For all those using the Microcare MPPT’s. No need to worry about damaging your controller when your LFP battery suddenly turns off under full sunlight. Microcare have developed this high voltage protection board that fits inside the controller. It is quite simple to install and gives that extra peace of mind. 

I know that used to be a problem for them in the past. The MPPT would blow up if the battery disconnected suddenly. I suspect this protection board is just a voltage clamp. Nothing wrong with that, simple is good!

It may protect the MPPT, but if it still allows the open circuit PV voltage to appear at the battery terminals then it won't protect anything else and your expensive inverter will go boom.

@Solaris can you give more info maybe about the unit. Does it cut solar side of the input of the mppt or the battery side. If it's from the solar input side and it cuts the solar, then i think it can work. What do you think @plonkster and @Stanley ? 

I'm not sure what it actually does. I can't read the labels on those screw terminals in the picture either. I guess that if it switches the PV off very quickly, even if that just means turning off the FETs / IGBTs that make up the buck converter (although I don't know why they would need a separate PCB for that) then it could help. If it just clamps the voltage to the power supply on their controller then it will just protect the MPPT.

My guess was that it connects to the battery terminals and clamps the voltage to something non-blowing-uppy... like 65V. But now I am not so sure anymore.

It would depend on how you connect it, from that one can probably figure it out. Also, that ribon cable looks suspiciously like one of the two ribbon cables inside (one connects the battery voltage to the internal control board (SMPS to 12V, 7805 to 5V pipeline), the other connects the output of the high voltage isolated stage and PWM control to the opto/FET on the lower board.

Maybe this just goes on the input side of the control board and just prevents the SMPS from getting a high input voltage.

Edited June 26, 20205 yr by plonkster

I'm pretty certain that it's too small to absorb enough energy to clamp the voltage at the battery terminals to something safe when subjected to several kW of PV panels with a Voc of 150V or so. Unless it only needs to do that for a couple of mS before the MPPT realises the problem and switches off. (Even then it would potentially need to absorb quite a bit of energy, so I'm skeptical)

As a side note lots of MPPTs have this problem, they react too slowly when a battery is disconnected and blow up themselves and/or other equipment, and I don't know why this wasn't considered during the design stage, it's really not that hard to work around with proper hardware and software design. Assuming the MPPT is just a buck converter, then the worst case is if it is running at it's max. rated current when the battery trips. Then the voltage on the MPPTs own output terminals will start climbing pretty linearly (since the current through the inductor will remain pretty constant over a short time and the MPPT should have output capacitors, so the voltage on the output capacitors will climb at a rate determined by dv/dt = I/C). Size the output capacitors correctly so that you have a little bit of time to react, and choose a good sampling rate for your voltage measurement (or add a hardware comparator) and just turn off the PWM when the output voltage goes above some threshold.

I know lead acid batteries couldn't 'trip' like Lithium ones do, but I know of a few cases where equipment has blown up because of loose battery connections or a customer opening a battery fuse (to shut the system down) before opening the PV fuses.

 

44 minutes ago, Stanley said:

Unless it only needs to do that for a couple of mS before the MPPT realises the problem and switches off

That's what I was thinking.

45 minutes ago, Stanley said:

I know lead acid batteries couldn't 'trip' like Lithium ones do, but I know of a few cases where equipment has blown up because of loose battery connections or a customer opening a battery fuse (to shut the system down) before opening the PV fuses.

The Microcare MPPTs aso have built-in circuit breakers on the device. A trippinb breaker, or something as stupid as a human being opening the battery side before the PV side, could well cause the same issue. So absolutely agreed with you here.

I spotted on the board a input on the left of screw downs and it looks like maybe output on the right. So i guess the wire that go's from the "trip" switch ""jip""" trip switch to the board will go via this new board and the ribbon cable maybe on the mppt board moved to the new board and then from there back to the mppt board.

I think i need to drop Walter a mail and find out. But yes, like Plokster says, that design with the two switches is a bit of simpel one. Quick way to make magic smoke. 

Edited June 26, 20205 yr by Gerlach

I am not exactly sure how it works, but here is what my 60A MPPT looks like with the board installed. This protection board is the older model, but the connection is the same. It plugs in between the green power board and the red display board. You then mount it onto the choke. 

Nice clear picture, thanks. I think it answers our question of how it works.

If I read that correctly, it says PSU_Front_End_V1R1

Which tells me that it only protects the PSU of the control card.

