the easy way to keep your cells balanced is...active balancing

[Daddy Tanuki]

well to get this thread back on track, I ordered and received two of the heltec 15-17 active balancers (capacitor types), and started making a wiring loom for them that will allow me to place the unit away form the battery a reasonable distance.

my battery pack is about 2' x 3.5' (approximately) and the short leads i soldered onto my BMS are already pissing me off. that and the short main cables on the bms.... but I digress.

Everything I have read on the heltecs says that once you hook them up, you cannot unhook them without frying them... why is this? and which harness should i plug in first? The ones I ordered have two plugs. one has B- and B+ 1-8 and the other plug has B+9-17. I quizzed the helltec support site about what to do with the extra lead (B+17) my pack is 2p16s and they said just do not hook it up???? WTF? (honestly their website is worthless but if the unit works....)

I saw other makers of active balancing units where you had to hook up the extras in a particular fashion to keep from blowing the units... so OK... why not the same for this? different architecture?? and why can I not unhook it after hooking it up? (without damage.)

If i were to try to unhook it after words.. which lead should I pull first? I was thinking just cut the negative line as after you take it out the rest of the board would not have a ground so it should not be able to fry anything without a complete circuit. (now you chuckle heads can make fun of my lack of knowledge.)

My 2p16s pack had while undergoing charge with no draw, a maximum divergence of 0.105 volts and that disappeared within 5 minutes of putting a load on the pack. (the bms went into protect and stopped charging. in actuality after watching an almost full charge cycle with it appears I have a runner number 4/5 and a slower to charge cells 11/12 and thats where the real issue was. 4/5 ramped up to 3.51 while 11/12 was at 3.405 and that tripped the alarm for the cell differential? (sorry some of these terms are new to me). BMS was set to max of 3.65 per cell, 58.4 for the pack, with a differential of .100 volts for alarm.

my settings are 54.4 max charge from the SC. I also found out it was drifting higher actually up to 55.36 which I double checked against the BMS and my multimeter, and reset the SC to accommodate the difference between what I was requesting and what I was getting.

as quickly as the cells leveled out with a draw on them i would almost bet that there would not have been any real difference if I had been running the inverter on them to start with. It only appears at the high end while charging (to date).

Currently with two days of overcast skies and running the A/C the entire first 12 hours to dry the cabin out I am at 49% and the high and low voltage difference is only 0.004 volts difference between highest cell and lowest, so I don't think I really need this per se, but I want to see if I can fill the battery a little fuller prior to the BMS shutting down the ports. I am trying to stay in the range of 3.0 and 3.4 volts to avoid the knee's of the curve but I do want to exploit the range as best I can. if I can get in another kilowatt of storage with one of these balancers I am willing to spend the money...hell i already did. and if these batteries pan out then I will probably order another 32 of them and double my capacity. I have the panels for it so why not?

 

[roadrunner]

i got nothing out ofg 4 pages except we now need 2 bms to do the work of one, i thought 1 bms should do everything, if it is a bms, how come the one op posted doesnt balance cells, or do they all work this way

 

[Diysolar123]

well to get this thread back on track, I ordered and received two of the heltec 15-17 active balancers (capacitor types), and started making a wiring loom for them that will allow me to place the unit away form the battery a reasonable distance.

my battery pack is about 2' x 3.5' (approximately) and the short leads i soldered onto my BMS are already pissing me off. that and the short main cables on the bms.... but I digress.

Everything I have read on the heltecs says that once you hook them up, you cannot unhook them without frying them... why is this? and which harness should i plug in first? The ones I ordered have two plugs. one has B- and B+ 1-8 and the other plug has B+9-17. I quizzed the helltec support site about what to do with the extra lead (B+17) my pack is 2p16s and they said just do not hook it up???? WTF? (honestly their website is worthless but if the unit works....)

