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Why not to use Daly BMS with MPPT controllers

Does this look right? Excuse the amateur drawing skills. Obviously, I would not hook up the PV panel intentionally but in case of an MPP failure, I think this would be the circuit.

NOTE: Edited to remove image with incorrect wiring diagram. See the diagram by @BradCagle in the following comments.
 
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Thank you so much for clarifying @BradCagle . It makes perfect sense. I was thinking the controller needed 12v but of course, it has to have the battery voltage to control it. I sure appreciate the help.
 
I ended up taking @crossy 's proposed solution a bit further. I had some PC boards made to make an easy build of it and added a couple more features.

A miniature SSR can provide control to an active cell balancer at the upper knee of the cell charging graph. ON at (~3.40v/cell) and OFF at (~3.35v/cell).

If the board senses average high voltage (~3.55v/cell) at the main battery +/- terminals, it shuts off the PV panel SSR and at the same time triggers a remote mounted piezo alarm as an alert until average battery voltage drops low (~2.95v/cell).

Provision for up to three PV array SSRs (all three SSRs trigger OFF or ON at the same time).

An off/on switch controls power to the board, which in turn shuts off the PV arrays. The board is protected by a 250mA resettable fuse.

The DC-DC buck converter installed in the pic below has a max 40v input. 60v buck converters are available with the same footprint for higher battery voltages.

The 40A SSR w/heatsink was the most expensive part, $13 at Amazon. All together, a very budget friendly solution. Special thanks to @crossy !!!

Battery HV Protection Board.jpg
 
@Davismltc Nice job, good to see my design in the flesh so to speak. :)

I do like the idea of controlling the active balancer. Ours is operational all the time, I'm not sure if we are actually losing significant amounts of energy via the beast (our cells are "somewhat" worn and mis-matched), plenty of spare ports on the coulomb-counter for some controls.
 
There's an Australian fellow on Youtube, "Offgrid garage", that has newer cells. He found running an active balancer all the time was causing more imbalance, as compared to only running one at the upper knee. I think it could also depend on how low the battery is utilized before recharging, and if it's capacity is being limited by the lowest cell voltage. If the cells aren't matched very well, running a balancer all the time may be beneficial.
 
I don't think a fixed duty cycle will work great, it's not as simple as 50% duty cycle will give you half the voltage. You need to have feedback voltage loop to maintain the correct voltage because the load dictates the voltage

I guess if you know the load very well you can size the inductor/capacitor correctly, and experiment with the duty cycle to get it right. But the buck converter will be tuned only for the given load. Change the load, and if it's too small you might get full input voltage, on the output.
Yea. would need a minimum load. Vicor produces buck converters that are open loop. They are called intermediate buss converters.
 
I forwarded this thread to my friend/supplier who in turned posted it to a local supplier discussion forum. Unfortunately for him, said forum was mostly Daly fanbois (suppliers) and immediately reacted to the title of the video before watching the content.

My friend got kicked out of that discussion forum.
Simply put, the title of the video was insinuating Daly at fault.
Nonetheless, I learned a lot of lessons in this thread.
#1. faults can happen everywhere. be prepared.
#2. dont argue with fanbois. dont buy from fanbois.
 
I forwarded this thread to my friend/supplier who in turned posted it to a local supplier discussion forum. Unfortunately for him, said forum was mostly Daly fanbois (suppliers) and immediately reacted to the title of the video before watching the content.

My friend got kicked out of that discussion forum.
Simply put, the title of the video was insinuating Daly at fault.
Nonetheless, I learned a lot of lessons in this thread.
#1. faults can happen everywhere. be prepared.
#2. dont argue with fanbois. dont buy from fanbois.

Yeah, the title is just wrong as this can happen with just about any MOSFET switched BMS
 
Is this for a 12v, 24v variant?
Mine is a 4s (12v) model: JBD-SP04S020-L4S-120A-B-U (v 1.0)
The owner's manual they sent me says operating voltage is 14.6v max.

I don't know about the 8s (24v) one.
 
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I had a Victron mppt controller fail short on its outputs. ( due to lightening ) It blew the fuse it its circuit to the battery , but the PV voltage did not appear on its output ?

I would have thought a big TVS diode and fast blow fuse would survive for medium size systems , the key is to isolate the SCC until manual tests can be carried out. Of course killing the battery feed to sone SCCs can kill it if the panel is still alive , but it’s a last ditch system anyway
 
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Another thing that strikes me

A good mppt SCC will use a synchronous buck converter topology as opposed to an asynchronous one. The switching diode is replaced by a mosfet. ( the low side mosfet )

This means in a SCC over voltage situation it’s likely the low side mosfet will short and hence the resulting battery current will blow an attached fuse . This is what I suspect is gone in my lightening damaged Victron mppt.

Hence with a quality SCC, the failure mode , of allowing panel voltage to leak out , will not actually occur.
 
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Another thing that strikes me

A good mppt SCC will use a synchronous buck converter topology as opposed to an asynchronous one. The switching diode is replaced by a mosfet. ( the low side mosfet )

This means in a SCC over voltage situation it’s likely the low side mosfet will short and hence the resulting battery current will blow an attached fuse . This is what I suspect is gone in my lightening damaged Victron mppt.

Hence with a quality SCC, the failure mode , of allowing panel voltage to leak out , will not actually occur.


Well that's assuming your SCC failed because of over PV input voltage, and also assuming the failure mode of the lowside mosfet was short, and also assuming the lowside even fails at all.

Example in my case, the MPPT I had do this, granted was asynchronous but only one of the two input mosfets shorted. My controller was not exposed to any over PV voltage in any way, the mosfet just failed. So even if mine was asynchronous, the low side mosfet would have just kept doing it's thing.
 
What you guys think about using this attached over/under voltage relay connected between charger controller and battery, that command an ssr installed between pv and charger? If the charger goes caput and let pv voltage goes past it, this overvoltage relay senses it and close the circuit of the ssr that close the connection from the pv. No more tension past the ssr. Hope it make sense (I have a 48v system but there is also for 12 and 24)
 

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