Location of battery cut off switch with solar panels. Small boat Hunter Minstrel.

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bremar

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I have 2 solar panels feeding through a controller to a 100 a/h battery. There is the standard'ish large red manual cut off switch that cuts off the battery from everything. I have no engine charging and only this one battery for navigation lights,navigation equipment,interior lighting and power generally.
When I leave the boat on its swinging mooring I always have a debate with myself as to whether to switch it off or not because the solar panels will not be able to charge the battery if I do.
I have read through nearly all the posts on solar panels in this forum but none seem to directly address the best way of tackling the location in the wiring of a battery cut off switch.
Subject to any observations you chaps may have I think I want to bypass the battery cut of switch so that the solar panels feed directly to the battery, that way charging continues while I'm away and I can switch of the other electrics. BUT:
1. What safety precautions should I take? I don't want to worry about the wiring shorting and causing a fire etc. And
2. I appreciate that there is a "load" take of point on the solar panel controller , which would still be available if the solar panels were connected directly to the battery and I used the battery cut off switch to disconnect the rest of the electrics but I'm not sure if there's a need for me to use this to power anything if I'm away from the boat?

Than you in advance
Bremar.
 
Good idea and easy enough to do. Connect solar panel directly to the battery positive or to the terminal on the switch that is connected to the battery, whichever is most convenient. Fit an inline fuse as close to the connection as practicable, i'd go for a blade fuse. As for the load connection, there is no need to use this if you don't have anything you want to leave on. If you have an automatic bilge pump you might want to consider where that is connected.
 
I have my panels connected in this way. the only thing id add is that you need a solar controller that stops charge at 13.8v or slightly lower. With the unable to maintain type batteries ie sealed it will still gas off the water.

Maurice
 
MAURICE said:
I have my panels connected in this way. the only thing id add is that you need a solar controller that stops charge at 13.8v or slightly lower. With the unable to maintain type batteries ie sealed it will still gas off the water.

Maurice
Click to expand...

If it stops charging at 13.8V or lower the batteries will never fully charge. Modern alternators output 14.4/14.6 V and don't boil the batteries. Best bet is a decent MPPT controller that offers three stage charging and configurable charging patterns for different battery types, such as Victron etc.
 
My 125 watts of panels controlled by a PWM regulator by Sunworks are connected directly to the batteries via fuses. This has been the arrangement for many years, works perfectly well. The 1-2-both switch is bypassed by the solar wiring.
 
PaulRainbow said:
Good idea and easy enough to do. Connect solar panel directly to the battery positive or to the terminal on the switch that is connected to the battery, whichever is most convenient. Fit an inline fuse as close to the connection as practicable, i'd go for a blade fuse. As for the load connection, there is no need to use this if you don't have anything you want to leave on. If you have an automatic bilge pump you might want to consider where that is connected.
Click to expand...

That is what I have on my similar sized boat. Solar panel through fuse direct to battery terminals. Isolator external to battery box.

10W solar panel. No controller.
 
MAURICE said:
you need a solar controller that stops charge at 13.8v or slightly lower. With the unable to maintain type batteries ie sealed it will still gas off the water.
Click to expand...

As PaulRainbow wrote, 13.8V is very conservative and inefficient, although to a degree it will depend on the type of battery, and size of solar bank. Many modern alternators are regulated to peak at around 14.4V, and I haven't heard of a plague of boiled car batteries. Lead-calcium batteries are also less prone to water loss (and self-discharge) than lead-antimony, although the latter are still preferred for deep-cycle duties. Many sealed batteries are also fitted with recombiners, which (up to a point) convert the H and O back into water.
 
OP here.
Thank you for the replies so far. I think I know roughly where I'm going.
It's only a 100 amphr battery and total of 45 watts solar panels. The controler is a simple PWM controller.
1. Do all controllers allow you to adjust the cut off voltage? The instructions and controler are on the boat and I am not. But I don't recall reading about an option to adjust the cut off voltage? However presuming there is a facility What voltage? 18.8v as suggested by one poster or higher (if so what) voltage.
2. One other question what size fuse between solar panel and battery. 45watts/12 volts is approx 4amps. So do I use a say 5amp blade fuse or under a constant feed of 4amps on a sunny day will that just give break down??
3. Finally I don't mind concidering a more efficient/expensive MPPT controller, but I thought they needed solar panels fitted in series to produce a higher voltage (Ie 24 volts to maintained a sufficient voltage above 12 volts? To let it charge the battery??) tho I'm not really sure I know what I'm saying here? So an MPPT controler is a none starter for my setup?
Thanks
Bremar.
 
bremar said:
1. Do all controllers allow you to adjust the cut off voltage? The instructions and controler are on the boat and I am not. But I don't recall reading about an option to adjust the cut off voltage? However presuming there is a facility What voltage? 18.8v as suggested by one poster or higher (if so what) voltage.
Click to expand...

Not all will allow it. Forget 13.8 volts, that's just wrong.

2. One other question what size fuse between solar panel and battery. 45watts/12 volts is approx 4amps. So do I use a say 5amp blade fuse or under a constant feed of 4amps on a sunny day will that just give break down??
Click to expand...

The fuse is really only there to protect the wiring in this instance. In my experience fitting solar panel fuses too close the panel output results in blown fuses. I'd fit a 20A fuse.

3. Finally I don't mind concidering a more efficient/expensive MPPT controller, but I thought they needed solar panels fitted in series to produce a higher voltage (Ie 24 volts to maintained a sufficient voltage above 12 volts? To let it charge the battery??) tho I'm not really sure I know what I'm saying here? So an MPPT controler is a none starter for my setup?
Thanks
Bremar.
Click to expand...

