AGM's, Charge rates, and wiring. Silly question, sorry

[Jules083]

Ok, I'm in the beginnings of figuring out my power system. Looking at getting a small AGM deep cycle and mounting it inside rather than making a big power bank outside. I just have a short bus and will likely only need power for a night or two at a time, so I can get away with a smaller capacity.

Here's my question/concern. Charging rates. If I put this battery inside the bus, with a 12 gauge wire ran through a relay hooked to the main starting battery, and this battery is mostly dead when I energize the relay, will I fry something? Or will it just all work together and charge itself in a normal fashion?

I will likely put a small solar panel on the roof eventually, but I was just thinking of maybe like a small 25 watt panel or something similar.

Here's the battery I'm thinking of getting:

https://www.amazon.com/AB12180-Patro...dDbGljaz10cnVl

[s2mikon]

What are you going to power off of this?

[Jules083]

Originally Posted by s2mikon

What are you going to power off of this?

Some LED interior lights, probably an LED porch light, Bluetooth receiver for maybe a few hours in the evening. Maybe run a small 12 volt fan for an hour or so if I need to cool the inside before bed. Nothing fancy.

[rffffffff]

It’s less than ideal I’m sure but I would feel safe doing that as long as you fuse the wire at 20a so the wire doesn’t burn and you limit the discharge of the battery to a reasonable level, like 12.0v, which you’re going to want to do anyway for the life of the battery.

You may be surprised how much a fan will draw and I think you may want a larger battery eventually but for the price of the battery it is probably a good learning tool even if you nuke it.

Seems like trashing your first set of house batteries is common and expected so starting small isn’t a bad plan!

[john61ct]

You need to know the maximum amps flow rate you need to accommodate

use BSS Circuit Wizard to size the wire, 20% higher

fuse to prevent going that high

Fatter wire if voltage drop is an issue, need to include the impact of your connectors, relays etc usually shoot for no more than 2-3% V drop.

Many AGM can pull at 1C but only briefly, usually drops to 0.8C then lower within a few minutes.

Good deep cycle AGMs in NA include Odyssey, Lifeline and Northstar. Call them for a local distributor, better than paying for shipping.

[Jules083]

Originally Posted by john61ct

You need to know the maximum amps flow rate you need to accommodate

use BSS Circuit Wizard to size the wire, 20% higher

fuse to prevent going that high

Fatter wire if voltage drop is an issue, need to include the impact of your connectors, relays etc usually shoot for no more than 2-3% V drop.

Many AGM can pull at 1C but only briefly, usually drops to 0.8C then lower within a few minutes.

Good deep cycle AGMs in NA include Odyssey, Lifeline and Northstar. Call them for a local distributor, better than paying for shipping.

Cool, basically I just need my wiring heavy enough to carry, for example, 12 amps to handle a 12 ah battery then I’ll be good no matter what? Easy enough, thanks.

[rffffffff]

Originally Posted by Jules083

Cool, basically I just need my wiring heavy enough to carry, for example, 12 amps to handle a 12 ah battery then I’ll be good no matter what? Easy enough, thanks.

Just make sure you put a fuse of the equivalent value in there so the fuse pops before the wires burn and you’ll be okay.