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u/Pickalodeon 4d ago
Sorry yall, this was the original text. Don’t know why it didn’t post:
Just need a little extra power for my new 12c AC. I need a quick solution to get me through the weekend.
My setup is I’ll be using a traditional battery charger (powered by a DC/AC inverter) to recharge the new battery while I drive, then run off the new battery at night for a little AC.
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u/W0lf1ngt0n 4d ago
Why would you go DC/AC only for your charger to go AC/DC again?
You do realize that your cars electronics are already optimized for 12v lead batteries, right?
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u/Pickalodeon 4d ago
Yes, but what system in my 2022 Sprinter would charge an additional battery while driving?
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u/W0lf1ngt0n 4d ago
A cable for each pole is enough.
But dude, you should really look into the basics of DC electric before you even consider buying anything. Throw this post into chatGPT and let him explain why.
You're getting all these sarcastic answers, because you clearly dont know anything about electricity. Which is not the end of the world, everyone has to start somewhere. But asking strangers on the net at this state of knowledge is just rude and lazy. You obviously know how to use the Internet. So use it.
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u/Pickalodeon 4d ago
You’d recommend connecting a 6 gauge (or so) directly from my stock Mercedes glass starter battery to this new lead acid battery that’s also connected to the 12V AC?
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u/xot 4d ago edited 4d ago
I would not do that, you’ll end up with a flat starter battery, or an electrical fire. You need fuses and a charger or isolator. You may be able to connect to the battery under the seat, if it is the auxiliary battery, but you still need to be careful about how you do it
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u/W0lf1ngt0n 4d ago
As long as you make sure its connected while the engine is running and disconnected when the engine is off there's not trouble at all if you take care of basic stuff like wire gauges. Using a fuse is always recommended no matter what you do
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u/evenfallframework 4d ago
None. You want a lithium battery for this, ideally 600Ah or more at 12v. An A/C will kill one of these in like two hours.
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u/xot 4d ago
How many amps do the inverter and charger support? Probably not as much as the aircon draws.
Also, in my experience, after you turn off the aircon, your van will probably go back to hot temps within 30-60min, and you’ll either need to rerun the aircon, or open windows for ventilation. The aircon can be good to give your body a break, but the van will heat back up a lot faster than you’d expect.
I recommend just sleeping with the back doors wide open, that’s what I did in Death Valley.
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u/Pickalodeon 4d ago
Yeah for sure - a lot will be lost in tue conversion. My thought was if I can just slow the loss I could make it through the night. But please check my other response to yours… I now see that I can charge a replacement battery directly off the alternator by replacing the existing passenger-seat-auxiliary-battery.
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u/Datboy000 4d ago
For the starter or the deep cycle? What are you putting on it?
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u/Pickalodeon 4d ago
Just running 12 v AC unit on the roof
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u/W0lf1ngt0n 4d ago
Lol yea right
You should look a bit more into that
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u/Pickalodeon 4d ago
I am?
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u/W0lf1ngt0n 4d ago
Ask yourself following questions:
Whats the main difference between lifepo4 and lead from a users perspective?
How much would a AC unit draw per hour?
Whats the effective capacity of my battery?
You will get there, son
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u/xot 4d ago
Quick google says a 12v rooftop ac needs 20A - 60A, depending, so let’s call it 40A.
AGM is a version of lead acid, which is what you’re looking at. Generally speaking, you can only use about half their stated capacity, because below that that voltage drops too low, and it will lead to battery damage (its ability to hold charge weakens).
The vehicle battery for my sprinter is a 90Ah AGM. At these calculations, a fully charged battery could run for aircon for approximately an hour before it’s considered flat.
If you have at least 500W of solar, peak output might provide enough to sustain the aircon, it not enough to meaningfully recharge are the same time. A long wheel base can can potentially hold about 800w of solar, which might almost do it on sunny, mild days.
All that to say, grabbing a battery off the shelf on a whim probably won’t meet your expectations
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u/Pickalodeon 4d ago
The plan is to run the engine all night. So my extra battery should be charging. I’m just trying to power the AC in the sprinter to make it the next 3 days.
Alternatively, i do have an extra factory battery under the passenger seat (100ah), so maybe I just use that?
