Battery maintenance — how much solar is enough?

[WhereStream]

I want to use a small solar panel to maintain the charge on the two lead-acid batteries that power up our 2017 19-footer.

How much solar would I need, just to keep the batteries charged (with the parasitic drains and occasional use of lights)?

My International came with a Zamp plug, down near the batteries (and a set of plugs on the roof). I assume I could plug a small solar panel into the Zamp connection and ... that's all I'd need to do, right?

As you can tell, I'm not of the solar cognoscenti.

[JeffKim]

I'm not part of the card-carrying cognoscenti (they are very shadowy), but if you're trying top off with various loads a solar panel would be a good addition. There are many in the 200W range. We like our Renogy 220W. It's sturdy and doesn't flop around like some. You need to either buy one with a solar controller (Renogy offers one) or install a solar controller. MPPT controllers are superior to a cheaper PVM. Also, if you use the Zamp plug-in you will need a MP4 to SAE adapter with a polarity reversal adapter. Something like this.

Back of the envelope, I don't know the size of your batteries but with 2x100Ah or 2400W and you discharge 1/2 way with lead-acid that's 1200W of charging. So, with a 200W panel under ideal conditions it would take around 12 hours to charge. But even in the strong Florida sun, I wouldn't count on more than 50% of this or 24 hrs. Therefore, you can't count on it recharging your batteries.

But with normal usage, you don't have a 12V DC refrigerator so you could get a battery's worth of charging which I'd think would work pretty well to keep up with your loads with a ceiling of 1200W or so.

[Rolind]

We store our trailer under cover and use a Renogy 100w panel with a Renogy wanderer charge controller. Inexpensive and easy to use. This is more than enough to keep up with parasitic draws and will charge the battery to a higher SOC slowly. Because of the orientation of the storage unit, we only get about 5-6 hrs of sun exposure on the panel per day but is is more than enough to keep the batteries topped off.
This works well for us and we almost never bring the extra panel along when we camp off grid. It also doesn’t seem like a high risk for theft, it looks kinda old after sitting outside for a couple of years.
If you think you would want to use the solar for off grid adventures, I think a 200w solar suitcase would be a better choice.
Remember that zamp outlets have reverse polarity compared to most other solar product.

[Forester2]

I use a Renogy 200 watt suitcase (that comes with a contoller) in the Zamp plug on tongue. NOTE: Check polarity on your plug. Airstreams seem to be the reverse of everyone else. You'll get an error message on your contoller. I just reversed the wires on the triler side of the plug. Battery chaeging of course dwpends on your usage: lights, water pump , fridge etc...

[gypsydad]

I have been using my 80W GoPower solar suitecase to charge my 2, 6V Trojan2 batteries for several years, untill I installed my 2 new LiTime 12V 200AH batteries few months ago. I could go only a 2-3 days without charging when boondocking without using the GoPower. I could usually get a nice top off using the sun for 4-6 hours without any issues. Real game changer was moving to the Li batteries; think about you only get "maybe" 40-50% use of your lead acid batteries before your down to <12V. I recently ran my Li batteries 5 days without any charge and still had 56% usage available and 12.7V. I would suggest looking at the trade off in cost of portable solar and Li batteries...m 2cents.

[WhereStream]

Originally Posted by gypsydad

I have been using my 80W GoPower solar suitecase to charge my 2, 6V Trojan2 batteries for several years, untill I installed my 2 new LiTime 12V 200AH batteries few months ago. I could go only a 2-3 days without charging when boondocking without using the GoPower. I could usually get a nice top off using the sun for 4-6 hours without any issues. Real game changer was moving to the Li batteries; think about you only get "maybe" 40-50% use of your lead acid batteries before your down to <12V. I recently ran my Li batteries 5 days without any charge and still had 56% usage available and 12.7V. I would suggest looking at the trade off in cost of portable solar and Li batteries...m 2cents.

Thanks. I'm considering going to lithium batteries when the lead-acid boxes wear out.

For now, though, they are doing fine, and I'm hoping to find an inexpensive solar panel I can leave out to keep them charged while the rig is parked next to the house.

Currently, I'm keeping the rig plugged in, using the converter to keep the batteries up. But, two things:

-- One, my wife wants me to get rid of the extension cord running off the front porch and around to the side of the house.

