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Old 09-21-2020, 03:01 PM   #21
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Surprise!

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Originally Posted by Iggy View Post
If you have it hooked up to your truck charging system will go into high charge mode because it will sense a battery that is lower.
That is only if you have the trailer, plug and cable was properly wired.
Like I said teminal 4 wiring is the key if you have or don't have it wired already.
It was a surprise to me--hearing all the stories about slow charging from the 7-pin connector, to read the following in the Owner's Manual of the new-to-us 2015 GMC Sierra 2500 with "Heavy-Duty Trailer Package."
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If charging a remote (non-vehicle) battery, press the Tow/Haul Mode button, if equipped, at the end of the shift lever. This will boost the vehicle system voltage and properly charge the battery. If the trailer is too light for Tow/Haul Mode, or the vehicle is not equipped with Tow/Haul, turn on the headlamps as a second way to boost the vehicle system and charge the battery.
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Old 09-21-2020, 03:07 PM   #22
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Just for comparison

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Originally Posted by rsdata View Post
If you do in fact have a trickle charger, then it will do very little is a short period to charge the battery... a trickle charger will charge a lightly discharged battery in a day or more, but anything more needed will take several days of time. A trickle charger typically charges at 1 to 3 amps, which is fine if you have the time. Larger battery chargers will charge from 5 to 10 to 15 amps which reduces charge time to overnight or a day at most.

Assume your batteries are nearly depleted at the repair shop... ( do you have a cheap meter to measure the voltage of the batteries? $5-$10 at any hardware store. A fully charged battery is 12.6 to 12.7 volts ( measured after charger is off and battery sets unhooked for 3-4 hours). A discharged battery will be less than 12 VDC. If you hit 10.1 your battery will have lost some capability permanently.

take a picture of the connections with your phone, ( see diagram below) then take the batteries out and to your home and charge 1 at a time with something other than a trickle charger. You can get a 5 amp to 10 amp charger for $60 or less at Walmart or amazon. I found a good deal on one from amazon for you see below...

You probably have little to no charging capability from your tow vehicle to your camper, unless you know differently for sure. Often a fuse needs to be added to the TV to make it work.

You will have difficulty with electric 12 VDC power even for one night if you don't prepare ahead of time.
One of the most common converters in use in RVs is the WFCO-8955. True to its name, it starts off by providing 55 amps to a depleted battery. As noted by others, it tapers off as the battery becomes charged. (If it didn't, and raised its voltage to force 55 amps, the battery cells would boil over, splashing acid around and damaging the battery.)

For comparison, the trickle charger provides 1-4 amps. It's not worth bothering with.
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Old 09-21-2020, 04:18 PM   #23
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You are right and that's what I will do, thanks! This all will come in handy for future reference, though.

Of course, you received a lot of great information..
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Old 09-21-2020, 05:09 PM   #24
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I would disconnect the red and black wires that run to the trailer, then charge the batteries with a regular charger,, but first pull the caps and make sure all the cells are full of distilled water. If the batteries are totally discharged, the trailer and probably the truck also, could not bring them up. Gulf cart batteries can do that. They need an initial boost so the other chargers can pick up the slack. These batteries are used also, right? Once they are fully charged, you should have 13.5 volts measured while on the charger.
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Old 09-28-2020, 07:20 PM   #25
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Those of us with Solar would most likely have a charge controller
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Old 09-28-2020, 07:46 PM   #26
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I use multiple charging sources all the time. Sometimes I have my 10 amp charger on along with my Xantrex inverter/charger with my engine's alternator spinning. Not only that, but I also have 3 banks of batteries all connected by 2 VSRs.
For the purists, this might seem like a nightmare with their high tech multi-stage multi-bank equalizing chargers and expensive amp counters, but it gets the job done for me with minimum outlay and zero monitoring.


As for the OP's question about multiple charging sources, you might find this interesting - taken from the Yandina.com FAQ.


What happens if two alternators end up charging the same banks?
A Let's dispel the myths of multiple battery charging sources.
All a battery charger sees on the 12 volt circuit is a voltage.
It has no "knowledge" of what else is on there, charging or discharging.
It just responds to the voltage it sees at any one time.

1. If it is a dumb regulator or charger and the battery voltage it sees is less than its built in threshold, it charges at full strength governed by the difference between its internal voltage/source impedance and the actual battery voltage. When the voltage rises to the threshold, it stops charging. This process my cycle on and off at different speeds depending on loads, etc.