I plug and unplug mine without a care in the world...no damage at all, and they are just the cheap $30-$40 ones.

for my BMS cables I always make them as a "Y" cable so the BMS always stays attached and I can swap in a balancer or a isdt batgo to look at things directly (the isdt units have a secret calibration menu so you can really adjust them to match your best multimeter) . My cells always sit within a few mv's of each other at 3.400v.

 

[roadrunner]

I plug and unplug mine without a care in the world...no damage at all, and they are just the cheap $30-$40 ones.

for my BMS cables I always make them as a "Y" cable so the BMS always stays attached and I can swap in a balancer or a isdt batgo to look at things directly (the isdt units have a secret calibration menu so you can really adjust them to match your best multimeter) . My cells always sit within a few mv's of each other at 3.400v.

so are you using 2 x bms

 

[Daddy Tanuki]

so are you using 2 x bms

actually yes and no. one is a BMS that offers very limited balancing capabilities. the other technically is not a BMS as it does not do anything except to balance. but it has the capabilities to balance out rather large discrepancies... these are not the fualt of the BMS, but the fact that even though every seller claims tht the batteries are grade A and matched.... at the price points we are buying these cells they are not grade A and Matched... at least not fully matched. I would guess they are grade A- and only loosely sorted but not fully matched. as a result with the size of these cells you need a ability to move more energy than what the actual BMS can move if you want to get as much out of the cells as possible.

I honestly do not needs this, but its cheap under 50 bucks and its a learning experience...+ my batteries cost me around 5K USD with shipping.... whats 50 bucks to add a second layer of protection to the pack? penny wise and pound foolish is a term that comes to mind.

in the end, this is just a lark. I could pay about 10K initially and get put back on the grid... what my down the road costs would be as more folks leave the area are not something I can guestimate with the service provider in my area.

 

[Sanwizard]

Anyone have experience with the HelTec SmartBMS? BMS with built-in active balancing and supports CANbus/RS485 communication. Seems like it would be good. I'm thinking of cancelling my order for Overkill 48V BMS and get these instead.

The website is hilariously terrible. But if the product is good and price is reasonable, who cares?

13-24S Smart BMS with 0.6A 1A 2A Active balancer

[vc_row][vc_column][/vc_column][/vc_row]

heltec-bms.com

Category: SMART BMS SKU: 1026
Tags: 13-24S 200A Bluetooth Smart BMS with Active balance
Li-ion Lipo Lifepo4 LTO Smart BMS Lifepo4/LTO/Li-ion/Lipo
Support CAN / RS485 interface (optional) BMS


Edit: Oops I should have searched first. There's a dedicated thread for these:
https://diysolarforum.com/threads/heltec-jk-200a-smart-bms-with-2a-active-balance.17831/unread

They work great, but for large cells, use the 2amp balance version. My system stays around .008mv deviation most of the time.
The packaging changed a bit from last year. Old on left, new on right.

 

[kaspre]

They work great, but for large cells, use the 2amp balance version. My system stays around .008mv deviation most of the time.
The packaging changed a bit from last year. Old on left, new on right.

Thanks, I just received my order a couple days ago. Same comical misspelling of "Balance" and documentation is weak, but otherwise the build quality seems solid. I need to get some cables and accessories this week, but hopefully will get my batteries assembled and ready for some testing soon.

 

[kaspre]

They work great, but for large cells, use the 2amp balance version. My system stays around .008mv deviation most of the time.
The packaging changed a bit from last year. Old on left, new on right.

Did you keep the cell monitoring cables the same length for each cell, or trim them to length from BMS?

I was planning to trim mine to length from BMS, so that the nearest cell would have a shorter cable and the farthest cell would have a longer cable. That would keep my wiring loom nice and neat. But then I was reading the Victron wiring guide about how cable length impacts voltage drop & current delivery, and now I'm thinking maybe I should keep all leads the same length, and just try to coil any excess out of the way.

