Solar panels

[alexmh1985]

Hi guys, I've invested in a 400w solar panel and a victron mppt smart controller. Just a quick question for the electrical wizards, it came with 2 125v dc breakers, a c25 one and a c63 one, I take it the breaker goes in between the mppt and the battery bank but which one do I use? I have 960ah battery bank. Do I need to connect the mppt directly to the batteries or is it ok connecting it after the battery isolator, would it damage something if the battery isolator was in the off position??

[ditchcrawler]

1 minute ago, alexmh1985 said:

Hi guys, I've invested in a 400w solar panel and a victron mppt smart controller. Just a quick question for the electrical wizards, it came with 2 125v dc breakers, a c25 one and a c63 one, I take it the breaker goes in between the mppt and the battery bank but which one do I use? I have 960ah battery bank. Do I need to connect the mppt directly to the batteries or is it ok connecting it after the battery isolator, would it damage something if the battery isolator was in the off position??

I would suggest you connect direct to the battery via one of the breakers supplied, The breaker needs to be at the battery end of the cable, not the controller end 

[WotEver]

Put the 25A one between panel and controller. Put the 63A one between controller and battery. Use 10mm² cable between controller and battery. Connect the controller to the battery before you connect the panel to the controller. 

23 minutes ago, alexmh1985 said:

is it ok connecting it after the battery isolator, would it damage something if the battery isolator was in the off position??

No and yes in that order. 

 

If you don’t want to use 10mm² cable then use the smaller breaker between controller and battery and don’t have one between the panels and controller. 

Edited July 21, 2019 by WotEver
Typo

[Sea Dog]

1 hour ago, WotEver said:

 

 

If you don’t want to use 10mm² cable then get over yerself and buy some, it's not exactly dear. It will minimise the volts drop between the controller and your batteries and allow you to get the best out of your solar. You can also then do the right thing with the breakers.

Fixed that for you Tony!

 

[Tony Brooks]

I will repeat what I said on a similar previous thread.

 

I would never fit a circuit breaker that can be manually tripped easily between the batteries and controller but would fit a suitably rated old fashioned fuse.  The reason is the majority of controller manufacturers, if not all, are very clear that the batteries must never be disconnected from the controller while the panels are connected. With a manually tripped breaker that is all too easy to do. I think this is to do with auto-sensing 12V of 24V and I think we had someone with twin controllers who was getting a very high solar charge. I put this down to the controller setting itself for a 24 volt bank when the battery was disconnected.

 

If you do fit the breaker just make sure it is impossible or very difficult to manually trip and place a warning sign by or over it.

 

[WotEver]

2 hours ago, Tony Brooks said:

If you do fit the breaker just make sure it is impossible or very difficult to manually trip and place a warning sign by or over it.

Yup, good advice. The only reason I suggested fitting the MCB was because he’s been given it for free as part of the kit. 

[alan_fincher]

OK, so ancillary question......

 

We have been using a single loaned panel, and this has been our first experience of any solar at all.

 

I bought a VERY basic controller, (about £14!), just so we had something - currently it is "lashed up" but not a good permanent installation.

If I'm understanding correctly, then the panel should never be connected to the controller, unless the controller is already connected to the batteries.  I assume the controller is at risk if you have a panel connected to it, but not joined to the batteries.

If we decide to go with our own panels, and a proper installation, I don't wish to be in a situation where the controller is permanently connected to the batteries, if I'm not making use of any panel(s), but if I introduce any way of isolating the controller from the battery bank, I risk that being activated whilst panels are feeding the controller.

 

How is it best to handle that?  Perhaps a two pole switch that breaks both the connection to the battery bank and that to the panels at the same time?   But would there be any risk that the battery actually got disconnected milliseconds before the panel(s) were, and if so could that be enough to damage the controller, please?

[Richard10002]

Oh dear! I have a breaker between panels and controller, (which obviously isnt necessary, but is convenient  from time to time).

 

I have never thought twice about turning off the battery isolators if working on the batteries, or associated wiring, (or whatever), and have never disconnected the panels before doing so. It hasn't caused a problem so far, but I'll try and remember to trip the panels breaker in future.

 

Having said that, I'm recalling from reading the Tracer manual when fitting that it may not have been something that was mentioned as an issue ???

[Tony Brooks]

First of all as far as I can tell (no definitive statement I have found on this) The reason you must never connect the panels with the controller is the controller is auto sensing and as the panels will produce over 20 volts when in sun and open circuit it could well decide its on a 24 volt battery bank and proceed to regulate the charge for that. I very much doubt the controller will be dam,aged unless you have a huge array connected in series bur you may well destroy your battery bank by over voltage charging when the bank is well charged.

