Correct

Thats how they work, once the voltage drops the isolators cuts out to save the start battery from draining.

 

Here's an update.

I connected my trailer to shore power for a week prior to the Labour Day weekend getaway, and after that, it was hooked up to the truck for a 5 hour drive.

Using the same approximate draw as in July, I was able to go Friday evening to Monday morning on battery power with the battery meter showing 3 bars (out of 4) just before I hooked up to come home.

The fact that I didn't have to try to recharge using the truck even once is the result I was hoping for.

I guess the next question now is how far in advance I should hook up to shore power before I take it out on a trip.

 

If you are just trying to charge your battery, a stand-alone battery charger will likely be quicker than whatever's in your trailer. I use a 10/15Amp smart charger, and it usually settles down to charge around 11 amps. Still takes a while to charge that big battery, but only a few hours instead of days.

 

Now that's the result we'd expect. Remember that these two 6v batteries in series take a lot more charge time due to their size and capacity. Just expecting the truck to fully charge them is a mistake.

These are too big to get a good strong charge. The truck can't generate enough amperage through such a long and smaller 12-16 gauge wire.

Even your converter doesn't allow for a quick charge. They will charge at multiple stages starting at 14.2 volts.

However, you need both voltage and amps to complete a good charge. Neither of these can be expected to do this quickly with these big capacity batteries.

That's why they so much longer when using/discharging them.

Once you have them fully charged, showing 12.9-13.1v, keep a top charger or larger solar charger on them to keep them "topped off."

Otherwise, pull them and get a charger that will do the job right to begin with.

No more issues then.

 

I think you are going to see 4 ga. from the converters to the batteries and I would encourage checking the amp output on the charger in camper before deciding to rely on something else. I have not see a converter that will not "kick the butt" of any 15 amp portable charger and the algorithms they rely on pretty well mimic those found on the highest end inverter/chargers. Normally I see about 25-30 amp at the batteries using my Fluke clamp meter and have used WFCO deck mounts I carry on my truck when I need to rapidly charge chassis batteries in diesels. There I have seen right at 60 amps at the batteries.


As always my two cents worth,


Steve

 

Hey folks, here is a pretty guide guide to Battery living. The 12volt Side of Life (Part 1). I camp off grid a lot. Everything from 10 days at Texas Motor Speedway to 14 days in the Colorado Rockies and weekends and dirt track racing. Using 4 6 volt golf cart batteries. I have been doing this for years. First, do not depend on your truck to charge the batteries. That is a total mistake, with volt and amp meters you are only getting about 13.2-13.6 volts and maybe 10 amps per hour (the gauge of wire just cannot support much more). Secondly, do not discharge a Golf Cart battery to where only 20% of charge is left. Any other type battery, 50% is the max discharge on that battery. Third and most important, get rid of those hungry light bulbs that come in your camper and replace them with LED's. You batteries will last far and beyond as those hungry stock bulbs are pulling nearly 5 amps each of 12v DC. Turn on 4 of those hungry bulbs that is 20 amps coming out of the battery bank, with a 220 amp/hour battery solution, you have 10 hours of capacity to 100 percent discharge. That is not counting the LP detector and the other phantom drains going on. Also keep distilled water handy, charging boils especially when batteries are discharged below 50%. All in all, conservation when on batteries is the solution and it looks as the OP was more aware on the next trip as well as topping the batteries with a week worth of charge. I know as I keep track, that after a week at TMS, even using generators most every other day to charge, when I get back to the house and plug in the 5er, I watch the voltage (I captured a digital volt meter on a web cam for the duration) and it takes nearly 48 hours to charge the batteries properly. I have a 60 amp converter, and when the batteries are 60 percent discharged, it will start charging at about 40 amps into the batteeries for 12 hours at 13.8 volts and then as the voltage will goes slowly up to 14.6 or so, the amperage will go down accordingly to 2 amps. After 18 hours it will go into a high voltage desulfidization where the voltage is 15.6 volts for 8 hours, then back to 14.6 and 2 amps, then after 4 or so hours it then goes in to a storage mode of 13.2 volts and .1 amps. Now I am using a Progressive Dynamics PD9260 converter which is a 3 stage smart charger. As stated in another post, most if not all of the Convert/Chargers are 3 stage and some 4 stage these days. Again the link I supplied at the beginning is pretty good (and has pics) and will help tremendously understand DC storage for those that want to know.