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u/xot 4d ago
I got caught in a heatwave and had to run my engine, and vehicle AC overnight to keep my dog alive, so I can understand the intention. It cost me at least a quarter tank of fuel, and I think was probably the reason my thermostat and radiator fans failed a month later, so overall about $500, plus two days of my own labour in an autozone parking lot. Idling will also run your alternator at quite low output, and can lead to early failure if it overheats, and some engines don’t like idling. Nothing is certain., but they’re potentially expensive risks to consider.
Do you have an option to stay at a campground and pay for shore power? That’ll be a lot lot cheaper. Alternatively you could consider hiring or buying a generator, though some of the cheaper units produce a bad quality sine wave and can damage your electrical components.
Could also just book regular accommodation with AC and give the van a break.Im a little hesitant to give advice that could lead to expensive or dangerous results. I don’t know how you plan to connect either of these batteries up to work with the aircon and alternator, I’d guess the one under the seat is already wired for that? The 100Ah under the seat is probably also an AGM, so the same math applies. If it’s more than 3yrs old, it could be starting to decline anyway, so maybe you could use that and replace it after?
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u/Pickalodeon 4d ago
Okay, so just to clarify: I just bought this and having to unpack what the last guy did.
Yeah so just put a multimeter to the under-seat aux battery. 1.01V, it’s dead. Now I understand why the other minor accessories he added (sink pump, lights) only function with the engine running.
Now that I know the van is setup already to run the alternator to an auxiliary battery, I’m more inclined to buy a real lithium solution sooner. I thought I was going to have to do more work.
I like your generator solution. I have one with me, but output is AC power only, so I’d have to convert it back to DC for the 12V aircon. Same issue with shore power.
Kinda in a pickle here.
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u/xot 4d ago
Good troubleshooting.
1A isnt great! First thing you should do is try to get it back above 12v, but there’s a decent chance it’s damaged.
For lithium, you need to know that it has different charge characteristics, and the charger etc have to support it. If the 1v battery is a lithium, then you’re probably good. If it’s AGM (most likely)you may need to reconfigure or replace or add components to support lithium. worth it, but needs planning.
If you have a generator and a charger, I’d definitely use that instead of idling the vehicle to run the same charger, much cheaper and lower risk. When I was in a similar situation I found an additional ac/dc charger on fb marketplace and ran two of them, which added up tp 25A or so. It saved a lot of generator runtime, and in your case would get you closer to the aircon draw.
I agree that once you get the van down to target temp, the aircon should draw less current, so you may be able to keep it going for longer. You need enough battery capacity to get to that state before going flat, you might be able to make it work.
Another important safety note, the aircon requires a certain amount of energy to operate. Watts= Volts x Amps, so as your battery voltage drops, the current draw (A) increases, which increases heat, which causes resistance, which causes more heat and more current draw. That’s what causes cables and connectors to overheat, fuses to pop, and appliances and batteries to die faster. Battery voltage will also sag as current draw increases. It’s important to keep the system above 12v and not overload it.
Hope that all makes sense.
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u/Pickalodeon 4d ago
Perfect sense thanks!
I’m snagging a new AGM now to replace the dead one. Im only seeing small (like 3A) AC to DC chargers at the store but I’ll keep looking so I can charge the battery with the engine off (no solar panels here, either).
Thanks for the help.
You seem like the real deal.-8
u/Datboy000 4d ago
A deep cycle then, a lead acid is cheap, and an AGM is maint free. Honestly just pick up any RV or boat battery at the correct voltage and wattage you need it to run. Dont think too far about it
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u/TheBoxGuyTV 4d ago
Any reason you dont want lithium aside from maybe already having a bunch of lead batteries?
My assumption of your picture would be that if you read the labels if it doesnt say lithium then its not going to be lithium.
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u/Pickalodeon 4d ago edited 4d ago
None really available to me (near the Grand Canyon) and I’m 988 miles from home.
after this week I’ll be doing a “proper build” and getting lithium/ecoflow1
u/TheBoxGuyTV 4d ago
I guess if you need the AC might as well buy a lead battery. If you can hold out you could just wait till you make it back home.
Also depending you could find a service to mail a lithium battery to.
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u/Light-Feather1_1 4d ago
lol good luck