Battery tender?

[GPS]

Hello. On my last trailer I always tendered with an external charger. I saw a recent thread on tendering by plugging in. Will the batteries charge and stay topped off with the battery disconnect switch disconnected or does it need to remain connected? Thanks for the help!

[Brian B-P]

The storage switch needs to stay connected, because it is between the power centre (where the converter-charger is located) and the battery. The storage switch is there to keep anything from running the battery down while in storage without shore power, but if you have shore power that's not an issue.

[HABBERDABBER]

Plenty of people leave the trailer plugged in, 24/7 in storage mode, with the switch in the ON position. No issues reported.

[John in Santa Cruz]

what they said, but it does also depend on your power center. the WFCO 89xx series (and hte PD46xx we often replace them with) are 'smart' 3 stage chargers that revert to a maintenance charge once the batteries are fully charged, so you're safe. The older Parallax and many other older controllers could boil batteries if left plugged in too long.

[GPS]

Thanks. I have a 2021. So keep the battery flowing to power the camper lights etc and plug it in. Glad I asked.

[rubicon327]

Originally Posted by GPS

Thanks. I have a 2021. So keep the battery flowing to power the camper lights etc and plug it in. Glad I asked.

Staying plugged in with the battery continuously on charge and kept at 100% assumes you have lead acid batteries. There was no mention of the type in the thread. I mention it because the strategy would be different if you opted for lithium.

On edit: I see from a previous post you have dual 6V lead acid

[John in Santa Cruz]

For long term storage of Lithium you actually want the batteries partially discharged, say 40-80%. ... I have yet to decide how to dump 1000 watt*hours from my 5000 WH lithium setup. Maybe shut off the converter and solar a few days before ending a trip, and let the compressor fridge run the power down

[alanerickson]

This ended up being the easiest for me after looking at a few different options. The angles are just some pieces I had laying around and I used them to make sure the bulb wasn't touching anything, especially the battery case.

[GPS]

Thanks. Yes. Sorry about that omission

[IanC]

Alan, I like your simple method, but how do you determine when you've hit the 80% sweet spot?

[alanerickson]

Originally Posted by IanC

Alan, I like your simple method, but how do you determine when you've hit the 80% sweet spot?

It's an 18w bulb and the current was right around 1.5A. So just run it for that many hours. Example 10 hours at 1.5 amps - 15 amp hours. So if you were at full charge (100Ah) battery, that would bring you to 85AH left in battery after 10 hours. Most meters let you measure current up to 10A, so just use the meter if you want exact current bulb draws. Read in series for current and make sure you're on the right meter terminals for 10A. I used this bulb. ~$3 for two. You could run two (or more) bulbs in parallel if you want to go faster.

https://www.amazon.com/PEAK-1141ll-b.../dp/B07NNTXJGD

And I did this after I pulled my battery because I can't disconnect solar and during the day it was charging. Already have a small breaker and I'm gonna fix that in the spring.

[John in Santa Cruz]

Originally Posted by IanC

Alan, I like your simple method, but how do you determine when you've hit the 80% sweet spot?

I have a smartshunt on mine, which measures current going in and out of the battery and tracks it as Watt*Hours

I just ordered a 200 watt 12VDC hair dryer for my wife, I figure that on for 5 hours will be 1000WH, which is 20% of my 5200 WH capacity.

[Centex]

Originally Posted by John in Santa Cruz

... I just ordered a 200 watt 12VDC hair dryer for my wife, I figure that on for 5 hours will be 1000WH, which is 20% of my 5200 WH capacity.

Not sure if you're joking (apology if you are) but it's highly unlikely that hair dryer is intended for a 5-hour sustained duty cycle, and the trailer wiring / socket where it's connected may not be up to a 5-hour sustained 16ADC load either.

Take care, there may be a fire risk related to that scheme. Personally, I wouldn't want to 'test' protective devices intended to avoid that, but YMMV.

[John in Santa Cruz]

I put a heavy duty cigar outlet in my aux power panel wired with a dedicated 20A fuse and AWG 12/2 marine wiring. it should be fine. and as long as the fan is working in the hair dryer, it shouldn't overheat

[Brian B-P]

Originally Posted by John in Santa Cruz

... and as long as the fan is working in the hair dryer, it shouldn't overheat

Not really. What does the hair dryer's owners manual say?

[edlynnrich]

Can you simply run the fridge on DC for whatever time it may take to drop the battery to its storage state?

Ed

[John in Santa Cruz]

Originally Posted by edlynnrich

Can you simply run the fridge on DC for whatever time it may take to drop the battery to its storage state?

Ed

yeah, probably. fridge specs claim average 500 watt*hours/day, so 2 days should bring the battery down sufficiently, with the solar shut off.

[edlynnrich]

Originally Posted by John in Santa Cruz

yeah, probably. fridge specs claim average 500 watt*hours/day, so 2 days should bring the battery down sufficiently, with the solar shut off.

Okay, good to know. I’ll keep that in mind when we put ours in storage next winter. Our delivery date jumped from August 5 to April 11. Didn’t expect that big of a leap forward. We’re super excited now!

Ed

[Hawkeye Ed]

Yes, storing a LiFePO4 lithium battery fully charged long term might reduce its life somewhat. In practice, that simply means to not leave it on even a trickle charger during winter storage as you would with a lead-acid battery.

Since LiFePO4 batteries self-discharge at around a 5% rate per month anyway, you'll probably never have to worry about reducing their life if they're fully charged and then disconnected when you put them away for the winter. Charge them back up fully in the spring and away you go!

[Ron in BC]

Originally Posted by alanerickson

This ended up being the easiest for me after looking at a few different options. The angles are just some pieces I had laying around and I used them to make sure the bulb wasn't touching anything, especially the battery case.

The running the battery down to discharge it is a blast from the past for me. My wife had one of the first cell phones available, think big version of the brick, and I made a cradle for it that connected to a light bulb. Each day she'd come home, run down the battery until the light went out and then charge it. How times have changed.

Ron