Heltec 5A Balancer - remote trigger?

[On_The_Road]

I wanted to trigger my balancers to work via a programable relay on my Victron battery monitor.
I know if you desolder the "Run" bridge on the Heltec you can put a switch there. It seem like the relay of the BMV can supply a NO or NC signal which is 12V. Will that work with the Heltec? Would I have to use the 12V signal from the battery monitor to trigger another relay?


My plan was to have the balancers come on when the battery exceeds 13.5 and turn off at 13.4.

 

[MisterSandals]

Why not put a relay on pin/wire #1 of the balance wire?

 

[On_The_Road]

Why not put a relay on pin/wire #1 of the balance wire?

Ah, Interesting - that is a good idea. Would that extra resistance be an issue for accurate voltage readings for the balancer?

 

[MisterSandals]

Ah, Interesting - that is a good idea. Would that extra resistance be an issue for accurate voltage readings for the balancer?

I don't think so. It would be for the negative only with all the other positive wires being unchanged.

You could always test the voltage thru the relay to see if it is different than without or directly from the battery.

 

[On_The_Road]

One person on a forum reported using the run disconnect feature resulted in a slight discharge current on the balancer.

Breaking the ground connection as you suggested would absolutely deactivate the balancer.

 

[Dynoman]

I wanted to trigger my balancers to work via a programable relay on my Victron battery monitor.
I know if you desolder the "Run" bridge on the Heltec you can put a switch there. It seem like the relay of the BMV can supply a NO or NC signal which is 12V. Will that work with the Heltec? Would I have to use the 12V signal from the battery monitor to trigger another relay?


My plan was to have the balancers come on when the battery exceeds 13.5 and turn off at 13.4.

As you say de-solder the Run bridge and wire a switch to turn on and off the Heltec 5A active balancer.

I use the Victron BMV 712 shunt monitor. The Victron BMV 712 has a dry contact relay (switch) output on the meter display portion and I wired (soldered) it to both sides of the Run pads to switch on/off the Heltec 5A. The BMV 712 is programmed to turn on the Heltec 5A at 27.4 volts and off at 27.2 volts (24 volt system). A 5 minute relay off delay is also programed so not to switch on and off quickly during cloudy days when the battery is in the programed voltage range.

This works well. Before setting up the Heltec 5A to switch at these voltage levels the BMS would cut out on high voltage disconnect at 3.65 volts during battery charge from the SCC in absorb mode at 28.2 volts. Now the batteries are able to be charged to around 28.2 to 28.3 volts for around 20 minutes during absorb and all cells stay less than 3.55 volts before the SCC switches to float mode of approximately 27.4 volts.

 

[MisterSandals]

The Victron BMV 712 has a dry contact relay (switch) output on the meter portion and I wired (soldered) it to both sides of the Run pads to switch on/off the Heltec 5A.

I would love to see a pic of this!

 

[time2roll]

I would connect as described and see how it goes. Worst case need to rewire something.

But honestly once cells are below 3.4 the delta should be low enough that balancing stops. And if by chance the cell delta is large in mid range the battery probably needs to continue balancing.

 

[On_The_Road]

I would connect as described and see how it goes. Worst case need to rewire something.

But honestly once cells are below 3.4 the delta should be low enough that balancing stops. And if by chance the cell delta is large in mid range the battery probably needs to continue balancing.

Ah, interesting - the low Delta acts a shut off - hadn't thought of that.

 

[On_The_Road]

As you say de-solder the Run bridge and wire a switch to turn on and off the Heltec 5A active balancer.

I use the Victron BMV 712 shunt monitor. The Victron BMV 712 has a dry contact relay (switch) output on the meter display portion and I wired (soldered) it to both sides of the Run pads to switch on/off the Heltec 5A. The BMV 712 is programmed to turn on the Heltec 5A at 27.4 volts and off at 27.2 volts (24 volt system). A 5 minute relay off delay is also programed so not to switch on and off quickly during cloudy days when the battery is in the programed voltage range.

This works well. Before setting up the Heltec 5A to switch at these voltage levels the BMS would cut out on high voltage disconnect at 3.65 volts during battery charge from the SCC in absorb mode at 28.2 volts. Now the batteries are able to be charged to around 28.2 to 28.3 volts for around 20 minutes during absorb and all cells stay less than 3.55 volts before the SCC switches to float mode of approximately 27.4 volts.

Thank you for your post....trying to picture what you did...

The BMV head has the NO, NC, and COM ports. Which one did you use? Just one?

I am glad the Heltec helped you out. Good idea on the 5 minute delay. I have a Cerbo also but the relay programing isn't as straight forward as the BMV.

 

[Dynoman]

Thank you for your post....trying to picture what you did...

The BMV head has the NO, NC, and COM ports. Which one did you use? Just one?

I am glad the Heltec helped you out. Good idea on the 5 minute delay. I have a Cerbo also but the relay programing isn't as straight forward as the BMV.

On_TheRoad
@MisterSandals

I have attached a few pages from Manuals and a picture of the Victron app settings for the relay. If I remember right the Heltec 5A is wired to the NO & Com of the Victron BMV-712 display head.

I can tell you that I tried to just wire the Heltec 5A to be on all the time (default out of the package) without any control, but I found that the Heltec 5A would balance the cells mid-charge and when the cells went to absorb voltage of 28.2 for the battery it would trigger a high voltage disconnect at 3.65 volts on some cells because they were to far out of balance for the Heltec 5A to correct.

With the control of Heltec 5A at 27.4 volts on and 27.2 volts off and a absorb voltage around 28.2 volts for 20 minutes and float around 27.4 volts thereafter until lack of sun (24 volt system) there has never been a high voltage BMS disconnect.

