Battery charging

[Tractorat]

I've always disconnected the batteries in trailer, car, truck, etc when Ive hooked the batteries up to a battery charger. Not sure why, Ive just always done that. Someone probably told me to do it that way, and it seemed like a good idea.



Do I really need to disconnect the batteries ? After all, isnt the battery charger basically doing the same thing that the alternator is doing ?

 

[Skydiver]

Do I understand correctly? You unplug your camper/trailer from the truck when hooking up to 120v "shore" power.

 

[HBarlow]

There is no reason I have ever heard of to disconnect the batteries in a car, truck, RV, tractor, or any other machine when charging the batteries.

Yes, using a battery charger does exactly what your alternator does.

 

[LRutigliano]

I've always disconnected the batteries in trailer, car, truck, etc when Ive hooked the batteries up to a battery charger. Not sure why, Ive just always done that. Someone probably told me to do it that way, and it seemed like a good idea.



Do I really need to disconnect the batteries ? After all, isnt the battery charger basically doing the same thing that the alternator is doing ?

I do the same.



Electric battery chargers charge at a higher voltage than your alternator. Check out the voltage when charging and it usually will go as high as 15v @10amps. Your alternator is supposed to charge at 13. 8 to 14. 2 volts, but higher currents.



- In the truck, I disconnect the cables from both batteries and then charge them when needed. The truck has two batteries, so I don't know how you would charge them both with the connected to the truck.



- In the boat, I have a battery disconnect switch and I only charge the batteries when the switch is off.



I have two chargers and I charge them at the same time, but disconnected and isolated.



Both the truck and the boat are electronically fuel injected and have ECU's. I would not risk hooking up any charger to either rig with the ECU's in the loop...



Hope this helps,

Louis

 

[JLandry]

I never disconnect the batteries either. The electronics in your truck can easily handle 15 volts (if indeed your charger goes that high).



John L.

 

[HBarlow]

Both batteries will charge equally when connected in the truck and an external charger is attached because the batteries are wired in parallel ie both positive terminals are common and both negative terminals are connected together.

 

[Tractorat]

Well, the question actually has to do with my little MG. (probably should have mentioned that) The battery is behind the seat and is a pain to have to remove a battery cable. When I do charge this battery, I only see a high of around maybe 14. 2 volts checked with my hand held DVOM. The only electronics on this car would be the radio which keeps a little trickle going to keep the resets on the radio.

 

[Road Dog]

The only reason to disconnect the batteries is if there's another power source (like in an RV with shore power).

 

[Tractorat]

Thanks,

I knew that intuitively, but 40-50 years of habit has a strong influence. Never thought to question it.

 

[HBarlow]

I don't see any reason to disconnect the truck batteries when an RV trailer is hooked up and plugged in to shore power. Travel trailers have a converter which converts 115vac to 12vdc to power 12 volt accessories and charge the RV batteries.

When the trailer is plugged in to the truck the RV converter will also keep the truck batteries charged. If the additional load on the RV converter is not wanted it would be a lot simpler to simply pull the RV seven pin plug out of the truck to separate the two 12 volt systems.

I sometimes leave my trailer plugged into the truck when using shore power overnight simply because I forget to unplug the seven pin. If I stop for a quick lunch or quick supper and start the Onan generator in my fiver to run the microwave I don't disconnect. Running the generator is the same as connecting to shore power.

 

[Skydiver]

Some of the older RV chargers can boil the batteries dry in month. The newer units with the computer will back off the voltage when demand is low.

 

[jelag]

Louis... let me correct and add something to what you said...

Current to the batteries is based on the voltage... lets say that the alternator is set at 14. 2 volts and you have a battery charger set at 14. 2 volts. . if the connections have the same resistance than they (alternator or charger) will charge the batteries at the same current level... as the voltage increases on either the alternator or the battery charger they will overcome the bases resistance of the batteries and more current will flow... lower the voltage and less current will flow...

Think of the voltage as water pressure in a pipe. . more voltage, more pressure more flow. .

This is all a matter of ohm's law... simple math. .

BTW - no matter if I have the vehicle connected to shore power or a charger. . Understanding that if all the batteries are low (truck and trailer) it will just take longer to charge all of them... as your filling all the batteries to capacity...

Hope this helps understanding this. .

And what Skydiver says is correct... in fact a set of very low trailer batteries might not fully charge over night because the new design of the computers in the trailers might cut back the voltage (pressure) before the batteries are fully charged... and they sit there at below full charge... The technology is available to put a sensor at the batteries in the trailer and let it talk to the converter that keeps all this working... but those manufactures are meeting the demands of the trailer manufacturers (read cheep) so we don't see those controls... .

 

[gerry]

newer units with computer

Some of the older RV chargers can boil the batteries dry in month. The newer units with the computer will back off the voltage when demand is low.

do you have any idea when the change might have been made and how would I know if mine is the new type? My TH is a 06 BY Komfort

 

[Road Dog]

By "older RV charger", Skydiver means the '70s. In any case you should check the water level every few months in case the charger goes wild. Older chargers tend to be constant low current (trickle charge). Newer "smart" chargers monitor the battery and will fast charge when the battery is low and will cycle on and off once the battery is charged.

 

[Skydiver]

I sold my 1989 Newmar 39' 5ver that had the 30 amp charger. It would heat up a battery.
Look at a battery as if it were a sponge. The larger it is the longer it will take to charge and discharge. Never drop any battery below 12. 3 volts and it is even worse to leave a wet cell battery discharged for any length of time.
I bought this "smart charger" over a year ago for over $100. It is a battery conditioner meaning it delivers a voltage spike for a few mili seconds that breaks up sulphate crystals. Read all about it. Took me an hour of reading to fully understand how to operate it. It has paid for itself.
BatteryMINDer 12 Volt 2-4-8 Amp
More great reading about batteries.
Batteries -- and Other Electric Stuff by phred
gerry, I did read about the new camper chargers, but I can't recall it at this time. I think they were similar to the newer bass boat battery chargers.
Using your trucks alternator as a current delivering devise will make short life of it. Meaning don't use it to charge dead batteries. The regulator will over heat and burn out. Back before 1965 when vehicles used real generators you could hook up welding cables to a battery with the engine running and lay a row of dimes. Well almost. LOL

 

[HBarlow]

My '07 HitchHiker Discover America was factory equipped with a basic converter that overcharged the batteries. (I keep the trailer stored in my barn and plugged in all the time. ) I think it is an Atwood product. Before the trailer was two years old the batteries were both junk. I think most RV manufacturers use the cheaper Atwood or other basic converter. Some will overcharge the batteries as delivered and installed, some do not. It is the luck of the draw which one you get but it is an unsophisticated basic device.

I purchased and installed a new aftermarket controller that monitors battery condition and adjusts the charging rate. It has three or four modes of operation depending on battery charge condition.

Intelli-Power PD9245C 45A Electronic RV Converter/Charger

I actually installed the 55 amp version but the link shows and describes the 45 amp version. The new converter cost about $225 from an internet discounter and is a simple ten minute installation. Read the description and features and you'll see why many RVers replace their factory original with this product.

In addition to making a great product this company provides outstanding service. I had a question about some small part when I opened my box on a weekend and emailed the company. Within a few minutes I received a detailed reply from the company owner/president!

Comparing this converter/charger to the original is like the comparison between using candles or fluorescent lighting. No comparison. Try it, you'll like it. Standard disclaimer applies.