Or perhaps it wouldn't make any difference on these short wire lengths? Maximum difference is about 24 inches. I'm trying not to overthink every little detail, but I don't want to miss anything important either. If the BMS is relying on these readings then I suppose I should ensure they are as accurate as possible, and so now I'm leaning toward keeping 28" wires for even the shortest, 4" runs.

 

[Horsefly]

Did you keep the cell monitoring cables the same length for each cell, or trim them to length from BMS?

I was planning to trim mine to length from BMS, so that the nearest cell would have a shorter cable and the farthest cell would have a longer cable. That would keep my wiring loom nice and neat. But then I was reading the Victron wiring guide about how cable length impacts voltage drop & current delivery, and now I'm thinking maybe I should keep all leads the same length, and just try to coil any excess out of the way.

Or perhaps it wouldn't make any difference on these short wire lengths? Maximum difference is about 24 inches. I'm trying not to overthink every little detail, but I don't want to miss anything important either. If the BMS is relying on these readings then I suppose I should ensure they are as accurate as possible, and so now I'm leaning toward keeping 28" wires for even the shortest, 4" runs.

The resistance of say AWG 24 stranded wire is about 26 ohms per thousand feet. So the resistance difference between a 28" run and a 4" run (2 ft) is 2 x 26/1000 = 0.052 ohms. If you have 2A running through that wire, the voltage drop difference is 2 x 0.052 = ~0.1V. That's enough to make a difference if you are trying to keep your cells balanced to within something like 0.005V. So yeah, it's good to keep the balance leads close to the same length.

Note that this only matters if you have an active balancer (or a BMS with active balancing). On the more run-of-the-mill BMS the passive balancing is small enough in current that the voltage drop is pretty insignificant.

 

[Sanwizard]

The resistance of say AWG 24 stranded wire is about 26 ohms per thousand feet. So the resistance difference between a 28" run and a 4" run (2 ft) is 2 x 26/1000 = 0.052 ohms. If you have 2A running through that wire, the voltage drop difference is 2 x 0.052 = ~0.1V. That's enough to make a difference if you are trying to keep your cells balanced to within something like 0.005V. So yeah, it's good to keep the balance leads close to the same length.

Note that this only matters if you have an active balancer (or a BMS with active balancing). On the more run-of-the-mill BMS the passive balancing is small enough in current that the voltage drop is pretty insignificant.

Agree. All my balance cables are the same length. The connection is just as important. A just bought some silver paste to improve the connection to lower the wire ohms on the BMS.

 

[Steve_S]

Lesson Learned DEPT:
I have Active Balancing on ALL of my packs and future packs will also, now a default add, regardless of Matched & Batched or Bulk Commodity cells. DO keep the wire lengths identical, or you WILL be chasing Gremlins... Never offer Gremlin's a Foothold or they will make life "interesting" and generally in an unpleasant manner.

 

[sethyferg]

I run 24V, all of my battery packs have a QNBBM-8S Active Balancer on them and they work quite well to keep everything nicely balanced.
Passive Balancing is essentially useless on large capacity LFP as it only burns off hi voltage cells at low power by dissipation. There have been some recent imrovement's on Active Balancers by Known Good vendors like Heltec & QNBBM (deligreen :-( ).

A NOTE: Be certain that the Active Balancer you select has enough capacity to handle the Size of your cells ! As Active Balancers transfer power between cells, the larger capacity cell balancing has to work more.

I have done extensive cycle tests & thrash testing of my packs with the QNBBMs and they take it all quite well. Thrash Tests included full C-Rate charge & discharge runs as well as other stress tests.

Charge Setting Note: (I use a Midnite Solar Classic SCC)
Absorb: 28.2 for 15 minutes
Equalize: OFF
Float 27.9V
MIn Volts: 22.0 Max Volts: 28.7
Rebulk Voltage: 27.7
End Amps: 14A
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

* Active Balancing + Float:
I've found that once the battery packs are "full" and in float mode, they barely take any input but as the Active balancers are working and levelling, the float allows for everything to fully top off evenly, all cells within all packs are between 6-10mv once float has been running for an hour. This is what I have observed with my packs.

