Voltage display

Is there a product out there that can display all of the cell voltages on a single display for a 20s lipo pack, I am sure I have seen one with a bar graph display which lets you see the cell balance at a glance. The other option is 4 cell logs so each can display 5 voltages, I know I could do it with 3 but with 4 I would have quickly comparable totals for each display.
If i could achieve this with 1 display I might put it on the bike, if I have to use cell logs I will build them onto the charger which will also house the off bike BMS so I can see the balance and health of the discharged pack prior to charging and or balancing. My charger is a Cellman switched type so I can choose between 90% bulk charge or 100% balance charge as the BMS will only kick in if any cells hit 4.2v.
The charger will connect via a 25 pin D-sub with 3 pins each used for + and - and 19 intermediate cell monitoring connections.

Plug and play 20s bulk or balance charger

I think it's the Adapto controller system you have seen.

http://endless-sphere.com/forums/viewtopic.php?f=6&t=36375&p=845325#p843723

Must be young if you think you can ride, and read a cellog at the same time. Couldn't do that with my eyes. I can see my CA display fine but have to really squint to see a cellog.

If you must stop to read it, you can just carry one cellog in your pocket, like I do. Just have an easy access to your jst plugs.

If you have built your pack properly, and removed all the packs with a shitty cell, WHY DO YOU NEED TO WATCH EVERY CELL DURING THE WHOLE RIDE?

Are you running them off the cliff every ride?

under load, total pack voltage is all i need to know. if a cell fails, there will be a sudden 2-3 v drop. how can anyone miss that? even a 1 v unusual drop is hard to ignore.

Hi DM, I am neither young nor pushing my pack to far! I just wanted some way to see what the cell balance was like towards the bottom of the charge purely as a way of monitoring the pack over the long term, a way to see if any cell is ageing before another. Even if I balanced charged every cycle it would be nice to see how the cell balance was before charging. So it would probably be better on the charger.
I could probably still read it at arms length without my readers though!!

Sacko, your probably right, that may have been what I had seen, is it available separately, will it do what I need?

So any more ideas on how to do this, or is 4x some 6 or 8s displays the way I will have to go?

Matt Gruber said:

under load, total pack voltage is all i need to know. if a cell fails, there will be a sudden 2-3 v drop. how can anyone miss that? even a 1 v unusual drop is hard to ignore.

Click to expand...

Matt, I like to see the numbers to see how the charge is progressing and also to see how well the cells remain in balance at the bottom of the charge when it goes back on the charger, it can give an early indication of a weak cell which could ultimately prevent further damage to the other cells in each 4p string. On the bike I just rely on the CA for lvc which is set quite high for additional safety and some extra limp back power.

Like dogman, I carry a single Cellog 8M to plug in and test if something suspicious shows up.

That said, if you want cell-level protection under load, you might use the Cellogs and couple them up to your CA to roll off the power on an alarm - then you really don't need an extra display on the bars and can just package the Cellogs away in your pack. The 8S logging variety should do if you want to look at the under-load situation after the ride is over. Cellogs are pretty cool, but it seems there are just enough required power, isolation, and mounting add-ons to make it kind of annoying to use them for built-in cell monitoring...

I could design a board that will bluetooth the data to an Android device, going to require alot of wires though to send every single cell voltage to the board. (One wire/cell). Once that is done, you will need to come up with a waterproof enclosure for it. If you want it to work like that, I can make a start, else I will build it at a later date for my own bike

Sounds like an excellent idea.

If you need a hand, let me know.

I will design it for 37 cell lipo. If you think you need more cells, you can parallel the balance plugs if you have a paralleled pack (if it is safe to do so with your ebike's wiring, if you do it wrong, magic smoke will be released!). I only run 24 cell, but there are some nutcase's on here

Ah, I do need help.

Say for a 4 cell, on the balance plug you measure pins 1-2 for cell 1, pins 2-3 for cell 2, pins 3-4 for cell 3 and so on. So that's quite a few separate ground points I need to deal with, If I use a Arduino Mega as the brain for this thing, that will only have one common ground point instead of 4.

One solution people use is to use voltage dividers. but unless I want to spend all week soldering 74 resistors on my 37 cell monitor, that is not an option!
(And they would probably be tricky to solder surface mount ones due to the space they would take up!)

A LiPo cell is between 3.5 and 4.2 volts, and that is well within the range of what a Analog to Digital Converter chip will accept, without any resistors (They take 0 to 5 volts).

If anyone has a solution to this problem, a wiring diagram would be helpful if its hard to explain

I am sorry about that moody post.

I have always favored KISS in all things. Since I'm stupid, keep it simple.

In practice, a cellog in my pocket is all I need, AND, not having the plugs inaccessible. I can check a cell any time when stopped, pretty quick and easy.

Invariably, I find even a well sorted pack has a cell that is found to be low capacity. Once I know which one, I only need to check that pack out on the road. If it's at 3.65v resting, I know its a matter of blocks left at full speed. At that point, if needing the last drop, I'll put a lv alarm on it to wring it dry as I can without going below 3v.

Since I remove the battery from the bike to charge and store nearly every cycle, I have no problems running the cellog through the entire pack at the kitchen table in comfort. I don't need it part of the bike to scrutinize my pack at end of charge, and detect any cell that has lost capacity in the last two weeks or so. In that two weeks, I will not have done any discharges deep enough for a newly gone bad cell to matter.

Nothing wrong with a nice big font display of all your cells voltages. I would love one if it was as easy as sending HK 15 bucks. I'd love a cellog with a display big enough to just have two of them on the bars.

I was just curious why you felt the need for it. I can see how nice it would be to have it on a cross country tour that did lots of 100% discharges for example.

No worries DM, many thanks for yours and everyone elses replies, another perspective always help you see a bigger picture

Yeah, it's not a mega high priority thing to work on. I am probably going to go with the 70 odd SMD resistor design if I do put it into production since they cost next to nothing I plan on some long distance touring myself, plus I am just a data junkie. I love seeing what is all happening in the inner workings of my ebike.

I did a rough draft in my PCB design software and it looks great, my EBIke will be packed with custom PCB's when its done anyway, so its not a big deal for me.

Being a keen programmer and someone with an interest in Electronics, I wasn't happy about being locked into the CA's closed source firmware (and it's price was a bit higher than I was happy with!).
So I have designed my own and I will release it soon to everyone else after some testing

How's this project going??