Heltec BMS' (up to 350A) with Active Balancing & Independent Active Balancers

[fafrd]

I would be very disappointed if these Heltic BMSs with active balance couldn't handle 80A discharge.
I know Heltec had a bunch of really cheap non smart BMSs on their website. I don't know which one you have.
Chargery seems to be good for high amps but I hear plenty of complaining about them too.

To be fair, the BMS handled 80A no problem for 1 hour continuous, but I need a BMS that can handle 80A indefinitely (at least 20 hours straight).

Also, it appears that particular unit may have had a manufacturing defect (P- bus bar only soldered at very ends, largely unsoldered to landing pad on board.

I had the best of their non-smart 8S BMSes (300A discharge 100A charge).

What I am attempting to clarify with their engineers is what current limit can be accommodated under continuous discharge relying on passive-cooling only at 25C ambient.

Whether they tell me that particular BMS was defective or not, if the answer comes back that better cooling is needed to discharge 80A continuous, I’ll probably switch to a separate-switch BMS like the Daly.

For sure, a smart BMS like the model you have should give you plenty of warning that it is overheating before any damage is done.

But the thing I learned that you may want to consider is that it is worth stress-testing your BMS before you get everything installed.

So if iou think your BMS should handle 80A continuous I’m whatever highest temps you expect it to operate in, I’d highly suggest you stress test it at that level first...

I’d be interested in any complaints you can share regarding Chargery...

 

[Gazoo]

Overkill claims his BMS's can handle their current ratings continuously His warranty can't be beat. If there is smoke he will replace it or refund. If interested PM him to confirm, but that's what he told me. The passive balancing is pretty much worthless with these large cells. I don't see this as being an issue since most of us use our cells within the knees. And if drifting between the knees starts to look unhealthy, one can always add active balancers later on.

I have also noticed Chargery complaints. If you want to know more search the forum.

 

[fafrd]

Overkill claims his BMS's can handle their current ratings continuously His warranty can't be beat. If there is smoke he will replace it or refund. If interested PM him to confirm, but that's what he told me. The passive balancing is pretty much worthless with these large cells. I don't see this as being an issue since most of us use our cells within the knees. And if drifting between the knees starts to look unhealthy, one can always add active balancers later on.

I have also noticed Chargery complaints. If you want to know more search the forum.

So far, Heltec seems to be honoring their warranty, so warranty alone is not a reason for me to go one way or the other.

Avoiding a failure once operational is my highest priority.

So I want to understand what these all-in-one BMSes can handle as far as truly continuous operation at some % of rating achieving at least 100A with ambient cooling only at 25C.

If Heltec and/or Overkill have run those tests. I can be convinced to stick with an all-in-one.

If they say there is some limit on continuous hours of use without adding better cooling such as a fan, I’ll consider it but at that point, a seoerate switch with it’s own temperature monitoring and active cooling sure starts sounding more appealing...

I’ll read up on Chargery before jumping ship and I’ll also start thinking about how an all-in-one can be used to control an external switch rather than battery ground...

 

[Bob B]

Just to note .... any post about the Chargery BMS that are more than a couple of months old are mostly irrelevant since they have made significant improvements via firmware updates.

 

[ArthurEld]

I point a pedestal fan at my stuff any time I am concerned about heat.
It is a cheap way to keep fresh cool air circulating

 

[Gazoo]

Just to note .... any post about the Chargery BMS that are more than a couple of months old are mostly irrelevant since they have made significant improvements via firmware updates.

Has support improved.... Sorry, couldn't resist. Besides from what I recall most of the issues were centered around the 16T version.

 

[Bob B]

Has support improved.... Sorry, couldn't resist. Besides from what I recall most of the issues were centered around the 16T version.

Jason has been responding to people reporting problems on this forum .... I have had good luck emailing Jason directly .... Several changes have been made to the product based on suggestions from the forum .... some within a few days. Time will tell what the new active balance product looks like, but from what I understand it should be released some time in February.
Any complaint I had about my BMS8T has been resolved.
I would like to see a wireless communications option, but no idea if that is in the works or not.

