OpenEnergyMonitor Community


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The wires will be a few inches long at most. The balancers will be mounted to the side of the cells, with a small air gap to allow natural convection to cool the back of the board when the resistors heat up, and prevent that heat from transferring to the cells (although my cells are massive, 180Ah LFP’s)

Thank you Stuart.

I understand that ordering directly from JLCPCB will be cheaper, but one needs to go in the process of ordering at JLCPCB, perhaps need to switch components (different brand resistor, same value) if something is out of stock, and order attiny 841 from different sources.

All that work needs to be compensated + stock and tax things.

You think it’s possible to share the mouse bite on GitHub?
(I did not check if you already did)

For me needing more then 10 additional, it would be a great help.

That is sad.

The PCF8574T is not expensive, but (!)
Buy separate from mouser (expensive but fast) or AliExpress (cheap but take long time) the $2 does not compensate the real costs.

You probably paid with PayPal.
Good reason for full refund and order 5 new boards


S13 is 13 modules.

Solder the Attiny841 is a pain.
If you can get your hands on some solder paste, it is much more easy.
Otherwise I hope you bought a few spare Attiny841…

If you read about 20-30 post back [post no. 2570: DIYBMS v4], Stuart shared a video link on how to do with frying pan if you have no heat gun.

With soldering iron it is difficult.
Really difficult.

Solder paste and hot air works just fine.

[edited to add link - Moderator (RW)]

I managed to use solder paste and flow it with a soldering iron, see my post above for the result. Solder paste was ordered from AliExpress, costs just a few bucks. Use a tiny tiny amount. Working under a magnifier helps as well.

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Sorry to hear about the problems at JLC @UTima

I’ve not had any problems so far, but with the volume of boards they generate I expect they also get a fair share of failures.

Did you not order the board with the resistors populated?

If you need to purchase a single fully populated controller, the OEM shop now sells them - this saves you ordering 5 boards and waiting for shipping from China. []

Just in time, ordered, any recommendations for WeMos D1 mini Pro ?

Its a bit of a wild west on those, if you are lucky Amazon have them, but a lot of people have ended up with clones with incorrect power supply chips (too low current).

Yes it would. Its work in progress. I’m trying to tidy up a few threads now.

I am medium skilled at soldering PTH and this was my first try. Very successful.
0. Use a lot of flux!!!

  1. Just solder some solder on one edge pinpad
    2a. heat it while you push the ic on it with the other hand until its in good position
    2b. heat the diagonal pin and take very little solder to secure the chip
  2. Take some (little amount) solder with your soldering iron and drag it over the pins

Only safe place is direct

I buy a few at a time.

@TrystanLea @glyn.hudson could the shop stock genuine ones?

Interesting the version on the website (v2) now comes with a “Lithium battery interface, 500mA Max charging current”

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Sure, we could stock a few, Just to double-check is this the correct one:

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@stuart is this the right one?

No - thats the 4MB version not the “pro” one.

This one appears to be the official one…

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Hi Keith picked up on you saying you use a flat pack power supply Is this the Eltek flatpack early version.
I use this at the moment and have some infomation
That may help you I adjust it’s voltage to modulate current output by writing to the Controler rs232

Hi @Bill_Burgess, I’m currently using the 2000w Flatpack 2 HE (the black one) and attempting to communicate with it over canbus. By controller I’m guessing that you have the Eltek Smartcontroller?
I’ve been able to charge the packs directly using the flatpack however the default voltage output is measured at 53.8, so when my 14s system approaches 3.8v / pack the charge rate drops away. As a result I’m using 3 cheapo MPPT charge controllers to handle charging and deliver an extra level of protection. Mains to charge controller output efficiency is generally around 90-95% which I’m happy with and the Flatpack is much more efficient than the desktop PC power supply I was using before which was around 70% efficient.

Ultimately I was hoping to charge directly from the Flatpack set at around 57v and limit current via canbus control in real time so that I’m only charging the batteries with surplus solar power. This could be handled by an emontx2 I have close to the battery, or it could be a branch to the day BMS code.

Any advice you have is greatly appreciated though as currently two canbus shields have not worked for either a stock arduino or an emontx2 running at 3.3v.
With the new forum structure I’m thinking we might need to move this conversation across to solar charging too? :grinning:

Hi Keith
Sounds like you have the later units
The ones I use are the 1500w units.
With the Controler . This lets me talk to the Controler via rs232. And adjust things .

I take it that you have only the rectifier modul that you are connecting to . As it sounds like it has defaulted to its stand alone voltage .
I have not tried to talk directly to these units by can bus as yet
I will make some enquires with a few ppl I know to see if I can get any infomation to help.
Yes the later telco type rectifers are a lot more efficacy based now than before

Regards. Bill

Hey fellaz,

About to place an order for 30 main boards and 10 controller boards when it occurred to me that I would have to provide my own low voltage disconnect…

I would prefer to use some mosfets but using a mechanical option isn’t out of the question…

Just curious one everyone’s else solution.

I’m going to be installing the diyBms on my large 7s100p (+/-) battery pack. Ive built my packs in 40cell parallel groups which I will string together in order to get 7s100p.

Is there a simple solution to raise the balancing current one the diybms? Maybe connecting some large power resistors to the diybms board?

Thx guys for your help.


Why do you need 10 controller boards?

You are building 7s40p and then putting 3 strings together to get 7s120p.

A single controller will control up to 4x 16 modules. You will only need 21 modules.

JLCPCB have limits on the quantity of orders at the moment (production issues), although the OEM shop has them in stock at the moment, ready for shipping from the UK so no need to wait for China post!
Link here… []

The controller can drive relays and does have “low cell voltage” and “low pack cut off voltage” rules.