-- Two, I worry that I'm putting a lot of use on the converter, which I've already had to replace (and that's not a cheap or simple swap).

With that in mind, it sounds like an 80-watt unit would do the job. Could I get by with less?

[WhereStream]

Originally Posted by Forester2

I use a Renogy 200 watt suitcase (that comes with a contoller) in the Zamp plug on tongue. NOTE: Check polarity on your plug. Airstreams seem to be the reverse of everyone else. You'll get an error message on your contoller. I just reversed the wires on the triler side of the plug. Battery chaeging of course dwpends on your usage: lights, water pump , fridge etc...

Thanks.

Mine has the Zamp outlet, so reversed, from what I've been told.

I assume I could simply cut the wires (either on the solar panel or on the trailer) and reconnect them to correct the polarity.

I may want a 200-watt unit one day, but we usually stay at campgrounds with power, so no urgency.

For now, I want to attach a small (how small?) unit to keep the batteries charged while the trailer is not in use. Trailer is outside, so the panel would get a lot of sun.

[WhereStream]

Originally Posted by Rolind

We store our trailer under cover and use a Renogy 100w panel with a Renogy wanderer charge controller. Inexpensive and easy to use. This is more than enough to keep up with parasitic draws and will charge the battery to a higher SOC slowly. Because of the orientation of the storage unit, we only get about 5-6 hrs of sun exposure on the panel per day but is is more than enough to keep the batteries topped off.
This works well for us and we almost never bring the extra panel along when we camp off grid. It also doesn’t seem like a high risk for theft, it looks kinda old after sitting outside for a couple of years.
If you think you would want to use the solar for off grid adventures, I think a 200w solar suitcase would be a better choice.
Remember that zamp outlets have reverse polarity compared to most other solar product.

Thanks, Rolind.

This is very helpful.

[WhereStream]

Originally Posted by JeffKim

I'm not part of the card-carrying cognoscenti (they are very shadowy), but if you're trying top off with various loads a solar panel would be a good addition. There are many in the 200W range. We like our Renogy 220W. It's sturdy and doesn't flop around like some. You need to either buy one with a solar controller (Renogy offers one) or install a solar controller. MPPT controllers are superior to a cheaper PVM. Also, if you use the Zamp plug-in you will need a MP4 to SAE adapter with a polarity reversal adapter. Something like this.

Back of the envelope, I don't know the size of your batteries but with 2x100Ah or 2400W and you discharge 1/2 way with lead-acid that's 1200W of charging. So, with a 200W panel under ideal conditions it would take around 12 hours to charge. But even in the strong Florida sun, I wouldn't count on more than 50% of this or 24 hrs. Therefore, you can't count on it recharging your batteries.

But with normal usage, you don't have a 12V DC refrigerator so you could get a battery's worth of charging which I'd think would work pretty well to keep up with your loads with a ceiling of 1200W or so.

Thanks. Good info.

[GOUSC]

Originally Posted by WhereStream

Thanks.

Mine has the Zamp outlet, so reversed, from what I've been told.

I assume I could simply cut the wires (either on the solar panel or on the trailer) and reconnect them to correct the polarity.

I may want a 200-watt unit one day, but we usually stay at campgrounds with power, so no urgency.

For now, I want to attach a small (how small?) unit to keep the batteries charged while the trailer is not in use. Trailer is outside, so the panel would get a lot of sun.

No need to cut the wires. There are adaptors out there that you can simply plug into to reverse the connection. $5 for these

[WhereStream]

Originally Posted by GOUSC

No need to cut the wires. There are adaptors out there that you can simply plug into to reverse the connection. $5 for these

Nice to know. Thanks!

Why in the world did Zamp go in reverse?

[AlbertF]

Originally Posted by WhereStream

I want to use a small solar panel to maintain the charge on the two lead-acid batteries that power up our 2017 19-footer.

How much solar would I need, just to keep the batteries charged (with the parasitic drains and occasional use of lights)?

My International came with a Zamp plug, down near the batteries (and a set of plugs on the roof). I assume I could plug a small solar panel into the Zamp connection and ... that's all I'd need to do, right?

As you can tell, I'm not of the solar cognoscenti.

If you use a 5 watt panel for this purpose you might be able to plug it in directly to the port without using a controller if it’s designed for trickle charging.

