12v vs 24v

OldJimbo

New Member
I have 4 of the NewPowa 100 watt 5.83 amp “mis-aligned” panels. I’m wanting to connect them in parallel and use MC4 connectors to go through the roof of the van and into an mppt controller, then into 2 12v x 100 ah batteries (either AmpTime or MJBSAN). Now I’m worried about 1. Will the 10g Renogy wires take the amps and 2. Will a 30 amp controller be sufficient?
I’ve been searching and reading lots of threads and Wills’ book, but just seem to get lost in the weeds. Money is always a consideration since I’m old & feeble. Can I get a “go ahead” on the 12v system? And finally, Will suggested buying a controller with protection agains 32 degree F charging. Are there any besides Victron?
Please excuse the length of this post.
 

Rednecktek

Solar Enthusiast
If you're using a MPPT controller you can string those panels together into some series or series/parallel for more even power generation. You'll need to look at the VoC of your panels and the max input voltage of your controller to figure out the best way to connect the panels. Just off hand I'm suspecting that with a 30 amp MPPT you'll be looking at doing a 2s/2p setup which means that each set of panels would only pump through less than 12a which would be 14AWG (15a max) wire, or 12AWG (20a max) if you like to overjudge it to be safe. 10AWG is way overkill.

With 400w of panel at 12v that's roughly 40a so I'd recommend aiming for at least a 40a to be safe, 50 or 60 if you can get a good deal. You'll want probably 6AWG for the controller to batteries and between 2AWG and 1/0AWG for batteries to inverter depending on size of inverter.

Do you need 12v power for the rest of the van stuff? If so, keep it at 12v and just use a 1500w or smaller inverter.

If you don't need 12v for the van, go for 24v and you can get a nice 3000w inverter on there if you really felt like it.

The biggest advantage to doing a higher voltage system is that you need half the wire size for double the voltage and copper is expensive and hard to bend. The down side is that if you need lower voltages for anything else you're into buck transformers and step down's.

Most decent MPPT controllers will have a temperature probe port you can connect to a probe in your battery compartment, it'll let the controller adjust the charge rate for temperature. If you go with Lithium batteries they should have low-voltage cut off to keep them from charging below freezing. Other than that I don't know as I'm an AGM fan. :)

So once you have an idea of what parts you want to do, throw it up here and let the folk here figure out what you're missing, because we ALL miss something our first go 'round. Also post your budget if you have one so we can make recommendations to fit it.
 

OldJimbo

New Member
If you're using a MPPT controller you can string those panels together into some series or series/parallel for more even power generation. You'll need to look at the VoC of your panels and the max input voltage of your controller to figure out the best way to connect the panels. Just off hand I'm suspecting that with a 30 amp MPPT you'll be looking at doing a 2s/2p setup which means that each set of panels would only pump through less than 12a which would be 14AWG (15a max) wire, or 12AWG (20a max) if you like to overjudge it to be safe. 10AWG is way overkill.

With 400w of panel at 12v that's roughly 40a so I'd recommend aiming for at least a 40a to be safe, 50 or 60 if you can get a good deal. You'll want probably 6AWG for the controller to batteries and between 2AWG and 1/0AWG for batteries to inverter depending on size of inverter.

Do you need 12v power for the rest of the van stuff? If so, keep it at 12v and just use a 1500w or smaller inverter.

If you don't need 12v for the van, go for 24v and you can get a nice 3000w inverter on there if you really felt like it.

The biggest advantage to doing a higher voltage system is that you need half the wire size for double the voltage and copper is expensive and hard to bend. The down side is that if you need lower voltages for anything else you're into buck transformers and step down's.

Most decent MPPT controllers will have a temperature probe port you can connect to a probe in your battery compartment, it'll let the controller adjust the charge rate for temperature. If you go with Lithium batteries they should have low-voltage cut off to keep them from charging below freezing. Other than that I don't know as I'm an AGM fan. :)

So once you have an idea of what parts you want to do, throw it up here and let the folk here figure out what you're missing, because we ALL miss something our first go 'round. Also post your budget if you have one so we can make recommendations to fit it.
 