39 minutes ago, Solaris said:

plugs in between the green power board and the red display board

The red board is actually the control board. It has a PIC microcontroller on it (below the Hitachi 16x2 LCD) and a MAX232 for the serial port interface. It is actually mounted upside down in this application, when you remove it you'll see the layout is the other way round. The ribbon cable that's on the right (which would be top left if the board was held the right way up) is where the 48V supply enters the control board.

The lower board can be more accurately called the "power board" and on your 60A and 100A units there will  be multiple power boards (each one has its own inductor, or choke, and some large capacitors, two MOSFETS, a Schottky diode, and an opto-coupler that actually switches the main FET (small white package with 6 legs).

This protection board likely sits inline with the power supply, so I think you're right, it just interrupts the main supply if it goes too high.

The ribbon cable at (1) is where the power supply feeds into the main board. (2) is a switch mode power supply that drops the voltage to 12V. I'm not sure what (3) is, on my charger it's left out and replaced by a wire link. (4) is a 5V linear regulator that supplies the microcontroller and the rest of the board. (5) is adjustment screws for measurements (battery voltage etc). (6) is the ribbon cable that feeds the PWM signal and the 15V isolated supply to the power board(s). The isolated supply is used to switch the main FET(s) of the buck converter on the high side.

The 12V made by chip (2) also powers the cooling fan. There is a small NPN transistor close to the fan connection that switches the fan on the negative side.

4 minutes ago, plonkster said:

There is a small NPN transistor close to the fan connection that switches the fan on the negative side.

There are no temperature sensors in the case. The MCU switches the fan on under certain hard-coded conditions. I could never quite figure out exactly what they were, it didn't seem to be purely power-level related.

Hhhhmmmmmm wel, they fix that one problem if someone drop the battery side of the trip switch but still didn't fix that other problem.  

Me and TTT was busy testing settings for lifepo4 charging, so moving my balk charge from 54.6v to 56.7v. Hohooooo!!!! When the batteries got full the bms stop the charge and then mppt went like crazy. It started to ramp up the volts because it cant se the battery volts. Sounded like electrical fense igniter unit and then the safety kicks in. Over and over. Likely i was standing and watching the mppt. I immediately went back to my old settings that i know is working for more then 5 months now. I spotted it on my graphs to. TTT had the same problem, he gets errors and you can see the spike of 62v. So he started to use the same settings then me. Problem solved. 

I see Walter post n new video of there new mppts thats using a plug that connects to the mppt. I guess they running something now that connects to the dry contact in the lithium unit to inform the mppt to do stuff.

@Solaris did Microcare installed it for you or did they send you they add in board and price of it?

 

5 minutes ago, Gerlach said:

mppt went like crazy. It started to ramp up the volts because it cant se the battery volts. Sounded like electrical fense igniter unit and then the safety kicks in. Over and over. Likely i was standing and watching the mppt.

Wow, you are very lucky that nothing blew up. That could have been an expensive exercise.

8 minutes ago, Stanley said:

Wow, you are very lucky that nothing blew up. That could have been an expensive exercise.

Stanley. You can say that again!!!!! Glad i was there to keep a eye. They got mos a saying in Afrikaans " moet nie krap waar dit nie jik nie". Back to my old settings and everything works super again. I still want slap something together with a high volt dc contactor that cuts the PV side. 

I think with the second lifepo4 bank in will help with this sort of stuff if one bms drop, then second bank is there to help. Plans is to 3 Lifepo4 banks. 

5 minutes ago, Gerlach said:

did Microcare installed it for you or did they send you they add in board and price of it?

 

I bought three of these boards for my three MPPT’s while I was there for training last week. Wouter showed me how to install them. When I got home to install, I found that my 60A controller pictured above already had a protection board fitted. I fitted the other two into my two 40A controllers. It is a little cramped in the 40A controllers, but after some fighting I managed to squeeze them in. 😅
The loose boards are around R500. I suppose if they did the fitting (I guess) it would cost around R800 

22 minutes ago, Solaris said:

I bought three of these boards for my three MPPT’s while I was there for training last week. Wouter showed me how to install them. When I got home to install, I found that my 60A controller pictured above already had a protection board fitted. I fitted the other two into my two 40A controllers. It is a little cramped in the 40A controllers, but after some fighting I managed to squeeze them in. 😅
The loose boards are around R500. I suppose if they did the fitting (I guess) it would cost around R800 

Hhhmmmm guess what i will be doing today. Got a second 60a mppt the other day. So i need to check this one to see if something like this is in there. My setsolar one don't have one and still got the old Pic software on so no data on the serial side. Then i got a 3de one that i need to send in. It's dead, got it like that. Open it and tested and there is 12v power but the screen don't switch on, but funny thing. I spotted this now with the photo plonkster marked out. Mine got linear voltage regulator nummer 4  but not number 5 like yours. Hhhhmmmm. 