That would give you one or two amp hours per day.

[Redbarron55]

I am currently conducting an experiment with my solar / LiFePO4 battery system I just completed.
Quick background
Recently bought a 1985 25' Sovereign and removed the front battery and added 3 100 AH Chins lithium batteries under the streetside twin bed. Also installed a ProMarine 2000 watt inverter and 4 Eco-Worthy 100 watt solar panels. The two way propane refrigerator was replaced with a Danfoss electric unit.
So 300 AH of battery and 400 Watts (possibly) of solar panels and the major continuous load is the refrigerator.
As it happens the first day the sun was shining and the batteries were charged back to 100%. Since that time we have had pretty much continuous overcast and rain, giving me a chance to see just how long the batteries will run the fridge.
It seems that the refrigerator uses about 15 - 18 % of that 300 AH a over the solar "night" and perhaps the solar holds that even during the day.
The system has run 4 days and was at 48% this morning as the sun started to charge. Since that time this morning there has been enough sun to hold it's own and still at 48% three hours later.
The batteries have provided about 168 Ah so far this charge cycle and the Victron Smart Shunt says that there is almost 2 days left in the batteries. (depending on if you look at the APP when the fridge compressor is running or not as it calculates based on the current load)
The Refrigerator seems to draw about ~ 40 watts and the duty cycle is about 50% for an average of perhaps 20 Watts and maybe 500 watt hours for 4 days.
My plan is to operate with the solar until the batteries are depleted to some point and then turn on the PD4060 charger to bring them back up if the "sun don't shine". If the sun shines to see just how long it takes here in north Florida to get fully charged or where the equilibrium point might be.

[JeffKim]

Originally Posted by WhereStream

Nice to know. Thanks!

Why in the world did Zamp go in reverse?

With standard SAE connectors the positive is the exposed metal connection. I think Zamp says it's safer to not have this exposed and possibly short to a ground. Zamp makes it sound proprietary but all it is is a SAE with the connections reversed.

I think it's best to leave it hooked up the way it comes and use an adapter. The port is directly wired to the battery with a 15A fuse and swapping wires puts the fuse on the negative which is non-standard and also makes wiring more confusing.

I'll also add to the shopping list a 10AWG extension cable. You'll need it to position the panel. Ours is a 20' from Amazon (where else?). You can go with a lesser gauge, but then the voltage drop becomes a factor.

[WhereStream]

Originally Posted by AlbertF

If you use a 5 watt panel for this purpose you might be able to plug it in directly to the port without using a controller if it’s designed for trickle charging.

That would give you one or two amp hours per day.

Thanks. That might be all I need.

[WhereStream]

Originally Posted by JeffKim

With standard SAE connectors the positive is the exposed metal connection. I think Zamp says it's safer to not have this exposed and possibly short to a ground. Zamp makes it sound proprietary but all it is is a SAE with the connections reversed.

I think it's best to leave it hooked up the way it comes and use an adapter. The port is directly wired to the battery with a 15A fuse and swapping wires puts the fuse on the negative which is non-standard and also makes wiring more confusing.

I'll also add to the shopping list a 10AWG extension cable. You'll need it to position the panel. Ours is a 20' from Amazon (where else?). You can go with a lesser gauge, but then the voltage drop becomes a factor.

Thanks.

I see the adapter is not hard to find and not costly, so I'll skip the wire snip.

[JeffKim]

Originally Posted by WhereStream

Thanks. That might be all I need.

I don't want to rain on the parade, but I don't see how 5W gets you very far. One LED light consumes 3W or more and a 5W panel isn't 100% efficient as well.

[Rolind]

Originally Posted by WhereStream

Thanks. That might be all I need.

I tried this with a small dashboard type 12 watt panel and honestly didn’t see and appreciable charging.

[daleyocum]

I all you want to do is maintain the battery and have something small, a little 10-15w panel will do that well. I’d still get one with a controller. This is one example.

[Castaway]

Originally Posted by AlbertF

If you use a 5 watt panel for this purpose you might be able to plug it in directly to the port without using a controller if it’s designed for trickle charging.

That would give you one or two amp hours per day.

This what I do with 2 Lead Acid for 4 years and now with LIon for 2 and it works fine but I get 7-10 hrs sunlight.