2. If it is a smart alternator or charger, then the above scenario is complicated by having multiple threshold voltages at which it changes from full charge to topping-off charge to maintenance charge, to off, however the underlying principle is the same. There may also be timers and temperature inputs that modify the thresholds.
So what happens when there is more than one charging source is all those regulators that see a voltage less than the (next) threshold, charge the battery as though the other charging sources weren't there. They don't "know" anything else is charging. During the bulk charge, when the battery voltage is below all the thresholds, all the sources will be putting out the maximum they can. As each charging source reaches a threshold it changes its charging rate accordingly. Since no two regulators will have exactly the same threshold(s) this means that some of the paralleled regulators will tend to cut down or shut down before others and leave the job of finishing the charge to them but by that stage the current requirements are within the capacity of the one(s) that continue(s) to remain on line.
Despite cries of doom, especially from outboard motor manufacturers, we have had customers using Combiners to parallel battery banks with multiple alternators and other charging sources since 1993 without a single feedback situation of any problems.
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Old 09-29-2020, 09:56 AM   #27
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Initially, I didn't think my onboard charger/converter was doing a good job, so I bought a Black and Decker 25 Amp charger. I found that when I used the external charger, my onboard charger would disengage as it was detecting a high voltage in the battery system. (It figured the batteries were fully charged) How did I know this? I have a Progressive Industries HW30C that monitors my electrical draw. As soon as the external battery charger was turned on, (plugged into external power) the internal electrical draw dropped.
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Old 09-29-2020, 10:12 AM   #28
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Originally Posted by jeffnick View Post
I use multiple charging sources all the time. Sometimes I have my 10 amp charger on along with my Xantrex inverter/charger with my engine's alternator spinning. Not only that, but I also have 3 banks of batteries all connected by 2 VSRs.
For the purists, this might seem like a nightmare with their high tech multi-stage multi-bank equalizing chargers and expensive amp counters, but it gets the job done for me with minimum outlay and zero monitoring.


As for the OP's question about multiple charging sources, you might find this interesting - taken from the Yandina.com FAQ.


What happens if two alternators end up charging the same banks?
A Let's dispel the myths of multiple battery charging sources.
All a battery charger sees on the 12 volt circuit is a voltage.
It has no "knowledge" of what else is on there, charging or discharging.
It just responds to the voltage it sees at any one time.

1. If it is a dumb regulator or charger and the battery voltage it sees is less than its built in threshold, it charges at full strength governed by the difference between its internal voltage/source impedance and the actual battery voltage. When the voltage rises to the threshold, it stops charging. This process my cycle on and off at different speeds depending on loads, etc.

2. If it is a smart alternator or charger, then the above scenario is complicated by having multiple threshold voltages at which it changes from full charge to topping-off charge to maintenance charge, to off, however the underlying principle is the same. There may also be timers and temperature inputs that modify the thresholds.
So what happens when there is more than one charging source is all those regulators that see a voltage less than the (next) threshold, charge the battery as though the other charging sources weren't there. They don't "know" anything else is charging. During the bulk charge, when the battery voltage is below all the thresholds, all the sources will be putting out the maximum they can. As each charging source reaches a threshold it changes its charging rate accordingly. Since no two regulators will have exactly the same threshold(s) this means that some of the paralleled regulators will tend to cut down or shut down before others and leave the job of finishing the charge to them but by that stage the current requirements are within the capacity of the one(s) that continue(s) to remain on line.
Despite cries of doom, especially from outboard motor manufacturers, we have had customers using Combiners to parallel battery banks with multiple alternators and other charging sources since 1993 without a single feedback situation of any problems.
For those less sophisticated in "electronics" it's more simple.

Think of a battery bank just like a tank of water. The charge sources are just like several water lines of different flow rates, each with a toilet tank float valve.

Water will flow according to the capacity of the lines (pressure, ID of line) until the float valves shut them off. The floats can all be set to shut off at different levels as well. When the float set for the highest level shuts off the "charging" stops.

Nothing "competes" or "fights back and forth".
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Old 10-01-2020, 12:34 AM   #29
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Separate the two batteries and then charge both at the same time then connect them back together before you leave. I am not sure the amperage that flows thru a TV/TT plug will charge a discharged battery in a day. The best way to quickly charge batteries via your TV is run big wiring to the rear bumper using trolling motor heavy duty plugs with a relay up by your battery then to your batteries.
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Old 10-01-2020, 07:10 AM   #30
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Your built in converter is a three stage automatic battery charger.

If you use the additional trickle charger it could interfere with the converters reading/automatic feature.

A trickle charger is 1-2 amps. The converter is 20-50/amps. A standard car charger is a fixed rate 8-10 amps. Not automatic. Slower than the converter!

So bring the unit home. Park in the driveway or on the street and plug the shore power in.

Likely you will have well over 80% charge the next morning when you leave.

At that point the 7 pin connector will provide a trickle charge to the tt to help while driving.

Likely two marine batteries would not power the furnace for two days. Maybe. You need about 200 amps likely. You have less than half that best case.