I need to send this mppt in so that they can replace the board under the screen. Spoke to Wouter last year about it. 

13 minutes ago, Gerlach said:

Mine got linear voltage regulator nummer 4  but not number 5 like yours. Hhhhmmmm. 

My guess is that the SMPS is a new development. They used something else in older designs (could it be that they had a whole chain of linear regulators?), so when the design was improved there was no need for one of them and it got replaced by a link of wire.

In one of my first on/off solar chargers that I built in high shool, I also had to drop the +-46V peak of a 36V bank to something usable (12V in my case). Now most linear regulators are nowhere near that, the LM317 got closest at around 40V, and the 7812 could only take 35V. There was no cheap SMPS back in those days.

So what I did was to daisy-chain to 7812s, but I raised the ground pin of the first one by an offset. I think I used a 18V Zener diode, so the max input was now 35+18V. The first 7812 would then spit out 12+18V = 30V, which was low enough for the second one.

Of course this is horribly inefficient, and you could not mount them on the same heatsink, but for low power levels it's just fine.

The reason I doubt this explanation in this case, is because the 12V fan is not exactly low-power. The rest might qualify though. That kind of setup would of course raise the consumption of the MPPT itself. With the SMPS it has a very respectable draw of 50ma or so... if I recall.

7 minutes ago, plonkster said:

So what I did was to daisy-chain to 7812s, but I raised the ground pin of the first one by an offset. I think I used a 18V Zener diode, so the max input was now 35+18V. The first 7812 would then spit out 12+18V = 30V, which was low enough for the second one.

Quite clever.

When I need a quick linear regulator that can handle a high input voltage I usually use a NPN transistor in an open emitter configuration with a Zener on the base. Works really well. Only needs 3 components (Resistor, Zener and Transistor) and can be scaled up by using a bigger transistor.

33 minutes ago, Gerlach said:

Hhhmmmm guess what i will be doing today

Looks like I’ve awoken something in you... 

Funny how one discussion brings out all those old projects we abandoned. 😁

5 minutes ago, Stanley said:

usually use a NPN transistor in an open emitter configuration with a Zener on the base. Works really well. Only needs 3 components (Resistor, Zener and Transistor) and can be scaled up by using a bigger transistor.

If the power is low enough you can just put a Zener in series with the input to the linear regulator. I did that too a few times, but then you're talking low tens of milliamps 🙂

 

Just open the second one now. Check where is this one switch mode power supply. This one don't have the protection board. 

8 minutes ago, Solaris said:

Looks like I’ve awoken something in you... 

Funny how one discussion brings out all those old projects we abandoned. 😁

Hahahahahaah that part is awoken in me from the day got hold of a screwdriver. I open all the stuff to see what's going on inside. 

19 minutes ago, Gerlach said:

This one don't have the protection board.

None of the older MPPT’s will have this protection board. They only started fitting them from late 2019.  All the new controllers have them as standard with a lithium interface. 
That plug thing you saw in the video with Wouter is for the lithium communication cable. It allows charge/discharge on all the new Inverters and MPPT’s 

 

23 minutes ago, Gerlach said:

Hahahahahaah that part is awoken in me from the day got hold of a screwdriver. I open all the stuff to see what's going on inside.

I am exactly the same. 🤭

 

1 hour ago, Gerlach said:

I still want slap something together with a high volt dc contactor that cuts the PV side. 

I had this very same idea before these protection cards came along. My idea was to use a 48v relay that would open (cutting power from the PV to the MPPT) as soon as the battery disconnected. I went so far as to do it with a solid state relay. It worked for about 20 mins, it got so hot I couldn’t touch it and then burned out. 😩 
I then learned that solid state relays are not designed for constant use.

My next idea was to use a 48v golf cart relay. I found some, but when I heard that they were about R1500 each I hesitated.