SBMS - Solar BMS from electrodacus

[T1 Terry]

I dont quite understand though, Are you saying the infeed should retain a volt or so above the battery -to what point? OK so its +1 at each panel, then +1 at the joiner or busbar, -at what point would it be the same as the battery voltage? Right on the battery, at the relay (in boost)? Could you elaborate?

The voltage at the terminals on the back of the solar panel is the charging source voltage. You are looking for the total voltage drop from the source to the battery for each solar panel. If you find all of them higher than 1v above battery voltage, chances are the problem is between the junction box and the battery terminals, so check each position the cable connects from the junction box all the way back to the battery between the positive and negative at that length away from the battery. The point where the voltage changes drastically will show the area where the problem is, between the point where the voltage was high and the point where it was close to the battery voltage. It could be in the negative or positive cable or even a connection or a cable crimp.

Alternatively, if you find only a few of them high, then check between the solar panel and the junction block and see if the big voltage difference is some where along those cables.

T1 Terry

[T1 Terry]

Be wary of stainless though, copper is a much better choice IMHO, the bolt will be doing all the electrical work with a stainless washer

Don't try to pass current through a stainless bolt, the resistance is high through a stainless bolt and will cause voltage drop. The idea is to use the flat surfaces provided by the stainless washers to apply even pressure between the electrical contact surfaces and this is where the electrical current should pass, the bolt and washers are only there to provide the clamping pressure. This is why it is so important to have clean contact faces between the terminals, any resistance at this point will create heat and that heat will be transmitted along the copper cable. Just running you hand along the cable can help to locate a bad connection because it will get hotter the closer you get the bad joint. Take that as a warning and don't put you finger on the bolt, you will end up with the raised writing on the head of the bolt branded into your finger tip .... and it takes a few weeks before you get anything but pain every time you touch something with the branded finger tip If the bolt looks blue or the cabling darker near the joint, be careful.

T1 Terry

[Peter and Sandra]

Bruce
I suspect the problem with MC4 connectors and vehicles is that while travelling the wiring is subject to a constant wind velocity which moves things ever so slightly even when they are well strapped down, the only ones that I considered to be still ok were the two where I had sikaflexed both sides of the cables to the roof effectively immobilising those particular connectors.
The problem is probably compounded by the fact that most motorhome and caravan installations are usually 12v so the current is far higher than large residential systems that run at 100's of volts in that any poor connections are going to be heated by the higher currents.
This is only my theory that what may have caused the problem in my setup.
Would be interesting to know how the MC4 connectors go on the NW corner of Tassie where the wind never stops.
I forgot to take pics of the obviously melted MC4's before I binned them, a few others that while they weren't obviously melted did break the plastic "snouts" off when unplugged probably due to the plastic getting brittle from being heated by the poor connection.

[BernieQ2]

I have had MC4's on 4 motorhomes without any problem . My house also uses them on the solar .
I spent 7 months last year in Tassie also with no problems . They have been on the (now not ours) motorhome for 5 years .
And when I put the two new panels (250w each) on the van they also will have MC4 connectors .
Bernie .

[T1 Terry]

part of the demo we are doing for Stone The Crows has a pr of MC4 connectors cut in half to show how far the pins go into each other, the female socket is also cut away so you can see the copper piece that makes the contact with the male pin.
The most common thing is this copper piece is either pushed deep into the female socket so the pin doesn't locate with it, or it isn't there at all. No way of knowing if you have this problem or not, the pins and sockets don't come all the way to the end of the plastic housing so you can't actually look inside the socket nor can you be sure the pin didn't push this copper connector deeper into the socket and no longer makes a good contact.
We actually take the pin and socket out of the plastic bit, slip a piece of heat shrink over cable, plug the pin into the socket, heat it with a hot air gun on full noise and melt solder into the join, let it cool till it can be touched without pain, then slip the heat shrink over and heat that with the hot air on the lower setting, connection complete and you can be confident that joint is good.

We have had cables not connected in the back of the MC4 connector, looked to have been twisted off when the cap was tightened, lots where the pin wasn't secured in the plastic holder so it pushed through rather than pushing into the socket, and some where the pin or socket was deformed so it was more likely the pin or socket would be pushed out of the plastic holder rather than engaging with each other. Of course there is the other thing regarding standards, there are so many variations on an MC4 connector it is not always guaranteed the female and male with plug into each other.

T1 Terry

[Barboots]

My understanding is that the paired MC4s must be identical. I'm reasonably sure I read that this is a requirement under AS for grid connected systems.

I imagine it's very tempting to leave the ones on the panel...

Cheers, Steve

[T1 Terry]

My understanding is that the paired MC4s must be identical. I'm reasonably sure I read that this is a requirement under AS for grid connected systems.

I imagine it's very tempting to leave the ones on the panel...

Cheers, Steve

I've seen that many different MC4 connectors on grid tie suitable panels it tells m there is no real standard for even those applications. The stuff for extra low voltage has no regulations at all because it doesn't require a licenced installer, as long as the voltage remains below 120vdc with a max of 5% ripple. I have seen MPPT controllers with a max open circuit voltage of 150vdc, but that is above the legal voltage for a DIY install, so keeping the series string below the 120vdc open circuit would be a sensible idea. 3 of the Tindo grid connect suitable 270w panels has an open circuit voltage of 115.5v and a Vmp of 90vdc and can push out 15 amps at that voltage. The MC4 connectors are not those fancy ones with the flip over cap on each that lock them together, they look much the same as any other MC4 connector.
The differences come with 1 or 2""O" rings, a round snout of the male plastic plug that has the female pin/socket inside (a hermaphrodite?) or semi round with flats each side, large diameter or small diameter hole in the female plastic plug with the male pin inside (self satisfying unit), the recess for the "O" ring is either deep for the dual "O" ring mate or shallow designed for the single "O" ring type, and sometimes the plastic locking clips don't match up either. The sure thing was to either cut the whole thing off and join them via a different method, or knock the pins out as described earlier. The pin and heat shrink idea makes it easy to feed the cables through conduit etc ...

T1 Terry