 

[ArthurEld]

Not reporting accurate information was one complaint I heard often about Chargery.
The separate contactors or relays aren't popular for everybody either.
But Chargery is probably the most popular BMS for people using high amps.

 

[Bob B]

Not reporting accurate information was one complaint I heard often about Chargery.
The separate contactors or relays aren't popular for everybody either.
But Chargery is probably the most popular BMS for people using high amps.

Could you post a reference to that .... I'm not remembering such complaints.
I'm using my Chargery to switch devices via remote control rather than interrupt the battery current. I never did like the idea of a high power relay which used a lot of coil current ... or disconnect the battery from charge controllers or inverters.

@Steve_S has implemented the DCC controllers and pushed them pretty hard and they seem to work very well for him. Steve has several packs in his configuration, so it is pretty hard to get around switching the battery current.

 

[ArthurEld]

Could you post a reference to that .... I'm not remembering such complaints.

Here's two but there are more

Checking Chargery voltage measurements

This is a heads up for Chargery as they are redesigning their BMS. Chargery has a red ribbon cable which attaches to each of the cells to measure cell voltage. There's a problem with this mechanism as power is drawn from the ground voltage sense cable and the last sense cable connection...

diysolarforum.com

Chargery: AH measurements

I've been working on a DIY Coulomb counter. https://diysolarforum.com/threads/coulomb-counter-for-diy-bms.11610/ I've noticed the Chargery SOC and AH counts were way off base. With the Coulomb counter complete, here's a comparison of my counter and Chargery's serial data. The entire test...

diysolarforum.com

 

[Bob B]

Here's two but there are more

Checking Chargery voltage measurements

This is a heads up for Chargery as they are redesigning their BMS. Chargery has a red ribbon cable which attaches to each of the cells to measure cell voltage. There's a problem with this mechanism as power is drawn from the ground voltage sense cable and the last sense cable connection...

diysolarforum.com

Chargery: AH measurements

I've been working on a DIY Coulomb counter. https://diysolarforum.com/threads/coulomb-counter-for-diy-bms.11610/ I've noticed the Chargery SOC and AH counts were way off base. With the Coulomb counter complete, here's a comparison of my counter and Chargery's serial data. The entire test...

diysolarforum.com

The cell voltage measurements and the coulomb / SOC tracking are both resolved in the current update. Chargery is now also selling an external power board to further improve voltage readings by removing the power for the unit from the balance leads. I did the external power by using a Schottky diode .... that solution is in their newest documentation.

These are examples of what I call old news since these issues have been resolved.

 

[Gazoo]

Jason has been responding to people reporting problems on this forum .... I have had good luck emailing Jason directly .... Several changes have been made to the product based on suggestions from the forum .... some within a few days. Time will tell what the new active balance product looks like, but from what I understand it should be released some time in February.
Any complaint I had about my BMS8T has been resolved.
I would like to see a wireless communications option, but no idea if that is in the works or not.

But what happens if one receives a defective unit? I could be wrong but it's my understanding one has to pay for shipping both ways, and the cost is more than that of a new unit. By new unit I mean just the guts, not the meter, relays or anything else.

 

[fafrd]

Not reporting accurate information was one complaint I heard often about Chargery.
The separate contactors or relays aren't popular for everybody either.
But Chargery is probably the most popular BMS for people using high amps.

Didn’t realize that.

What constitutes ‘high amps’?

I’m charging at 45A today but building to charge at 80A or even 100A tomorrow and my discharge will be at at 80A for 5 hours continuous with occasional spikes to as much as 180A during extended power outages.

Would you guess that puts me into the ‘high amps’ club?

 

[GXMnow]

So you measured 1 mOhm @ 29A meaning a voltage drop of 29mV @ 29A and you are projecting that you’d measure an 80mV voltage drop at 80A (but have not confirmed that with measurement), right?

I measured the voltage drop at 20, 35 and 80 amps, in each case it was very close to 1 mOhm or 0.001 ohm . So yes, it was about 80 vm across the BMS leads at 80 amps. And I suspect a fair bit of the resistance is actually the wires. The two #7 awg wires seem a bit light for 200 amps.