Since you will not be fully charged likely less. Plan ahead.
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Old 10-01-2020, 09:06 AM   #31
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Charge from Tow Vehicle

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Originally Posted by Fish N Farm View Post
Separate the two batteries and then charge both at the same time then connect them back together before you leave. I am not sure the amperage that flows thru a TV/TT plug will charge a discharged battery in a day. The best way to quickly charge batteries via your TV is run big wiring to the rear bumper using trolling motor heavy duty plugs with a relay up by your battery then to your batteries.
As noted elsewhere in this forum, to get a better charge while towing, turn on the tow-vehicle's headlights. This extra draw causes the alternator to charge at a higher voltage which compensates for the voltage drop in the cabling.
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Old 10-01-2020, 11:54 AM   #32
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As noted elsewhere in this forum, to get a better charge while towing, turn on the tow-vehicle's headlights. This extra draw causes the alternator to charge at a higher voltage which compensates for the voltage drop in the cabling.
That will only work on some vehicles. On mine headlights on or off makes no difference.

What I chose to do is invest in a $127 DC-DC Charger (Renogy DCC 1212-20) and even on he wimpy OE charge wires from TV battery to 7-pin connector I increased the charge current into my TT batteries 3X.

This allows one to recharge batteries more fully while driving from site to site rather than having to rely on a mere trickle charge.

I later upgraded the charge wire to #8 gauge and get a full 20 amp flowing into my TT batteries now. My batteries are LiFePo4's and are almost always fully charged when I reach my next site (boondocking). Lead Acid will take longer but at least there will be less need for additional charging once one arrives.

The DC-DC charger I purchased is essentially a multi stage charger that provides a bulk, absorption, and float charge for FLA batteries. In Li mode it just provides Bulk and Absorption charge.
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Old 10-01-2020, 09:53 PM   #33
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Going with the float analogy once you have one charger going the float is high for the second charger as the voltage is spiked by the charger, right? Its like running the dishwasher and trying to see how deep the water is in it... so likely only one will charge or if multi-stage they could both go to float which would slow the charge down right?

Doesnt solar get around this usually by using a BIM or in a pusher a BIRD and also the solar charge controller should account for some of this as well when combined with a converter.

Rather than have both batteries together and trying two chargers why wouldn't you remove 1 battery and charge it with your external charger and leave the other hooked up and charge it with the inverter? The inverter will likely charge the one battery faster and the scond could be done quicker as well. I am not sure if they would stay in bulk charge longer or shorter.

I guess if you don't fully charge them both there will be some time where they have to equalize and you lose a bit of charging time but that could happen on the drive via the TV alternator...

Just a thinking out loud. If I am wrong I am sure someone here will correct me.
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Old 10-01-2020, 10:09 PM   #34
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Going with the float analogy once you have one charger going the float is high for the second charger as the voltage is spiked by the charger, right? Its like running the dishwasher and trying to see how deep the water is in it... so likely only one will charge or if multi-stage they could both go to float which would slow the charge down right?

Doesnt solar get around this usually by using a BIM or in a pusher a BIRD and also the solar charge controller should account for some of this as well when combined with a converter.

Rather than have both batteries together and trying two chargers why wouldn't you remove 1 battery and charge it with your external charger and leave the other hooked up and charge it with the inverter? The inverter will likely charge the one battery faster and the scond could be done quicker as well. I am not sure if they would stay in bulk charge longer or shorter.

I guess if you don't fully charge them both there will be some time where they have to equalize and you lose a bit of charging time but that could happen on the drive via the TV alternator...

Just a thinking out loud. If I am wrong I am sure someone here will correct me.
You're overlooking the fact the battery is sucking up power and the incoming voltage doesn't rise until it reaches 80% or more SOC.
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Old 10-01-2020, 11:08 PM   #35
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You're overlooking the fact the battery is sucking up power and the incoming voltage doesn't rise until it reaches 80% or more SOC.
Ok. Would it be faster or slower to charge together or seperate with the same chargers and batteries then?
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Old 10-01-2020, 11:25 PM   #36
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Ok. Would it be faster or slower to charge together or seperate with the same chargers and batteries then?
The fact is that a flooded lead acid battery will only accept so much current at a given voltage. You could have 10 chargers on the batteries and if they are not sourcing their full current, its not going to really matter.


Flooded lead acid batteries can accept around 0.2C and no more.
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Old 10-02-2020, 10:14 AM   #37
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The fact is that a flooded lead acid battery will only accept so much current at a given voltage. You could have 10 chargers on the batteries and if they are not sourcing their full current, its not going to really matter.


Flooded lead acid batteries can accept around 0.2C and no more.
Agree and great information but most people would not be familiar with you're terminology refer to your charge rate around .2C. Being an former Electrician, as well as an Electrical Engineer for over 40 yrs. beside my FF career now retired, I do or maybe I should say I did so I dug up some old material to become acquainted with your information a little better as I'm start my Solar Quest for my DP so I'm looking into AGM, LifePo, Li-ion, and solar systems a lot lately. Anyway long story short I've attached a link to everything you might want to know about battery's for those who are interested, of course there's always more out there but it's a start. https://batteryuniversity.com/learn/article/what_is_the_c_rate. Thanks
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