OldJimbo

New Member
I’ve thought about AGM because of the short term money savings. Since I turn 75 this winter, I don’t really need a 5 or 10 year battery - plus I have glaucoma, and won’t be driving the van for that much longer. The downside to AGM seems to be the price - they’re about 80% of a lifepo4 here in Arkansas, so why not step up to the newest technology?
 

Rednecktek

Solar Enthusiast
80% of Lith? Where do you shop, I want some! :) Everywhere I look the Lithium's are either Shady-Chinese-Brand-From-Aliexpress or about 4 times the cost of their AGM counterparts. Even factoring in for the reduced DoD of AGM, it still comes out to about half or less for the same usable amp hours. Also, AGM's are a 5-10yr battery if you don't abuse them.

If you can afford it and don't mind doing some programming on your charge controllers and you're not hanging out in the arctic there's no reason NOT to go for the LiFePo4's or the like. Less weight, higher usable amp hours per cubic inch, bragging rights. What more can you ask for? :)
 

OldJimbo

New Member
Don’t really want to do any service on batteries, but I will check out Wal-Mart. Sam’s is pretty high, but they’re AGM. Trolling motor, golf cart and now Dual Purpose. What’s the difference?
Amazon has 12v 100 ah LiFePO4 batts from MJBSAN for $335 each, including shipping. That’s tough to ignore, even if they’re Chinese. Wish Will had a tear down video on them. We get under 30 degrees F a couple of times a year here and I want to sleep in the house whenever near home, so I’m still worried about low temp charging. Most makers of lifepo4 batteries and solar chargers don’t talk about it, but I’m still looking for a good affordable solution.
 

OldJimbo

New Member
My budget is Cheap and CHEAPER, but sometimes my better judgment lifts me way up the price ladder. Don’t want to prematurely wake up dead.
 

12VoltInstalls

Solar Addict
Trolling motor, golf cart and now Dual Purpose.
A trolling motor battery should be a commodity deep cycle battery. Often they’re closer if not not the same as a dual purpose.

A golf cart battery is most generally a heavy thick-plated deep cycle 6V 3-cell battery

A dual purpose is supposed to be a lighter-plate deep cycle, giving more surface area than a deep cycle for starting battery purposes but still have some of the vibration resistance and bulk of a marine deep cycle battery.

Some say the walmartha deep cycles are not real deep cycle batteries but they’re as good (and/or perhaps better) than many commodity-level deep cycle battery imho
 

Rednecktek

Solar Enthusiast
Some say the walmartha deep cycles are not real deep cycle batteries but they’re as good (and/or perhaps better) than many commodity-level deep cycle battery imho

AND cheap, AND readily accessible I use them for my camp and I'll be using them for Phase-1 of my neighbor's place rebuild.
 

12VoltInstalls

Solar Addict
AND cheap,
Yup. I intended 3 or maybe 4 Grp31s but cost per labeled amp-hour for the 27s was surprisingly way less AND they weigh less!
I wound up buying four 27s instead of three 31s; later added a fifth one. Hard to beat $67 each + tax. Iirc the 31s were $105 so basically the same money, a bit more Ah
 

Rednecktek

Solar Enthusiast
Yep, those are cheap. I use the 29's myself at $88 plus core, so just shy of $110 out the door just for the extra Ah's with my limited shelf space. I'll be adding 2 to my system when I convert it all to a 24v setup on an AIO this fall. Next phase is to replace them all with AGM 120Ah versions, but I gotta get the rest of the infrastructure in place first.
 

12VoltInstalls

Solar Addict
AGM 120Ah
I personally don’t see AGM as a good expense unless maybe an offroad trail vehicle.
If I change batteries I’d go for an upgrade instead and go lifepo or whatever new thing that’s supposedly coming next year or two that supposedly leaves lifepo in the dust and is “safer” and is said to cost less.
 

Rednecktek

Solar Enthusiast
I only want to go AGM because of the FLA maintenance that I'm physically not capable of doing. Checking the water levels every month? I'm on a ship in the Persian Gulf or bouncing around Asia and Guam for 6+ months at a time and that would be a RREEAALLYY long swim to check those. Having the sealed AGM is just removing the maintenance.
 