 

Sounds like somebody has done their homework. It takes a long time to fully charge a lead acid battery, far longer than people expect. Take the time to understand what's required and they will give good service when needed.

What's important to note is that a charger should be "sized" to the battery being charged. When two or more batteries are in series or parallel it is electrically one big battery and this should be taken into account when selecting a charger, as they are not to be charged individually. Providing about 20% of the AH capacity (not CCA) is considered a nice easy, slow rate of charge. For a 100 ampere hour battery that's around 20 amps. Many retail chargers will not provide this. The rate is a balance between reasonable charging times, warping plates, boiling electrolyte excessively, etc. Also note that charge voltages are temperature dependent and cold batteries have higher internal resistance. While it is possible to overcharge a battery it takes dedication. Monitoring the charge voltage over time against published charts for the type of battery is also helpful in getting an idea of what's what. It pays to become familiar with battery maintenance.

 

The single overriding thought I have is to make decisions about charging based on data coming from your individual system. I don't anticipate casual users are going to devote a great deal of time or attention to their batteries. By the same token, my thought is there is much to gain by how batteries are used and cared.


Keeping them watered and no allowing them to deeply discharge increases longevity, are relatively simple things to do, and likely are of more benefit than putting in a high dollar charging system and neglecting the batteries, which I often run into in the large diesel pushers. Often doing the simplest things first gives the most "bang for the buck"


Steve

 

For those who want more focus on battery temperature, which is important, when it comes time to replace your converter, Parallax has pushed their TempAssure line of temperature compensating converters for several years. Parallax takes a very strong position that staged charging, by itself is not adequate to insure battery life, and the high-end inverters (Magnum, Xantrax) also adjust charging based on battery temperature.


Steve

 

This is great info as I had read of what these manufacturers are using as parameters. Technology seems to make our DC power more efficient and giving us an easier read on how to maintain our batteries. Temperature has such an affect on Batteries, especially in extreme areas of cold or heat. Staged charging is a step in the right direction, now adding the temperature as part of its logic in the converter computer is a logical step.
Even here in Texas I try to protect the batteries from the extremes of Temperatures. I wrap the batteries in insulation and then stuff insulation around the batteries in the boxes. Also if it is going to get Texas cold, 20's or upper teens, I usually plug in my 3 stage trickle charger until the cold snap is over. It may be overkill but I guess living in Missouri for 30 with pretty cold winters, I learned about cold and batteries a bit.

As back to the original post with the OP, long term charging of the batteries is the key. Plug in and let it charge for 2 or 3 days, I am just certain that the truck charging for 2 or 3 hours, you only put about 30 amps back in the batteries, if that on a dead charged battery, thats not much and your using a big motor to charge a little bit. Again depending on your converter/charger, it will take hours if not days to fully charge.
Also people may not realize is that if you have a 45 amp converter/charger, for example, is that if you are using your DC lights, appliances, or whatever, it is taking away from the 45 amps. So if you are charging a full 45 amps (or 10 amps from your truck) and then turn on a DC light bulb, you are now only charging 40 amps into your batteries, and the more you turn on, the less it will charge. Do not be fooled that you are charging full amperage and voltage when actually using DC power inside your rig. Its not 45 amps plus pull, its 45 amps and thats it. That is one reason I stepped up to 60 amps and now looking at the solutions that RV_Tech referred with temperature parameter monitoring.