diy solar

diy solar

Heltec balancer

shavermcspud

Solar Enthusiast
Joined
Mar 12, 2020
Messages
567
Hi, thought id try out these active balancers people have been discussing. I have connected up the balance unit to a spare purposely unbalanced 16s 280ah LFP pack and it doesn't appear to be working at all, the run light comes on, on the connectors measure fine with a multi meter but it doesn't balance the pack at all, I have left it on a non used pack at 3.45v per cell with a 70mv difference and its been like for over a week and not changed at all, I can hear the whining noise likes its doing something.
 
Do you have a clamp meter to check it, the most I saw when testing was 1.54 amps.
 
Hi, thought id try out these active balancers people have been discussing. I have connected up the balance unit to a spare purposely unbalanced 16s 280ah LFP pack and it doesn't appear to be working at all, the run light comes on, on the connectors measure fine with a multi meter but it doesn't balance the pack at all, I have left it on a non used pack at 3.45v per cell with a 70mv difference and its been like for over a week and not changed at all, I can hear the whining noise likes its doing something.
First, you should use a multimeter to measure cell voltage using the same instrument. Measure directly on the balancers ‘sense’ leads so you are measuring exactly the voltages it is seeing.

Since individual channels have +/-5mV accuracy, take actual max - min voltage difference and subtract 10mV for worst-case delta.

Balance current is ~100mA per every 10mV of delta, so if your 70mV delta assumption is correct, the minimum balance current should be ~600mA.

If you have run your balancer for ‘a week’ meaning 168 hours straight. 600mA of balance current would translate to 100.8Ah or 36% of battery capacity, so either you have not been operating it for that length of time on a quiescent battery (no charge current being put in or discharge current being taken out), or it is defective.

I only connect my Heltec active balancer after LVD when the (bottom balanced) battery is discharged and it works exactly as expected.

If you are too-balanced, it should only be connected while the battery is being held in float and disconnected as soon as the battery discharges below that level.

Because these Heltec Balancers are operational throughout he full charge curve, it is important to disconnect them before you discharge below float voltage or they will screw up the balance.

I have a cheap voltage monitor with relay controlling the ON contact on mine so that I can control / program the voltage levels where the balancer is ON…
 
I only connect my Heltec active balancer after LVD when the (bottom balanced) battery is discharged and it works exactly as expected.

If you are too-balanced, it should only be connected while the battery is being held in float and disconnected as soon as the battery discharges below that level.

Because these Heltec Balancers are operational throughout he full charge curve, it is important to disconnect them before you discharge below float voltage or they will screw up the balance.

I have a cheap voltage monitor with relay controlling the ON contact on mine so that I can control / program the voltage levels where the balancer is ON…
I have different thoughts on this top vs bottom balance.

If I am in a situation where my battery is bouncing off the top daily, I prefer to have it top balanced. If I get in a situation where the battery will be bouncing off the bottom for a few days or weeks I would prefer to have the battery better balanced at the bottom. Seems like the active balancer would accomplish this automatically. A rare once to the bottom for a few hours would not seem to completely throw off the top balance. In the middle 80% the cell voltage delta should be small enough that there is virtually no activity.
 
I have different thoughts on this top vs bottom balance.

If I am in a situation where my battery is bouncing off the top daily, I prefer to have it top balanced. If I get in a situation where the battery will be bouncing off the bottom for a few days or weeks I would prefer to have the battery better balanced at the bottom. Seems like the active balancer would accomplish this automatically. A rare once to the bottom for a few hours would not seem to completely throw off the top balance. In the middle 80% the cell voltage delta should be small enough that there is virtually no activity.
Totally agree with everything you have stated, but only in the case that the charge & discharge curves of your cells are well-matched throughout the ‘flats’ (meaning maximum voltage mismatch between cells is very small and thus any balance currents over ~85% of the charge or discharge cycle will be inconsequentially small as well).

I wish my cells were well-matched in that way but they are not. I have two cells that hit the little ‘mid-bump’ halfway through the flats much earlier than the others and then slow down allowing the other cells to catch up a few hours / ~15-20% SOC later.

I’ll always have a delta voltage of at least 20mV midway through the flats and can sometimes have even more.

20mV should translate to ~200mA of current which even over 3 hours should translate to no more than 0.6Ah or just over 0.1% of my 560Ah battery, so you have a point that my concern may be misplaced.

But after finally getting my battery perfectly bottom-balanced, I wanted to use the precious few hours I have every night after the battery has been discharged and before solar charging starts the next morning to compensate for any mismatch in self-consumption, rather than also ‘undoing’ whatever ‘false flag’ balance charge was redistributed in the middle of the flats.

This also allows me to monitor the mismatch in self-discharge - if the same cell keeps dropping below the others by LVD and that gap steadily increases over time, I know that cell is starting to get worse and may need to be replaced…

This whole same approach can apply equally-easily to top-balance as I’ve applied it to bottom balance - it just means programming a sense relay to only turn on the Active Balancer once the battery has charged up above the upper charge knee (or at least the Float Voltage).
 
Back
Top