diy solar

diy solar

12v vs 24v

PS I’m assuming the 100/20 lacks cold temp shut off, since the Victron website doesn’t seem to say.
 
Should I just get a manual shut off switch for the solar positive and stop worrying?
I missed where you decided on lithium

If I didn’t and you’re buying the AGMs they won’t care about the temperature too much.

The victron should have a set-able low-voltage cut off build in
(If I got your point correct)
 
Yes, say you can get 300W out of the panels, at 25V it's 12A.
Say you get a solar flare when parked on a hill ;-) and get a bit more.
For $40 difference, get the bigger controller. It's usually not a good idea to use something continuously close to its limit.

About temperature. A simple thermostat would do the job. If it doesn't take the amps, just use a relay.
With two-way switch on it... you could... divert the solar power to a coil under the batteries, on those cold sunny mornings, it would heat them instead of charging them. Until the thermostat switched, while you're comfortably sleeping/doing other things.
 
PS I’m assuming the 100/20 lacks cold temp shut off, since the Victron website doesn’t seem to say.
The spec sheet states that it does have an internal temperature sensor (it actually says all of their charge controllers have it) and running Victron Connect against a demo 100/20 shows the option for cold temp shut off for LiFePO4 batteries.
 
Wired it as 2s2p so I’m about at the “buy batteries” point. Why is a 24v 100 ah battery so much more expensive than two 12 volt 100 ah batteries? I’m seeing about 10 to 20 % difference in these prices in lifepo4. Which brings up another question. Because of the zero degrees C charging equals disaster issue, I seem to have a choice of BattleBorn or generic (cheap) batteries with expensive Victron SC.
Why not ignore lithium and go back to a quality AGM lead-acid? Maybe buy the Victron 75/15 with fla? I keep reading reviews which lead me to question my previous decisions (there lies madness, lol).
 
Why is a 24v 100 ah battery so much more expensive than two 12 volt 100 ah batteries? I’m seeing about 10 to 20 % difference in these prices in lifepo4.
Which battery? I've seen cases where a 24V 100Ah battery is cheaper than 2 12V 100Ah batteries from the same company. SOK is one example. A Battle Born 24V 50Ah is well under the cost of two 12V 50Ah batteries and also cheaper than a 12V 100Ah.

with expensive Victron SC
Expensive? The 100/20 is only $157.

Why not ignore lithium and go back to a quality AGM lead-acid?
This is for a van, right? LiFePO4 is smaller and lighter for a lot more usable capacity. It's also cheaper in the long run due to the number of cycles you can get. But you do need to deal with avoiding charging when the batteries are close to freezing.

How often will your Van get below freezing while you are still trying to charge the batteries? What about your fresh water at that point?
 
Why not ignore lithium and go back to a quality AGM lead-acid? Maybe buy the Victron 75/15 with fla?
“Quality AGM”
Under steady use, the cost over lifespan is sorta expensive imho. Even for offroad winching: lots of folks swear by their expensive sealed battery but in my observation of people who frequently use their recovery winches: certain inexpensive commodity fla’s often outlast the expensive battery guys.
But I can see the attraction to AGMs for use inside a van or home.

In your case, a “quality” AGM is what? $350/$500? How much? Compared to lifepo is how much? And consider 100Ah labeled of agm as 45-50Ah TOPS of useable and 100Ah of lifepo is 95-100Ah usable.
How long (or short) of a time period will you accept for service life?

If low upfront dollars make sense for you for the lead acid and you don’t have issues with replacing in a few years I guess AGMs work
If you don’t mind the upfront dollars: on a fifteen year plan buy good lifepo.
If you will regularly fully use most or all useable battery watts, and/or need more than 400-760W of solar lifepo starts making more and more sense. If you need more than ~400Ah+ of usable capacity daily or a 1200- or 1500W inverter is not enough….

You get the picture I hope.

Those are the kinds of things I’d consider if weighing any Lead Acid battery VS LiFePo, but at the expense of AGM the cost accounting is probably more important
 
Personally, I would only consider lead acid for the use cases where LFP is contraindicated.

Sadly, as an AGM fan, I have to agree with that statement. There are only a couple instances where AGM is a better decision than LFP's, but those few use cases are important.

1: You can afford a solar setup OR LFP batteries, get the FLA's and upgrade later.
2: Your battery compartment is located somewhere that gets below freezing on a long term basis, like my camp that gets below freezing for weeks to months straight and isn't attended, LFP's just don't work.
3: When you're really worried about reliability and the options are 6 months wait or 2 hour drive to replace batteries.

