How to charge 12V parallel batteries in an HDJ81

[finderscuba]

Rather than remove the batteries and charge them individually, I'd like to charge them installed. My googling has found that I should just hook up the 12V charger to one battery and let it do its thing. I would assume it would just take much longer, but that the batteries will equalize. How long will this take using a manual 10A charger? Last time I tried this the charger seemed to never finish its cycle.

 

[finderscuba]

Another question: can I install one of those 2A battery maintainers and connect it to the +B in the auxilliary power outlet box under the hood? Would this effectively maintain both batteries while the device is plugged in?

 

[sailor]

I would connect the + lead of the charger to the + post of one battery and the - lead of the charger to the - post of the other battery. Guarantees an even charge. Don't crank the engine with the charger attached in this configuration. I don't know if cranking and engaging the 12/24 start relay will hurt the charger.

 

[roalco]

I looked at that with one of the "intellegent" chargers and in the small print they said "not suitable for parallel battery installations".
I was always taught that charging batteries in parallel was not a good practice, and the LC is one of the only applications that I have come across that tries to make it work. And as we all know, to get decent life and capacities out of our batteries they need to be removed, cycled and charged independently, periodically.... As well as needing to be identical!

 

[roalco]

I would connect the + lead of the charger to the + post of one battery and the - lead of the charger to the - post of the other battery. Guarantees an even charge.

No, the batteries are still in parallel, and the one with the least internal resistance will take all the current. This is the big problem with parallel charging.

 

[finderscuba]

No, the batteries are still in parallel, and the one with the least internal resistance will take all the current. This is the big problem with parallel charging.

My research on the web indicated that it is fine to charge in parallel. If this is not the case, then how does the alternator charge the batteries in parallel in my truck?

Remember, these are 2 new batteries with the same datecode on them. They should be identical in internal resistance.

 

[z_power]

Last time I had to recharge simply disconnected one pole of "left" or USDS battery - then I could charge batteries one at a time without removing them from their cradles. Leaving "right" battery connected saved clock and radio settings.
If you're using one of today's automated battery chargers it takes the same amount of time as parallel charging - just need to switch cables in the middle (Q=I*t, Imax is charger dependant and almost constant).

 

[sailor]

Scuba wants to charge them in situ. If you hook both charge leads to say the right side battery, you will tend to charge it at a higher rate than the left. Charge current will take the path of least resistance (the right battery). I would prefer to have my identically date coded batteries charged in parallel, particularly if the current is so low like a maintenance charger.

 

[83bj60]

The path of least resistance is not the battery, but the thick copper cable. In any case this is irrelevant, the charge is voltage and chemistry/configuration controlled. In other words a larger battery will have lower internal resistance and take more charge than a smaller or weaker battery and as long as the voltage regulator limits the output at 14.4V, both batteries will end up charged indentically.

If it didn't work that way the alternator would not be bale to charge both batteries, however, it is completely another story when starting because at that time they are connected in series and the poorer battery will limit what you can do.

In other words, if one battery goes bad o the HDJ81, replace both and keep the other good one as a spare for emergency use and if you want to charge both batteries, simply connect your cables to one of them and make sure to unplug the charger prior to starting.

Of course, with large batteries, a 10 amp charge won't do much as this is more like a trickle charge or float charge Use a decent charger with a 20A charging setting and run for 5 to 10 hours, just make sure the batteries don't get hot, check the electrolyte density and stop when all cells have reached the same density, adding deionized water as needed.

If you are patient enough and keep watering the cells that have charged first to replenish electrolysed water while the poor cells desulphate slowly, over many days you can equalize cells of poorly balanced batteries.

 

[finderscuba]

Thanks for the advice.

I'm hoping that once my alternator is rebuilt, I won't have to worry about charging the batteries for quite a while

 

[83bj60]

Indeed, but beware of the Green Gremlins they've been staring at me since i did my last job last week when I had my coolant leak... I know, simply a matter of unbolting the cables, cleaning with a wire brush, lube with some silicone grease and put the stainless steel nuts back on... But I got other things to do... Like writing reports, answering posts, and trying to catch some sleep

 

[sailor]

Ahh. I am too lazy to swap the charger leads from one side to the other on a maintenance charge so I do 'em together. Understood. If you don't want to remove any truck primary wires do it my way. If you have a burning desire to remove truck primary wires do 'em individually. I like keeping things simple. And yes you can equalize, do peukerts equation and dance about in a tu tu singing showtunes whilst inserting your hygrometer in your tukus, but it is only a truck with a pair of rather small batteries after all!

 

[crushers]

two ways:
charge the first battery, when charged then move to the second battery and charge it. done.
or
go buy a cheap second charger and charge both at once. done.

the system will not know the difference.

Rather than remove the batteries and charge them individually, I'd like to charge them installed. My googling has found that I should just hook up the 12V charger to one battery and let it do its thing. I would assume it would just take much longer, but that the batteries will equalize. How long will this take using a manual 10A charger? Last time I tried this the charger seemed to never finish its cycle.

 

[83bj60]

Sorry, Wayne, but NEVER connect two chargers in parallel, unless they are fully manual, you'll blow up the control module(s). Ask how I know

Every once in a while, crappy tire and princess auto have specials on their low end 200A shop chargers (2/20/40/200), whihc you can then get for as little as $120. They work great, but they're bulky.

Otherwise get at least a top of the line 2/15/100 and connect it to one of the batteries. Anything cheaper /lower capacity is basically useless. Oh and the 100A setting will work, but it will cycle on and off every few minutes as it overloads, so it's basically useless for charging. The 15 A setting can be used overnight, it's unlikely you'll overheat/dry batteries at that setting when there are 2 identical ones connected in parallel like in our trucks.

 

[crushers]

okay, since i have never had an issue:
how do you know? i would love a good story...