 

I have no idea why you would not want to have the panels permanently connected. On  reputable controllers the charge will drop to float voltage and then periodically do a short "semi-equalisation" charge. Any problems having two or more sources of charge connected are very minor and easily  dealt with. The biggest "problem" is that will fully charged batteries the alternator might shut down and beep at you. Ditto a battery charger but note the fully charged batteries bit. Well nearly fully charged and by that time it will not matter what shuts itself down and you will still have some charge. I suspect the best way is an extra double pole switch with one pole isolating the batteries and one the panels but it is, in my view, needlessly complicated and builds in another point of unreliability Maybe Mrs Alan could knit a thick cover for the panels when they are not wanted so they do not produce any output and the controller thinks it is night..

[David Mack]

56 minutes ago, Richard10002 said:

 

I have never thought twice about turning off the battery isolators if working on the batteries, or associated wiring, (or whatever), and have never disconnected the panels before doing so. It hasn't caused a problem so far, but I'll try and remember to trip the panels breaker in future.

 

Turning off the battery breaker may be fine, but what happens when you turn it back on? I thought you should disconnect or cover the panels first, or switch back on at night.

[Chewbacka]

1 hour ago, David Mack said:

 

Turning off the battery breaker may be fine, but what happens when you turn it back on? I thought you should disconnect or cover the panels first, or switch back on at night.

With some controllers if you leave it connected to the panels and reconnect to the batteries in sunlight then the controller may decide it is connected to a 24v battery and attempt to charge it to 24v, on the other hand it may not.  Worth the risk???

So I do what you do.

Edited July 21, 2019 by Chewbacka

[WotEver]

3 hours ago, alan_fincher said:

If we decide to go with our own panels, and a proper installation, I don't wish to be in a situation where the controller is permanently connected to the batteries, if I'm not making use of any panel(s)

Why?

[matty40s]

3 hours ago, alan_fincher said:

OK, so ancillary question......

 

We have been using a single loaned panel, and this has been our first experience of any solar at all.

 

I bought a VERY basic controller, (about £14!), just so we had something - currently it is "lashed up" but not a good permanent installation.

If I'm understanding correctly, then the panel should never be connected to the controller, unless the controller is already connected to the batteries.  I assume the controller is at risk if you have a panel connected to it, but not joined to the batteries.

If we decide to go with our own panels, and a proper installation, I don't wish to be in a situation where the controller is permanently connected to the batteries, if I'm not making use of any panel(s), but if I introduce any way of isolating the controller from the battery bank, I risk that being activated whilst panels are feeding 

In your situation Alan, the panel is a nominal base voltage of 12v, as are your batteries, so it woildnt really matter which was connected or disconnected first.

The rule for connection only really comes in to play when you have single panel base voltages of 24, 36 or 48v, or you have 12v panels connected in series, which will take you up the higher nominal voltages when combined.

Using 12v panels in parallel will not give you this problem.

 

The only thing to remember is the controller will work at the first nominal voltage it senses. So if you first connect panels which are at 24v or higher, connecting the controller to a 12v bank will fry the bank.

 

You can leave a controller connected to your batteries for ever without fitting panels, it will just sit there and do nowt. 

You can connect panels to your controller and its heat sink will take care of any generation heat, ....the big question is why you would want to do that and not be charging your batteries.

 

[Tony Brooks]

Matty - are you sure about that. Mt panels have an open circuit voltage of 21 volts and 21 volts is closer to 24V than 12V is. How does the said controller know it is connected to a 12V battery bank and not a very discharged 24 volt one? I get the impression things like this work to a range of voltage so (say) 10V to 16V = 12V bank and 20V to controller max = 24 volts bank.

 

Not saying you are wrong, just asking.

[Alan de Enfield]

1 hour ago, Tony Brooks said:

Matty - are you sure about that. Mt panels have an open circuit voltage of 21 volts and 21 volts is closer to 24V than 12V is. How does the said controller know it is connected to a 12V battery bank and not a very discharged 24 volt one? I get the impression things like this work to a range of voltage so (say) 10V to 16V = 12V bank and 20V to controller max = 24 volts bank.

 

Not saying you are wrong, just asking.

It must know somehow or it would be squirting  up to 120v (ish) into my batteries

 

 

 

Edited July 22, 2019 by Alan de Enfield

[Onewheeler]

1 hour ago, Tony Brooks said:

Matty - are you sure about that. Mt panels have an open circuit voltage of 21 volts and 21 volts is closer to 24V than 12V is. How does the said controller know it is connected to a 12V battery bank and not a very discharged 24 volt one? I get the impression things like this work to a range of voltage so (say) 10V to 16V = 12V bank and 20V to controller max = 24 volts bank.