LFP's are better in most ways, just not long term cold or up front cost.
 
True, but my point is that FLA's are a great way to cut up front costs when you're working on a budget. AGM's are still much cheaper than FLP's though up front cost.

Also:
Also Please provide a product link to a quality AGM lead acid battery.
Challenge accepted :p 48v 60 usable Ah of AGM = $1480, 48v 60 usable Ah of FLA = $352

Return challenge: please provide a product link to a 48v 60Ah LFP within 100 miles of Ione, WA for about $1500. FLA's and AGM's are about 50 miles away for reference.

Hence the paranoia aspect of AGM's or FLA's. :)
 
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True, but my point is that FLA's are a great way to cut up front costs when you're working on a budget. AGM's are still much cheaper than FLP's though up front cost.

Also:

Challenge accepted :p 48v 60 usable Ah of AGM = $1480

Return challenge: please provide a product link to a 48v 60Ah LFP within 100 miles of Ione, WA for about $1500. FLA's and AGM's are about 50 miles away for reference.

Hence the paranoia aspect of AGM's or FLA's. :)

Not what you asked for but a good source https://www.currentconnected.com/contact/
Its about a 1000 miles but I'm sure @HighTechLab can ship to you.
 
Sadly most of my use cases are just not LFP friendly between it being so cold for so long and the need to be able to go into town and get new batteries right now if anything goes wrong.

In a few weeks I'm going to be rebuilding my entire system (Show & Tell pics coming) and using FLA's because I can get them now and within budget-ish. My other option was to not have power at all for the 3 years it would take me to afford the whole system AND Lith batteries... sooo, having the FLA's lets me have heat and lights now.

Plus the whole cold & unattended thing.
 
OK, I’m ready to order the battery. I think a 24 v 100 ah Ampere Time will be best because it will be enough to handle what I need now and I can connect another one in parallel if my needs increase later. I’m hoping someone will tell me if I would be better off with two 12 v batteries in series - especially since I’m still ignorant as can be about the potential pitfalls. I’m glad Will thinks that an Ampere Time with a Victron 100/20 SC will be a good inexpensive combination which still gives low temp charging protection. Later I can add a shunt if I need it. At least with the battery here I can start building the interior of the van.
All comments are appreciated, especially since I won’t pull the trigger until this evening, lol.
 
OK, I’m ready to order the battery. I think a 24 v 100 ah Ampere Time will be best because it will be enough to handle what I need now and I can connect another one in parallel if my needs increase later. I’m hoping someone will tell me if I would be better off with two 12 v batteries in series - especially since I’m still ignorant as can be about the potential pitfalls. I’m glad Will thinks that an Ampere Time with a Victron 100/20 SC will be a good inexpensive combination which still gives low temp charging protection. Later I can add a shunt if I need it. At least with the battery here I can start building the interior of the van.
All comments are appreciated, especially since I won’t pull the trigger until this evening, lol.
Incidentally, I got 33.9 volts from the 2s2p panels late yesterday afternoon, so that seems OK.
 
OK, I’m ready to order the battery. I think a 24 v 100 ah Ampere Time will be best because it will be enough to handle what I need now and I can connect another one in parallel if my needs increase later. I’m hoping someone will tell me if I would be better off with two 12 v batteries in series - especially since I’m still ignorant as can be about the potential pitfalls. I’m glad Will thinks that an Ampere Time with a Victron 100/20 SC will be a good inexpensive combination which still gives low temp charging protection. Later I can add a shunt if I need it. At least with the battery here I can start building the interior of the van.
All comments are appreciated, especially since I won’t pull the trigger until this evening, lol.
Do the ampere time batteries support being connected in series?
My cursory investigation of their website only shows parallel connections.
 
Yes. On Amazon, under the 24v, 100ah listing, they say you can connect 4 in parallel and 2 in series.
 
Yes. On Amazon, under the 24v, 100ah listing, they say you can connect 4 in parallel and 2 in series.
A single 24 volt battery will be the easier to integrate.
You would need a 12 volt charger to top balance the 12 volt batteries before you connect them in series.
Plus the wire and lugs to connect the 12 volt batteries in series.
I vote for the single 24 volt battery.
 
After reading about the Weize low temp disconnect 12v 100ah I looked on Amazon and found them at $464 each. Damn! A day late and a dollar short, that’s my motto.
 
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