 

[ArthurEld]

Didn’t realize that.

What constitutes ‘high amps’?

I’m charging at 45A today but building to charge at 80A or even 100A tomorrow and my discharge will be at at 80A for 5 hours continuous with occasional spikes to as much as 180A during extended power outages.

Would you guess that puts me into the ‘high amps’ club?

I wouldn't put you in the high amps club but you do need a good BMS.
Off grid up north heating in winter uses high amps. A lot of people use high amps for 12V and 24V

 

[fafrd]

I measured the voltage drop at 20, 35 and 80 amps, in each case it was very close to 1 mOhm or 0.001 ohm . So yes, it was about 80 vm across the BMS leads at 80 amps. And I suspect a fair bit of the resistance is actually the wires. The two #7 awg wires seem a bit light for 200 amps.

If you measured 80mV voltage drop through your Heltec BMS discharging 80A, that’s all the confirmation I need that the BMS I received was defective.

Resistance actually the #7 wires I don’t understand - didn’t you measure directly on the P- and B- terminals of the BMS? Is your BMS encased in plastic so you had to resort to measuring at the lugs connecting to the battery - terminal and - cell terminal?

If your #7 wires came preassembled and you can estimate length for me, I can estimate what number of those 80mA you you measured were across both wires...

 

[fafrd]

I wouldn't put you in the high amps club but you do need a good BMS.
Off grid up north heating in winter uses high amps. A lot of people use high amps for 12V and 24V

Yeah, I’m trying to build my system at 24V because I’m dealing with severe shading issues and will get better output from a 1S PV array than a 2S array...

Since the battery is the heart of the entire system, I need to assure it is up and running continuously and a more-than-basic BMS probably makes sense.

Just heard from another Firum member that he saw an 80mV drop at 80A on his Heltec BMS, so the 450mv drop I saw was almost certainly an indication of a defect. And it seems he was measuring at the end of 2 #7 wires which should have contributed about half of the 80mV he measured (assuming there were 2 #7 wires on each of P- and B- and those wires were all about 1 foot long.

As I already may have posted, the P- busbar on the BMS appears to not be soldered to the pad on the main board over most of it’s length.

I have no idea whether a defective solder joint could contribute another ~5 mOhm of resistance, but if so, that could be all it takes for the BMS to be dissipating 36W @ 80A instead of 6.4W or 3.2W...

Using the same 0.5 Ohm P- to B- resistance at 300A of current (the other 9.5 mOhm of resistance being in the #7 wires) would translate to 40W of heat being generated by the BMS running flat-out at 300A. So even though I was only running 80A I was generating as much heat as a non-defective BMS would be generating at max 300A and if these BMSes push the specs as to what they can achieve with passive-cooling only, an hour at 36W could easily be all it takes for one of these basic BMSes to overheat...

 

[ArthurEld]

Heltec would probably rather give you a deal on the smart BMS with active balance instead of giving you your money back.

 

[fafrd]

Heltec would probably rather give you a deal on the smart BMS with active balance instead of giving you your money back.

Yeah, I would not ask for a refund. It’ll either be a straight up replacement Oran upgrade to a smart BMS like yours depending on what they tell me about expected performance.

The maximum charging current on your BMS remains a concern, however. Chargery is far better in that department (full 300A in an out, up to 600A with a bigger switch if you need it)...

Longer-term, I’ll be adding more PV panels, so I’d like y to I be able to safely charge 24V up to 100A...

 

[Bob B]

But what happens if one receives a defective unit? I could be wrong but it's my understanding one has to pay for shipping both ways, and the cost is more than that of a new unit. By new unit I mean just the guts, not the meter, relays or anything else.

I don't know ... I haven't had to return anything to them .... but, isn't that the risk we take when buying any product that ships from China?

The last problem I remember that looked like it may have been a BMS problem .... I'm pretty sure that @Sipma02 said after exchanging emails, Jason had agreed to send him a new BMS.