For your simple setup i'd stick with what you have. Just wire the panel straight to the battery or isolator switch via a 20A blade fuse. Keep it simple.
 
PaulRainbow said:
Not all will allow it. Forget 13.8 volts, that's just wrong.

The fuse is really only there to protect the wiring in this instance. In my experience fitting solar panel fuses too close the panel output results in blown fuses. I'd fit a 20A fuse.

For your simple setup i'd stick with what you have. Just wire the panel straight to the battery or isolator switch via a 20A blade fuse. Keep it simple.
Click to expand...

I agree with all that ..... but a 20A fuse on a 45W panel seems a bit OTT to me. I have a 40W panel in the Med and use a 5A fuse. I'd use the same size for a 45W panel.

Richard
 
RichardS said:
I agree with all that ..... but a 20A fuse on a 45W panel seems a bit OTT to me. I have a 40W panel in the Med and use a 5A fuse. I'd use the same size for a 45W panel.

Richard
Click to expand...

It is OTT, but as it's only protecting the cable, it won't do any harm. I had a couple of fuses that were a little close to the minimum blow on one of my panels. My new controller has a 20A fuse in it, so i fitted the same at the battery end.
 
Three years ago the owner of this boat added solar panels to the bank that he already had. After installing he took the boat outside the marina and anchored, rowed ashore for lunch. Within half an hour this was the state of the boat. No fuses installed, it is believed that the wiring or the controller was unable to cope with the increased current. My solar controller is rated at 9 amps and I fitted 15 amp in-line fuses to both positive and negative leads.
1b609ad6866b578a47065ec443fc39ad_zps55fe1dde.jpg
 
vyv_cox said:
Three years ago the owner of this boat added solar panels to the bank that he already had. After installing he took the boat outside the marina and anchored, rowed ashore for lunch. Within half an hour this was the state of the boat. No fuses installed, it is believed that the wiring or the controller was unable to cope with the increased current. My solar controller is rated at 9 amps and I fitted 15 amp in-line fuses to both positive and negative leads.
1b609ad6866b578a47065ec443fc39ad_zps55fe1dde.jpg
Click to expand...

Excuse my ignorance, I'm away from the boat so not certain, but I'm pretty sure my old solar panel went to the controller (photonics panel and controller) and from there it went to the battery with crocodile clips, don't think there are any fuses. How would I add them?
 
vyv_cox said:
Three years ago the owner of this boat added solar panels to the bank that he already had. After installing he took the boat outside the marina and anchored, rowed ashore for lunch. Within half an hour this was the state of the boat. No fuses installed, it is believed that the wiring or the controller was unable to cope with the increased current. My solar controller is rated at 9 amps and I fitted 15 amp in-line fuses to both positive and negative leads.
1b609ad6866b578a47065ec443fc39ad_zps55fe1dde.jpg
Click to expand...

If the fuses are rated to cope with the max output of the panel, they won't blow, so how would they prevent this fire?
Presumably the solar controller is rated to cope with the max reasonable panel output?
The fuses are mostly needed to limit the current coming from the battery, for example when solar panel thieves cause a short.

The message from the picture though, might be solar power can be powerful enough to cause overheating and installations need to be properly thought out.
And maybe use quality electronics with thermal shutdown.
 
Just one point to the OP. 45 watts of solar will give aprox 2.5 amps max. Not 4 amps. You can confirm by looking at the max current the panels can supply and adding them. However generally the wattage of the panel relates not to 12v battery but the 20 volts open circuit voltage. good luck olewill
 
My controller feeds 2 batteries directly. I fitted inline fuse holders just in case anything did happen.
 
lw395 said:
If the fuses are rated to cope with the max output of the panel, they won't blow, so how would they prevent this fire?
Presumably the solar controller is rated to cope with the max reasonable panel output?
The fuses are mostly needed to limit the current coming from the battery, for example when solar panel thieves cause a short.

The message from the picture though, might be solar power can be powerful enough to cause overheating and installations need to be properly thought out.
And maybe use quality electronics with thermal shutdown.
Click to expand...

I only know what I was told about this particular incident. People who knew the owner said that he admitted not having fuses in the solar panel line.

One scenario might be that a wire became hot and its plastic insulation melted. The conductor inside was then able to short against something that was at earth potential, making the whole arrangement considerably more likely to catch fire. Many years ago I almost experienced something similar in a 12 volt VW camper. I removed the forward interior panels in the cab and found the PVC on the cable between the headlights like a scene from a horror movie - drooping of the cable like cobwebs. We were very fortunate that the exposed coper could not touch anything else.
 
PaulRainbow said:
If it stops charging at 13.8V or lower the batteries will never fully charge. Modern alternators output 14.4/14.6 V and don't boil the batteries. Best bet is a decent MPPT controller that offers three stage charging and configurable charging patterns for different battery types, such as Victron etc.
Click to expand...

A PWM controller, will probably charge to 100% given long enough. This is because the voltage reading is an average, whereas the output from a pwm controller is a series of pulses at the full panel voltage, hence over time, the battery state will be higher than expected going by the voltage.
 
William_H said:
Just one point to the OP. 45 watts of solar will give aprox 2.5 amps max. Not 4 amps. You can confirm by looking at the max current the panels can supply and adding them. However generally the wattage of the panel relates not to 12v battery but the 20 volts open circuit voltage. good luck olewill
Click to expand...

Also remember that a 4amp fuse does not instantly blow at 4amps - it may take a few minutes to an hour so beware fitting over rated fuses, especially if the wiring is not also over rated. (the voltage is not relevant, its the current that blows the fuse)
 
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