OldJimbo

New Member
I’m still locked in the struggle over lead acid vs lifepo4. Can’t do flooded because of the maintenance…
So, it’s a cheap lithium vs a cheap lead battery, and lithium has the upper hand. The Connect has very limited weight capacity and I still want to take most of my Makita battery powered tools and about 50# of other tools - then a 20# propane tank, fridge and whatever - including guns and ammo.
Need to make a decision this week on 12 vs 24 volt. Leaning towards 24v because of the four matched 12 v 100 watt panels. The Vmp is 17.0 volts - Imp is 5.89 amps - Voc is 20.23 volts and Isc is 6.25 amps.
Will 10g solar wire carry this as 12 volts about 8 feet from panels to SC? Or do I have to wire it up as 2s2p for 24 volts? The 10g wire is already installed thru the van roof and I’ve already received 1 to 4 connectors if I can go parallel but I can send them back to Amazon and buy branch connectors if I need to.
What I really need is to have someone make the decision for me so I can blame you if it all goes to hell in a hand basket. Please?
 

Don B. Cilly

Energetic energy padawan
On lead vs lithium... I've lived more than half my life on lead-acid. Quite happily.
Now, I finally decided to take a deep (financial) breath gasp and go lithium.
Half the Ah capacity I had. I basically... stopped worrying/suffering.

On 24V: it's my preferred voltage. I don't need 48 (or more) as I don't draw much. 12 doesn't quite cut it for most things though. It's sort of.. weak. On the availability of 12V vs. 24 "things"... my preferred workaround is, simple things like lights, fans and such, I just use them "in pairs". All my lights are 12V, I just wire two of them in series at a time. Fans, I do the same. Water pumps, easy to get at 24. And so on. If really needed, PWM 24-12 converters work really well. I have one. It's sitting in a drawrer ATM :·) 24 is quite easy actually.
 

12VoltInstalls

Solar Addict
it’s a cheap lithium vs a cheap lead battery
If that were the options I’d get the cheap AGMs. Cheap lithium at best, may work; at worst, may fail or cause a fire.
The cheap AGMs are a known quantity, low risk. Buy once every few years, maybe, whereas cheap lithium might involve some tears. What’s your risk tolerance?

As far as 24V, I have four 100W panels currently running 2S2P so 24V charging into fla 12V batteries. Runs fridge 24/7 without issue but it’s been dark, dark rainy for over three days now and I’m down to 12.2V, which isn’t the system’s problem and other than that it’s been a great setup.
12V isn’t ‘weak’ unless your trying to run big amps from an inverter or something. If one prefers 24V use it, or if the situation requires 200A+ battery draw or whatever 24V makes sense. In a 12V vehicle 12V is fine if it delivers the needs.
 

Smokin

Solar Enthusiast
Hook 2 100 watt panels in parallel. then to a charge controller. Do this twice.
Overall will be 2 200 watt systems.
Use AGM, the real Mans battery.
Dont need mppt. Just adds to much RF noise.
 

12VoltInstalls

Solar Addict
Hook 2 100 watt panels in parallel. then to a charge controller. Do this twice.
Overall will be 2 200 watt systems.
Use AGM, the real Mans battery.
Dont need mppt. Just adds to much RF noise
If that works for you great

In my opinion that’s a poor design given the specifics of the OP
Although PWM does ok for small systems, mppt does offer some advantages; agm can be a disadvantage in several aspects but it meets his needs for no maintenance whether it’s a man’s battery or not. (Personally: my battery choice has not effected my self image)
 

OldJimbo

New Member
OK, I made the decision. I’m going with the 2S/2P configuration and the mppt controller. I’m inclined to the Victron 75/15 but may need the 100/20 - only about $40 difference and people keep saying that it’s best to build in extra capacity. Don’t know if this is the right place to ask, but I’m worried about the temp suddenly dropping into the teens (F) while I’m sleeping in the house, then a crisp clear morning dawns and my batteries are toast. Should I just get a manual shut off switch for the solar positive and stop worrying?
 
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