Notice that the float voltage 27.4 is above the voltage the Heltec 5A turn off. So the Heltec 5A is balancing the entire time the SCC is in float mode.

My cells are not grade A and during mid charge some times I see 30 to 40 mv differential between the cells so the cells get balanced at mid charge. For some reason this imbalance is greatest around 60% charge and most other times it is 10 mv or less.

Hope this helps...

 

[curiouscarbon]

Why not put a relay on pin/wire #1 of the balance wire?

interesting, have not encountered this solution being documented.

direct connect to battery with relay on Run pins could still slowly drain the pack after Low Voltage Disconnect.

i have a few 4S capacitive heltek active balancers and might try this out.

my concern is that switching the lowest voltage potential pin might result in undefined behavior of the balancer. have you heard of any issues with switching Pin 1 instead of Run?

thanks again for mentioning!

 

[Alkaline]

I've been running the 8s balancer on 3 of my battery packs connected for over 18 months, works fine and cells stay in balance, I have not seen it unbalance the cells, just charge them up once a month and bring them all up to about 3.5V and its good to go.

 

[MisterSandals]

With the control of Heltec 5A at 27.4 volts on and 27.2 volts off and a absorb voltage around 28.2 volts for 20 minutes and float around 27.4 volts thereafter until lack of sun (24 volt system) there has never been a high voltage BMS disconnect.

Our charging philosophies are significantly different. I only charge my cells to 99% (3.45Vpc) and never had any issues with my Heltec. I noticed the LEDs were lit up a couple times when i first installed it but its run on its own without any issues.
Similarly when I float, which is just below where the cells settle after my full charge (settle to 3.35Vpc), i float below that to prevent micro-cycling (3.32Vpc).
I can live without the last 1% of charge and hope my cells live longer because of it. I certainly have removed all the high voltage disconnect issues that are more prevalent when charging to the theoretical limits of LiFePO4 cells.

 

[MisterSandals]

interesting, have not encountered this solution being documented.

I just thought of it when reading the OP in this thread. I've connected quite a few balance wires and have learned from my mistakes!

my concern is that switching the lowest voltage potential pin might result in undefined behavior of the balancer.

I would not describe pin 1 as lowest voltage potential pin. Pin 1 is the negative pin.
Pin 2 is cell 1 positive,
pin 3 is cell 2 positive,
...

Opening the single negative wire seems easiest way to cut off power.

 

[curiouscarbon]

thank you!

 

[Dynoman]

Our charging philosophies are significantly different. I only charge my cells to 99% (3.45Vpc) and never had any issues with my Heltec. I noticed the LEDs were lit up a couple times when i first installed it but its run on its own without any issues.
Similarly when I float, which is just below where the cells settle after my full charge (settle to 3.35Vpc), i float below that to prevent micro-cycling (3.32Vpc).
I can live without the last 1% of charge and hope my cells live longer because of it. I certainly have removed all the high voltage disconnect issues that are more prevalent when charging to the theoretical limits of LiFePO4 cells.

Yes, our charging approach is different and I also don't have any high voltage disconnects since the system is setup as described. The load on my solar system is such that an absorb of the SCC may not happen for weeks to months depending on cloudy vs sunny days. When an absorb cycle does happen the cells are very well balanced. I notice that the more the cells are balanced in the upper knee the cells seem to track better as time goes on and the battery banks do as well. It is my understanding that non grade A cells benefit from being balanced in the upper knee now and then. At least mine do... I do agree that the float voltage of 3.4 to 3.425 volts is on the higher side, but from what I understand is acceptable and it stays there usually for only a few hours. According to the Victron BMV-712 the current is 0 in float after a 1/2 hour or so with some + and some - depending on the loads.

Your way works for you and my way works for me. It's all good. To each his own.

As far as the LEDs being lit up it is my understanding they should always be turned on unless the Heltec 5A is turned off. For example the Heltec LEDs turn on at 27.4 volts and off at 27.2 volts on my system.

 

[On_The_Road]

I understand it now

I was under the impression the relay sent a 12V signal. But it's essentially allowing continuity between it's common and the nc or no. And if you want to use it to signal 12V you would pass 12V through it but not more than 1 amp.

Although, I am measuring 0.9 ohms. It's probably 10 feet of wiring to the BMV head.

Is that too much resistance to introduce into the balancer's ground?

 

[Dynoman]

Yes, it is just a continuity switch.

I have at least 10 to 12 feet of 22 gauge solid wire in use between the Victron BMV-712 head and the de-soldered run pads on the Heltec 5A and all works good. I also have a parallel connection to control two Heltec 5A balancers. I don't know if it is really a ground on the balancer. The wire is just completing the path that the 2 solder pads made with solder in-between them.

Your wire should be good. I do remember that it was a bit of a trick to get the wires inserted into the Victron BMV-712 meter display head. I don't remember the trick, but I found it on Victron's web site. Maybe you wont have any problems. I do remember the solid wire made it easier to insert into the BMV-712 connections and also to solder onto the tiny solder pads of the Heltec 5A.

I did look later last night and I am using the com and NO connections on the back of the Victron BMV-712 meter display head.

Edit: Found the article about inserting wires into the BMV-712 display head. 22 gauge solid wire works good.

How to physically connect wires to BMV-712 configurable relay NO and COM points on back of device
I tried inserting the wire from an unfolded paper clip and the mechanism inside the connector held the paper clip wire. I then pressed on the orange tab and it released the friction and I could remove the paper clip. Originally, I was using a wire that would fit the hole in the connector but was a little too large for the mechanism to hold the wire.

 

[On_The_Road]

So not sure breaking the ground will kill it.

Balancer unplugged and no ground. Plug in balancer. No yellow light. Attach ground. Yellow led lights up.

Remove ground - yellow led stays illuminated.

I wouldn't have expected that.