 

Not saying you are wrong, just asking.

I'd have thought a 400 w panel would have a terminal voltage if over 30 V.

[Tony Brooks]

1 minute ago, Onewheeler said:

I'd have thought a 400 w panel would have a terminal voltage if over 30 V.

It depends upon the design. Domestic ones certainly but nominal 12V ones maybe not. In any case this just tends to confirm my suspicions.

 

[ditchcrawler]

Truth is we dont know with the amount of information supplied and everyone is speculating

[matty40s]

1 hour ago, Tony Brooks said:

Matty - are you sure about that. Mt panels have an open circuit voltage of 21 volts and 21 volts is closer to 24V than 12V is. How does the said controller know it is connected to a 12V battery bank and not a very discharged 24 volt one? I get the impression things like this work to a range of voltage so (say) 10V to 16V = 12V bank and 20V to controller max = 24 volts bank.

 

Not saying you are wrong, just asking.

The  controller might sense something approaching 24v from a 12v panel as an absolute maximum on a cold bright spring morning,  however, switching itself to 24v operation and trying to get the required 28-35v to put charge in the batteries would be a fruitless task.

Controllers also have a failsafe minimum battery bank charging level so wouldn't put charge into a 24v bank sitting at 21v.

 

[Richard10002]

15 hours ago, David Mack said:

 

Turning off the battery breaker may be fine, but what happens when you turn it back on? I thought you should disconnect or cover the panels first, or switch back on at night.

Never gave it a moment of thought..... turned off the batteries at the isolator/s; worked on the batteries, (or whatever); turned back on at the isolators; all fine with the solar and controller. All in the same daylight on the same day.

[WotEver]

2 hours ago, matty40s said:

The  controller might sense something approaching 24v from a 12v panel as an absolute maximum on a cold bright spring morning

But that’s irrelevant. You can feed any voltage into a controller up to its maximum and it won’t affect the output. The controller determines what voltage the bank is from the voltage that it sees on its output, not its input. Are you suggesting that 120V from series panels would convince the controller that it’s charging a 120V battery?

1 minute ago, Richard10002 said:

Never gave it a moment of thought..... turned off the batteries at the isolator/s; worked on the batteries, (or whatever); turned back on at the isolators; all fine with the solar and controller. All in the same daylight on the same day.

Three possibilities...

 

1. The controller is a fixed 12V device. 

2. The batteries were at a low state of charge. 

3. You were lucky. 

[Richard10002]

15 minutes ago, WotEver said:

Three possibilities...

 

1. The controller is a fixed 12V device. 

2. The batteries were at a low state of charge. 

3. You were lucky. 

1 - no, Tracer 4215BN, senses 12V / 24V DC

2 - unlikely. When working on batteries it is usually to check Specific Gravity, so they would be full, or close.

3 - I have been lucky every time, (more than 4 or 5 times).... and I'm not that lucky  

 

or, possibly, having read the manual for the controller and remote display:

 

4. In the MT50 remote meter, it is set to Rated Voltage = 12V, (with over voltage disconnect = 16V) - I cant tell whether the Rated Voltage can be changed, but presume there are some choices - might have a play later when batteries are full.

 

Presumably this setting tells the controller that the battery bank it is connected to is 12V and, if the voltage goes above 16V, it should disconnect from the batteries?

 

Hope that makes sense

[WotEver]

3 minutes ago, Richard10002 said:

In the MT50 remote meter, it is set to Rated Voltage = 12V, (with over voltage disconnect = 16V) - I cant tell whether the Rated Voltage can be changed, but presume there are some choices - might have a play later when batteries are full.

 

Presumably this setting tells the controller that the battery bank it is connected to is 12V and, if the voltage goes above 16V, it should disconnect from the batteries?

Yep, that makes sense. So it’s like 1b from my list

 

If the controller ‘knows’ that the bank is 12V then it’s not going to try charging it as a 24V bank. I wonder how it knows and under what circumstances that persists?

[matty40s]

1 hour ago, WotEver said:

. Are you suggesting that 120V from series panels would convince the controller that it’s charging a 120V battery?

 

Absolutely not, I was referring to Alan Finchers simple current set up involving 1 x 100w 12v panel and his 12v battery bank.

[WotEver]

36 minutes ago, matty40s said:

Absolutely not, I was referring to Alan Finchers simple current set up involving 1 x 100w 12v panel and his 12v battery bank.

But he has a controller in between.