Attaching extra solar panel to batt for a bit of extra humph

[simonpickard]

Hello all,

I've got a spare 100watt panel that I was thinking of just wiring directly to the batt terminals when the charge is a little low and I want a bit of extra juice in the tank. I have 300watts on board that is wired through a controller but is there any issue in just wiring this 'temp' panel straight to the batteries if I do it sensibly and don't let it overcharge the battery?

Any ideas on this would be most welcomed.

Regards,
Simon

[onestepcsy37]

I know i'm going to get 'dissed' on the forum for saying this, but I used to cruise around without a solar controller for years. I had a 130 watt kyocera and a 450 amp hour battery bank. My daily draw was about 80 amps a day. At full blast, the solar panel might put out 50 amps a day, so there was no chance that the bank could be overcharged as long as my 'out' was much greater than my 'in'. Over the years I could detect no indications of battery damage because of the 'uncontrolled' charging.

So what i'm saying is that if you keep an eye on everything, and in your situation you probably will, there should be no problem.

Having said this, I did eventually - after maybe five years - install a PWM controller.

Now, although I find it hard to believe, there are some members here who really do know more than me, especially about solar. They might be able to figure out the other problem with your installation. That is, when your 'uncontrolled' solar panel is charging, how does this affect the 'controlled' panels? Would it make them think the battery is fully charged (because the uncontrolled panel is charging at a higher voltage) and so reduce their charging rate or even shut them down? I don't know.

[colemj]

We were struck by lightning and our solar controller was one of the many things destroyed. For 3 weeks, I simply directly connected our 480W of solar panels directly to the 600Ahr house bank (which was down to 400Ahr after removing the 2 boiled batteries from the strike).

Worked perfectly, and I never even had to disconnect them since our usage ate up all they could deliver.

So you will be OK doing this as long as you never forget and leave it on when the batteries are full. If FLA, then even that isn't a big issue, but if gel or agm, you could ruin them.

However, why not just mount it permanently and run it through your existing regulator? Seems odd to have a panel that large simply laying about and being brought into use occasionally.

Mark

[Nicholson58]

Originally Posted by colemj

We were struck by lightning and our solar controller was one of the many things destroyed. For 3 weeks, I simply directly connected our 480W of solar panels directly to the 600Ahr house bank (which was down to 400Ahr after removing the 2 boiled batteries from the strike).

Worked perfectly, and I never even had to disconnect them since our usage ate up all they could deliver.

So you will be OK doing this as long as you never forget and leave it on when the batteries are full. If FLA, then even that isn't a big issue, but if gel or agm, you could ruin them.

However, why not just mount it permanently and run it through your existing regulator? Seems odd to have a panel that large simply laying about and being brought into use occasionally.

Mark

all true BUT the open circuit voltage of various panels need to be about the same. If all of the panels ope circuit are a bit above the nominal charge voltage then you can wire direct. What you loose is the benefit of a multistage charger and add the possibility of over-charge.

My boat is 24 VDC with 54 VDC open circuit panels so we have MPPT. I also am adding a flex panel or two that can be stored under a mattress. We will use it for lap-tops and as emergency back-up should our stuff get fried.

On the lightning thing, We've been struck twice in three years on the Great Lakes. The observation I have made is that items with total air gap shut-off switches on both positive & negative leads near the device have survived. We are now adding this capability to everything. Its black art, guess & luck, but it can't hurt.

[onestepcsy37]

Originally Posted by colemj

We were struck by lightning and our solar controller was one of the many things destroyed.

Interesting. We were also hit by lightning, and among the things that were NOT damaged were all those things directly connected to the battery instead of through the breaker panel. Solar panel/controller, autopilot, and fridge were unharmed.

Nicholson58 wrote -
"On the lightning thing, We've been struck twice in three years on the Great Lakes. The observation I have made is that items with total air gap shut-off switches on both positive & negative leads near the device have survived. We are now adding this capability to everything. Its black art, guess & luck, but it can't hurt."

Interesting. All of our electronics that went through the breaker panel were fried, except one. I checked each device for blown fuses but they were all ok. Except for the Furuno Navtex. It had a fuse on BOTH the positive and negative wires. The negative wire fuse was blown. I replaced it and it came right back up. I don't know why but I am now fusing electronics on both positive and negative wires. As he wrote, " Its black art, guess & luck, but it can't hurt."

[colemj]

Yes, I did assume a 100W panel was a nominal "12V" one.

Mark

[Ex-Calif]

Originally Posted by simonpickard

Hello all,

I've got a spare 100watt panel that I was thinking of just wiring directly to the batt terminals when the charge is a little low and I want a bit of extra juice in the tank. I have 300watts on board that is wired through a controller but is there any issue in just wiring this 'temp' panel straight to the batteries if I do it sensibly and don't let it overcharge the battery?

Any ideas on this would be most welcomed.

Regards,
Simon

If you have an appropriately fused Cig plug outlet I would wire a plug on it and make it easy-peasy...

Saves opening up the battery compartment when you need the extra ooomph...

[MarkJ]

I had 240 watts of solar directly connected to the battery and it was fine for the two years till I could afford a controller.

I think you will be fine. Just keep and eye on it.

Btw i have 310 watts solar going through a controller and a wind gererator going through its own controller and either the talk to each others electrons like a line of ants or the controllers just factor in everything in total.

[Nicholson58]

Originally Posted by onestepcsy37

Interesting. We were also hit by lightning, and among the things that were NOT damaged were all those things directly connected to the battery instead of through the breaker panel. Solar panel/controller, autopilot, and fridge were unharmed.

