Siting multiple chargers

[tonyt40]

I have been racking my brains over this for a while. I have a semi traditional with the domestic batteries in two banks of three in the engine compartment. I am just in the process of trying to tidy it up. The question is do I need to take the cabling for the solar and mains chargers independently back to the batteries or can I parallel them up and run one larger pair of cable back from the cupboard where the chargers live to the batteries.

 

Another question related to charging. If my solar is generating and my mains charger is on will they compete with each other? Does the mains charger see the bulk charge from. The solar and go straight to float or vice versa? I was thinking of installing an isolator on the panel side of the solar so when the mains is charging it can do it's job properly and go through all the stages.

 

Thanks

[Robbo]

I use a bus bar where all the connections for the batteries go and one cable to the battery, makes wiring a lot simpler.. remember you'll need to fuse the cable going to the bus bar.

 

You can reduce the ammount of fuses by using the min specced cable specced for the total amount of amps you can create, or max you can use, to all the chargers and outgoing devices.

[Keith M]

I believe the the two charging source will complete

 

The one with the higher voltage will win

 

Keith

[matty40s]

You will find that in most cases any alternator or charging unit will cause your solar controller to revert to float mode. I wouldn't bother with a separate isolator.

[Geo]

The chargers will compete and as has been said the one with the highest voltage setting will win be that alternator, mains charger or solar controller. While all the charging sources are below their trigger voltages they will work in parallel.

 

I would put an isolator switch in between the solar controller and the batteries but purely so that if you want to work on the batteries you can stop any charge/voltage coming from the solar controller to the batteries while you are working. It saves having to find light proof coverings and putting them over the panels to stop the generation while you work.

Edited December 11, 2016 by Geo

[Chewbacka]

But my (most?) MPPT controller instructions require the controller to be connected to the batteries before the panels and disconnected from the batteries AFTER the panels. So leaving the panels connected in daylight and disconnecting the controller from the battery bank is not a good idea.

If you must have a switch it should be on the panel side and rated for the voltage and DC current the panels can supply. A normal 12v switch is no good if using high voltage panels in series as you may strike an arc inside the switch if you open it in bright sunlight with low batteries - ie high panel voltage and high current. A DC arc doesn't quench like an AC arc does.

Edited December 11, 2016 by Chewbacka

[WotEver]

I would put an isolator switch in between the solar controller and the batteries but purely so that if you want to work on the batteries you can stop any charge/voltage coming from the solar controller to the batteries while you are working.

No. this is a very bad idea. Disconnecting most controllers from the battery while the panels are generating will result in the rapid release of the magic smoke from the controller.

 

But my (most?) MPPT controller instructions require the controller to be connected to the batteries before the panels and disconnected from the batteries AFTER the panels. So leaving the panels connected in daylight and disconnecting the controller from the battery bank is not a good idea.

If you must have a switch it should be on the panel side and rated for the voltage and DC current the panels can supply. A normal 12v switch is no good if using high voltage panels in series as you may strike an arc inside the switch if you open it in bright sunlight with low batteries - ie high panel voltage and high current. A DC arc doesn't quench like an AC arc does.

Exactly so.

 

Simplest thing to do is to cover the panels with a blanket or two then unplug them from the controller. Then the controller can be disconnected from the batteries if required.

[Geo]

But my (most?) MPPT controller instructions require the controller to be connected to the batteries before the panels and disconnected from the batteries AFTER the panels. So leaving the panels connected in daylight and disconnecting the controller from the battery bank is not a good idea.

If you must have a switch it should be on the panel side and rated for the voltage and DC current the panels can supply. A normal 12v switch is no good if using high voltage panels in series as you may strike an arc inside the switch if you open it in bright sunlight with low batteries - ie high panel voltage and high current. A DC arc doesn't quench like an AC arc does.

 

I have no problem with that, but it does mean that even to change the batteries there is a danger of damage to the controller. That to me is bad design. Just so long as the power from the solar does not reach the battery.

 

Disconnecting the battery and leaving the panels connected does not upset my solar controllers, Morning Star

Edited December 11, 2016 by Geo

[WotEver]

 

Disconnecting the battery and leaving the panels connected does not upset my solar controllers, Morning Star

Good for you.

 

It does affect other controllers however.

[Chewbacka]

 

I have no problem with that, but it does mean that even to change the batteries there is a danger of damage to the controller. That to me is bad design. Just so long as the power from the solar does not reach the battery.

 

Disconnecting the battery and leaving the panels connected does not upset my solar controllers, Morning Star

I was warned - don't remember where, but it is plausible - if you have an auto 12/24V controller, then connecting the solar panels first, the controller is powered up and does not then know if the battery bank is 12 or 24V. It may then assume 24v which when you connect it to your batteries is going to give them too much voltage.

 

I find it always best when giving advice to err on the side of caution as I have no idea if the op has a controller that is happy if the battery bank is disconnected/connected when the panels are live and I would be most upset if my advice caused damage or harm.

[nicknorman]

I have been racking my brains over this for a while. I have a semi traditional with the domestic batteries in two banks of three in the engine compartment. I am just in the process of trying to tidy it up. The question is do I need to take the cabling for the solar and mains chargers independently back to the batteries or can I parallel them up and run one larger pair of cable back from the cupboard where the chargers live to the batteries.

Another question related to charging. If my solar is generating and my mains charger is on will they compete with each other? Does the mains charger see the bulk charge from. The solar and go straight to float or vice versa? I was thinking of installing an isolator on the panel side of the solar so when the mains is charging it can do it's job properly and go through all the stages.

