really seem to offer enough performance over 186/207/217's to justify the extra real estate they need.

With batteries we are always going to want more than they can deliver for the foreseeable future I reckon. I don't think you can get around the basic principle that more capacity requires more density, more density means more resistance and a lower current rating. I guess at some point LiPo's and Li-ion's will give way to a new type of cell, but even if they give us around 10,000mAh at 10A, 8,000 at 20A etc in a 18650 package we will still be hankering for more more more.

Thanks for the tip might see if I can tap them up once I've collected my thoughts and made up my mind which way to go.