Hope it helps, Good Luck

Hello! May I please ask which size of active Heltec balancer I would need for a 4S 420ah LiFePO4 battery pack? Thanks so much for your help : )

 

[Steve_S]

Hello! May I please ask which size of active Heltec balancer I would need for a 4S 420ah LiFePO4 battery pack? Thanks so much for your help : )

5A Active Balancer can handle up to 300AH Cells
This is the simpler 3s/4s Active Capacitance Model.

This product is no longer available.

This product is no longer available.

cncdheltec.en.alibaba.com

 

[Baserati]

I use a Heltec Capacitor Active Balancer from amazon or aliexpress. Be careful when you use a capacitor active balancer , make sure you pre-charge the capacitors before you hook it up to your battery, I use a resistor on the negative lead to pre-charge the capacitors before I connect up the negative lead to the battery. With my first balancer I forgot to do that and I burned up one of the capacitor.

Can you share details of how you pre-charge the capacitors. Did you use a power supply and what value resistor? How did you set up the wiring?.

 

[Sanwizard]

Can you share details of how you pre-charge the capacitors. Did you use a power supply and what value resistor? How did you set up the wiring?.

Please search for the precharge video by Will. Fairly self explainitory

 

[Baserati]

Please search for the precharge video by Will. Fairly self explainitory

Could not find it

 

[Horsefly]

I use a Heltec Capacitor Active Balancer from amazon or aliexpress. Be careful when you use a capacitor active balancer , make sure you pre-charge the capacitors before you hook it up to your battery, I use a resistor on the negative lead to pre-charge the capacitors before I connect up the negative lead to the battery. With my first balancer I forgot to do that and I burned up one of the capacitor.

I'm not sure this makes any sense. The original pre-charge idea (which I think has some merit) was based on the really huge capacitors on the front end of larger inverters. It kinda got a life of its own, but I guess it is OK. To extend this to the active balancer - which has really small capacitors - seems kinda crazy.

For the record, I've dry connected my capacitor-based Heltec active balancer several times. Although I've noticed a small spark, I've never seen anything requiring a pre-charge.

Don't make this harder than it is. KISS - Keep It Simple, Stupid.

 

[Sanwizard]

Could not find it

 

[Baserati]

Ok so this is what I am thinking of doing 16S pack

Connect all positive leads of active balancer to each cell (Sam as BMS)
Connect negative lead of cell to resistor I have a 6.8 ohm at hand. Is that too low
Connect negative lead to battery

Let me know if this sounds right

 

[chrisski]

Ok so this is what I am thinking of doing 16S pack

Connect all positive leads of active balancer to each cell (Sam as BMS)
Connect negative lead of cell to resistor I have a 6.8 ohm at hand. Is that too low
Connect negative lead to battery

Let me know if this sounds right

I would just recommend getting an oversized resistor, like Will has in his video that you can use at some later date for a large inverter. I am looking at a 25 watt 30 ohm resistor to hook up a 3000 watt inverter. That would be the resistor I use for anything under 3000 watts I'm afraid of creating a spark for. 5 Amps is next to nothing for that Heltec Active Balancer.

Kind of a harmless thing though.

We had a capacitor at work for a piece of test equipment. Was about the size of a tall boy, 24 oz beer can, at least that's how I remember it from 30 years ago. When we worked on that, we'd always be told not to short the leads or it could kill you. Don't know if its true or not. I would not use a resistor and my bare hands for that. The Heltec capacitors I would not fear for my life with those capacitors. For the video Will showed with that huge inverter, I would not short a resistor like that without seeing someone else do it. After I know its safe, I'll try it. I've never been much of a blazing new trails kind of person, especially when money or my life would be on the line. Never the first to jump off a bridge.