Charging 24v battery bank with 12vg

[Chris1]

Absolutely it can be done, but why would you? It can be done if you charge each 12-volt separately. Good luck with that.

But why if you do not have to. Wire you panels in series and set charger up for 24 volts. Personally I would not bother with putting up 2 small 50 watt panels on a boat. Shade will always be an issue, and with no fixed tilt or orientation to optimize solar harvest, you can fart more usable energy then the panels will produce in poor conditions. Wind Turds work better for boats.

If it were me I would buy a good High Voltage Grid Tied of 250 to 300 watts which cost less then your 2 x 12 volt battery panels, use the savings to buy a good MPPT charge controller configured for 24 volts, and forget about solar panel dead weight in the boat to slow you down with no meaningful power generated. At 250 to 300 watts into a 24 volt battery will require a small 15 amp controller. Morning Star makes a SunSaver MPPT 15 amp charge controller which should be perfect.

Here is some math to crunch. If you used PWM controller with your 2 x 50 wat panels on its best day with the panels facing directly into the sun at high noon on June 21 might briefly output 60 watts or roughly 2.4 amps of charge current or 60 watts. The farts from a can of beer will generate more energy and not near as big and heavy. Want to use those 2 x 100 watt panels for shore power. Well they will give you up to 4.8 amps of charge current or 12 watts.

Use a single GT panel of say 250 watts, a MPPT charge controller and you get 10.4 charge amps or roughly the full 250 watts. Who on earth would have thought you could get 250 watts from a 250 watt panel? You can if you toss those antiquated PWM Controllers over board and send them to Davy Jones Locker where they belong. Anyway you would have to be a serious alcoholic to generate more beer fart power than aa 250 watt panel with an MPPT controller. Not to mention less expensive than PWM. To get 250 watts from a PWM controller will require 375 watts. With your idea of using 100 watts from the boat, plus another 200 watts from shore only gives 8.3 amps of charge current or roughly 200 watts from 300 watts of panels.

Ha. Okay thanks Sunking. It's going to take me a bit to decipher what you've written. Two quick thoughts: I don't have shore power available at the dock, and wind power is as good as non existent in the cove where the dock is. Good thoughts though for sure. Now that I think about it though the wind generator would be doing some work when the boat's out sailing, hmmm... got to mull the trade-offs over. The MPPT controllers look like lovely things alright. A little pricey but okay. I don't have a good place to put it where I can guarantee no occasional salt water splash. Remember this is a SMALL sailboat. That's why I was drawn to that waterproof PWM controller. But I'm a boat builder, I can make places for things that need to stay dry if I have to. From the cooling fins I see on those MPPT controllers I'm guessing they need to breath a bit.

That SunSaver unit looks good. I guess I shouldn't sweat the price but jeez, it starts to add up. Anyway you've given me a lot to think about. I really appreciate the help.

If you are still willing, can you tell me why some battery mfgs. list a minimum solar panel size with which to charge their AGM batteries? I'm thinking of Vmax in particular. While Renogy wrote to tell me just today that it doesn't matter, it just takes longer with a little solar panel. What to believe?

[Sunking]

How many watts does a typical beer fart contain? More than a popcorn fart, but less than a pickled egg fart is my guess.

That is how I smell it.

[littleharbor]

Absolutely it can be done, but why would you? It can be done if you charge each 12-volt separately. Good luck with that.

But why if you do not have to. Wire you panels in series and set charger up for 24 volts. Personally I would not bother with putting up 2 small 50 watt panels on a boat. Shade will always be an issue, and with no fixed tilt or orientation to optimize solar harvest, you can fart more usable energy then the panels will produce in poor conditions. Wind Turds work better for boats.

If it were me I would buy a good High Voltage Grid Tied of 250 to 300 watts which cost less then your 2 x 12 volt battery panels, use the savings to buy a good MPPT charge controller configured for 24 volts, and forget about solar panel dead weight in the boat to slow you down with no meaningful power generated. At 250 to 300 watts into a 24 volt battery will require a small 15 amp controller. Morning Star makes a SunSaver MPPT 15 amp charge controller which should be perfect.