Thanks

You will find a lot of BS spoken about mixing charging sources but it is just that - BS. I have two charging sources when we are cruising, the alternator and the Combi fed from the travelpower. They play nicely together. It will help if the process a bit if they are set to similar voltages but regardless, when the batteries can take plenty of current (low state of charge) they will both contribute to charging. Once the battery demand decreases it may be that one device goes to float before the other, but that makes absolutely no difference to the overall charging time. If you put in an isolator to say eliminate the solar, that will just result in slightly longer charging times since the solar won't be able to contribute during the early part of the charging.

 

Oh and any advice to isolate the controller from the batteries is exceptionally bad advice and may well fry your controller if the sun is out. If you really want to put an isolator anywhere, put it between the panels and the controller. On the very rare occasion that you want to isolate the controller, turn the panel isolator off first then remove the fuse between batteries and controller.

 

Getting back to your original question it should be fine provided the wire is adequately thick to avoid excessive voltage drop when the solar and charger are both supplying current. Make sure the fuse can cope with the combined current and if it can't, this may be because the cable can't either!

Edited December 11, 2016 by nicknorman

[tonyt40]

You will find a lot of BS spoken about mixing charging sources but it is just that - BS. I have two charging sources when we are cruising, the alternator and the Combi fed from the travelpower. They play nicely together. It will help if the process a bit if they are set to similar voltages but regardless, when the batteries can take plenty of current (low state of charge) they will both contribute to charging. Once the battery demand decreases it may be that one device goes to float before the other, but that makes absolutely no difference to the overall charging time. If you put in an isolator to say eliminate the solar, that will just result in slightly longer charging times since the solar won't be able to contribute during the early part of the charging.

Oh and any advice to isolate the controller from the batteries is exceptionally bad advice and may well fry your controller if the sun is out. If you really want to put an isolator anywhere, put it between the panels and the controller. On the very rare occasion that you want to isolate the controller, turn the panel isolator off first then remove the fuse between batteries and controller.

Getting back to your original question it should be fine provided the wire is adequately thick to avoid excessive voltage drop when the solar and charger are both supplying current. Make sure the fuse can cope with the combined current and if it can't, this may be because the cable can't either!

I'm going to take a pair of 25mm2 cables from the battery isolator via a 125a fuse to the electric cupboard (about 2m). Think I will then fit a secondary accessible isolator for the domestic that I can actually get to but loop off the battery side to two fuses to connect the solar and mains chargers - that way I can isolate the domestic when I leave it but leave the chargers on. The inverter is on a dedicated supply from the batteries via its own isolator and fuse

 

If I fit an isolator in the solar it will be between the controller and the panels (as per domestic systems) but will look at this later.

 

Thanks guys. Just need the cable and crimps to arrive now.

[WotEver]

I'm going to take a pair of 25mm2 cables from the battery isolator via a 125a fuse to the electric cupboard (about 2m). Think I will then fit a secondary accessible isolator for the domestic that I can actually get to but loop off the battery side to two fuses to connect the solar and mains chargers - that way I can isolate the domestic when I leave it but leave the chargers on. The inverter is on a dedicated supply from the batteries via its own isolator and fuse

 

If I fit an isolator in the solar it will be between the controller and the panels (as per domestic systems) but will look at this later.

 

Thanks guys. Just need the cable and crimps to arrive now.

That all sounds excellent although the 25mm sounds somewhat as if it might be on the small side. What's your total domestic load and what sizes are the mains and solar chargers?

[tonyt40]

Chargers are solar 30a and mains 50a. Total domestic load is about 80a but this was before lights were changed to led with everything on and no diversity allowed. I based the calculation on 50a at 3‰ volt drop I checked some cable tables and 25mm2 fitted the bill.

 

It's currently on a run of about 3m fed from 10mm (not my wiring)!!

[WotEver]

I guess 3% drop isn't going to hurt too much

 

Seeing as you hopefully won't be doing it again then you could consider going larger if you wanted to...

[tonyt40]

According to the calculation it's only just at 3‰ at 95a. At 50a ( only expecting it to be about 30a unless I take to showering in the dark with all the lights on inside and out and charging everything I own simultaneously ) it's about 1.5%. I think it will be fine at that. There is no point over engineering it for the sake of it in my opinion.

[WotEver]

At 50A you'd drop just 0.144V so yeah, it's fine

[Geo]

I was warned - don't remember where, but it is plausible - if you have an auto 12/24V controller, then connecting the solar panels first, the controller is powered up and does not then know if the battery bank is 12 or 24V. It may then assume 24v which when you connect it to your batteries is going to give them too much voltage.

 

I find it always best when giving advice to err on the side of caution as I have no idea if the op has a controller that is happy if the battery bank is disconnected/connected when the panels are live and I would be most upset if my advice caused damage or harm.

 

As I said earlier it is bad design and probably cost saving, thus people buy them. The Morning Star is voltage sensing up to 48V from memory.

[Chewbacka]

 

As I said earlier it is bad design and probably cost saving, thus people buy them. The Morning Star is voltage sensing up to 48V from memory.

If you accept that people buy them, then you should check what they have bought before giving advice that could damage equipment or at least make clear the assumptions and limitations of the advice given. It is possible that you did not know that many controllers must be battery connect first, disconnect last, in which case it is understandable that you gave unwise advice, but you have not said that.