Nicholson58 wrote -
"On the lightning thing, We've been struck twice in three years on the Great Lakes. The observation I have made is that items with total air gap shut-off switches on both positive & negative leads near the device have survived. We are now adding this capability to everything. Its black art, guess & luck, but it can't hurt."

Interesting. All of our electronics that went through the breaker panel were fried, except one. I checked each device for blown fuses but they were all ok. Except for the Furuno Navtex. It had a fuse on BOTH the positive and negative wires. The negative wire fuse was blown. I replaced it and it came right back up. I don't know why but I am now fusing electronics on both positive and negative wires. As he wrote, " Its black art, guess & luck, but it can't hurt."

Sorry for the confusion, I should have been more specific. All of our fried items were fed from the breaker panel and many had local Buss fuses as well. The items not damaged also had a local mechanical double pole toggle switch that broke both plus & minus wires and these switches were within 12 inches of the device. Notable, is that most electronic devices have software switches and so are nominally hot always. Leaving only a short lead from the dry contact may eliminate EM induced spikes in either line. That's my best guess at the black art of lightning voodoo.

Our last strike was a direct hit observed by a marina neighbor. It vaporized our windex, leaving melted SS & aluminum on the deck. Lost were all main mast LED lights, deck lights, nav lights, some mizzen mast lights, forward cabin LEDs, Std Hor VHS radio, 1.5 kw alternator on the generator, Generator charge controller, AIS, depth, wind instruments, 14 Buss fuses, stereo and the autopilot. The brains were scrambled on the 2.5 KW Xantrex but recovered on a re-boot. All forward cabin lighting wire was fused.

The notable survivor was the SSB & SIMRAD chart plotter, Radar, and depth scanner as well as the on-deck repeater. These survivors had the local disconnects. One other survivor was the lightning arrestor on the main mast. HA HA. The bolt split and took out one of my neighbors too.

[Cavalier]

Originally Posted by MarkJ

...either they talk to each others electrons like a line of ants...

I love the idea of such a physical mechanism

[simonpickard]

We have nowhere else to mount it which is why it's just stored under the rear bunk (it's Flexi).

What did you mean about wore a cig plug with fuse on?

I was going to add a simple push connector so I can add the panel to the bank easy but why would I need a fuse?



Please visit my blog:
www.sailing-interlude.com

[Cadence]

Originally Posted by simonpickard

Hello all,

I've got a spare 100watt panel that I was thinking of just wiring directly to the batt terminals when the charge is a little low and I want a bit of extra juice in the tank. I have 300watts on board that is wired through a controller but is there any issue in just wiring this 'temp' panel straight to the batteries if I do it sensibly and don't let it overcharge the battery?

Any ideas on this would be most welcomed.

Regards,
Simon

Maybe someone can straighten me out. Knowing nothing about the controllers I would suspect the single panel, unregulated, may shut down feed from the main panels since a false voltage may be obvious at the controllers output?

[simonpickard]

Yeah that's what was worrying me. I want to mix both I guess.

The only other thing I can think of is to tee in the main panels cables just before they hit the controller. Then attach the spare panel to a connector there so they are fed into the controller also.

Would that cause any issues? All of the panels are 12v and of similar voltages.

Regards,
Simon



Please visit my blog:
www.sailing-interlude.com

[donradcliffe]

If you have a cigarette lighter plug which is run off a breaker in the main panel, you don't need to worry about a fuse--just plug the solar panel in when you want to. Don't over think about the controller on the solar panel--it will do its job and throttle down the output from the other panels when the battery gets full. The only thing you have to think about is not plugging in the extra panel when the batteries are full--like when you are plugged into the dock, or have motored for 12 hours.

[Ex-Calif]

Originally Posted by simonpickard

We have nowhere else to mount it which is why it's just stored under the rear bunk (it's Flexi).

What did you mean about wore a cig plug with fuse on?

I was going to add a simple push connector so I can add the panel to the bank easy but why would I need a fuse?



Please visit my blog:
Sailing-Interlude | Sailing the Med… and beyond

What Don says below - I figured a cig plug outlet would be easy - your idea to wire a plug into the solar harness is a good idea as well. Then the extra oomph is regulated if that's what you mean.

Originally Posted by Cadence

Maybe someone can straighten me out. Knowing nothing about the controllers I would suspect the single panel, unregulated, may shut down feed from the main panels since a false voltage may be obvious at the controllers output?

Imagine a river flowing along - huge volume. You squirt a garden hose in. Maybe a little turbulence at the point of entry but the river doesn't speed up. Not the best analogy but I'm only one coffee in this morning.

Mathematically this might explain. A discharged bank when charging has "high" resistance. V=I/R so when you plug an unregulated 18V panel into a discharged system the resistance of the system (with say a 12.6V charge) drags down the voltage. i.e. when you stick that panel on you won't see 18V on the DC bus.

As the batteries reach full charge and resistance goes down the voltage on the panel will go up and for a 100w panel you may be still shoving 6-8 amps in. That's why you don't want large unregulated panels on a charged system.

Originally Posted by donradcliffe

If you have a cigarette lighter plug which is run off a breaker in the main panel, you don't need to worry about a fuse--just plug the solar panel in when you want to. Don't over think about the controller on the solar panel--it will do its job and throttle down the output from the other panels when the battery gets full. The only thing you have to think about is not plugging in the extra panel when the batteries are full--like when you are plugged into the dock, or have motored for 12 hours.

Yup the fuse comment was just that it is preferable to clipping the panel directly to the battery.

So...

- Wire a plug into the current solar bank and regulate the extra panel
- Plug it into an already fused circuit like a cig plug