Here is some math to crunch. If you used PWM controller with your 2 x 50 wat panels on its best day with the panels facing directly into the sun at high noon on June 21 might briefly output 60 watts or roughly 2.4 amps of charge current or 60 watts. The farts from a can of beer will generate more energy and not near as big and heavy. Want to use those 2 x 100 watt panels for shore power. Well they will give you up to 4.8 amps of charge current or 12 watts.

Use a single GT panel of say 250 watts, a MPPT charge controller and you get 10.4 charge amps or roughly the full 250 watts. Who on earth would have thought you could get 250 watts from a 250 watt panel? You can if you toss those antiquated PWM Controllers over board and send them to Davy Jones Locker where they belong. Anyway you would have to be a serious alcoholic to generate more beer fart power than aa 250 watt panel with an MPPT controller. Not to mention less expensive than PWM. To get 250 watts from a PWM controller will require 375 watts. With your idea of using 100 watts from the boat, plus another 200 watts from shore only gives 8.3 amps of charge current or roughly 200 watts from 300 watts of panels.

How many watts does a typical beer fart contain? More than a popcorn fart, but less than a pickled egg fart is my guess.

[Sunking]

This may be a stupid question but here goes - Can a 24v battery bank (two 12v, 100Ah AGM batteries) be charged with a 12v solar controller?

Absolutely it can be done, but why would you? It can be done if you charge each 12-volt separately. Good luck with that.

But why if you do not have to. Wire you panels in series and set charger up for 24 volts. Personally I would not bother with putting up 2 small 50 watt panels on a boat. Shade will always be an issue, and with no fixed tilt or orientation to optimize solar harvest, you can fart more usable energy then the panels will produce in poor conditions. Wind Turds work better for boats.

If it were me I would buy a good High Voltage Grid Tied of 250 to 300 watts which cost less then your 2 x 12 volt battery panels, use the savings to buy a good MPPT charge controller configured for 24 volts, and forget about solar panel dead weight in the boat to slow you down with no meaningful power generated. At 250 to 300 watts into a 24 volt battery will require a small 15 amp controller. Morning Star makes a SunSaver MPPT 15 amp charge controller which should be perfect.

Here is some math to crunch. If you used PWM controller with your 2 x 50 wat panels on its best day with the panels facing directly into the sun at high noon on June 21 might briefly output 60 watts or roughly 2.4 amps of charge current or 60 watts. The farts from a can of beer will generate more energy and not near as big and heavy. Want to use those 2 x 100 watt panels for shore power. Well they will give you up to 4.8 amps of charge current or 12 watts.

Use a single GT panel of say 250 watts, a MPPT charge controller and you get 10.4 charge amps or roughly the full 250 watts. Who on earth would have thought you could get 250 watts from a 250 watt panel? You can if you toss those antiquated PWM Controllers over board and send them to Davy Jones Locker where they belong. Anyway you would have to be a serious alcoholic to generate more beer fart power than aa 250 watt panel with an MPPT controller. Not to mention less expensive than PWM. To get 250 watts from a PWM controller will require 375 watts. With your idea of using 100 watts from the boat, plus another 200 watts from shore only gives 8.3 amps of charge current or roughly 200 watts from 300 watts of panels.

[Chris1]

This may be a stupid question but here goes - Can a 24v battery bank (two 12v, 100Ah AGM batteries) be charged with a 12v solar controller?

Here are the details: This is for a small sailboat that will have a 24v electric outboard installed. There is room on the boat to install two 50 watt, 12v panels - I'm thinking these would be Monocrystalline panels with bypass diodes, VOC is 22.7.

Because there will be some shading from the sailboat's rigging I'd like to wire the panel's in parallel to minimize shading loss.

I'd like to use the Renogy PWM 20a, 12v controller as it is waterproof and fits the available space well.

If this won't work I guess it would be no big deal to get another 12v controller and set up two charging systems. Is that right?

In addition my plan is to set up two 100w panels on the boat's dock. These will plug in to the boat's system when it is tied up there (most days, all summer).

Is there a better way?

Thanks in advance for any thoughts. You guys are a wealth of information.