What voltage under load is 50% T-105's

Down 50% is at least 100 amp hours to charge. 8 amps will take 12+ hours of run time to get mostly charged.

8 amp (140 watt) solar panel might suit you well.

AllegroD wrote:
What charger do you have?

Yes, I'm boondocking..

I disconnect the batteries and use a batteryminder smart charger. Unfortunately the batteryminder's highest setting is only 8 amps.

One of these days I will replace my charger inverter. But I have a hard time justifying the cost since I haven't used my camper in two years after I blew up my cummins engine two summers ago on monarch pass and spent the next year removing and rebuilding it myself.

Now I remember, my charger takes a long time and all the unhooking etc.. I wish I would have replaced the charger inverter.

I went for a day and a half and only dropped to 12.38v with the fridge on.

What charger do you have?

2oldman wrote:

BFL13 wrote:
Also you can get away with several lower than 50% deep cycles with 6s, so no big deal if you do go down to 40% or whatever.

A 1.0v drop from just watching tv/receiver seems excessive to me. If RJ does this on a regular basis, that can't be good. I don't know what reason there could possibly be for doing that.

3 guesses, the right one being, I didn't do it, it comes under "stuff happens", probably because the wiring is too light on that circuit. Its always been that way, doesn't hurt anything, don't know why it ever would. Inv alarms at 10.5. It is slightly inefficient for sure. I never fret much about voltage drop. Its a normal thing on 12 volts. Another voltmeter shows the batteries are getting 14.4 when charging, or what ever the PD gives them when I'm not looking.

This thread was actually how to determine when to recharge. I have it figured out on my RV. Others will be different. There is no fool proof shure fire way,.....except a system monitor ?? I myself don't need one

Hydrometer one cell. End of guesswork matching state of charge to voltage. One shot is plenty. One time first thing on one single morning. Ends the utter guesswork.

rerod wrote:
I charge daily but wonder if I'm using more than 50% per day.

Considering the described light usage I have serious doubts you are using 50% each day.

If the battery is getting below 12.4 each day your converter is probably just slow charging the battery and needs an upgrade. You need to be charging at 14.2+ volts to get a decent charge in reasonable time.

Get a battery monitor like a Trimetric, install it properly, and learn how to read it. Just a friendly suggestion.

I believe he is BOONDOCKING and wondering when to start the generator to recharge the batteries.

rerod wrote:
I have two trojan T105's for my toyhauler.

For the most part, my norcold refrigerator is the only load , other than a occasional light in the bathroom and the water pump. We use flash lights allot after dark and usually go to sleep then.

With the norcold as the load, what voltage measured at the battery terminals would indicate they are at 50% capacity and need charged?

I charge daily but wonder if I'm using more than 50% per day.

Thanks

It sounds a lot like you have a converter in your trailer that doesn’t have a smart three stage charger built in. You battery is never fully charging because the converter voltage is at the minimum. You might be able to add the charge wizard to you converter.
MM49

It seems to me it is pretty hard to get an accurate state of charge from voltage readings due to the artificially high voltage for hours after any charging. A better solution is a battery monitor that can show how many amp-hours below full charge the batteries are. This works by continuously integrating the current over time. I have a cheapo $25 one from China via eBay that works well, showing amps charging/discharging, % of full charge as well as amp-hours.

We just did a full week of boondocking with no generator. The 100 watt solar panel plus some engine charging while driving a little several times left us at 90% charge at the end of the week in early afternoon.