ReCharging a 12 volt Deep Cycle AGM U1 Battery from Vehicle?

[DiploStrat]

Free Advice is worth ...

what you pay for it. So here goes:

-- You won't ever fully charge anything through a cigarette battery. But it may not matter.

-- If you are only going three days, and you don't have solar, simply put the battery on a shore charger between trips. If three days only draws it down to 12v, you should be fine.

-- Get some decently sized wire and tie the positive to the positive terminal of your starter battery and the negative to a good ground to your frame.

-- Put fuses at both ends and use your choice of isolation system - manual switch or ignition switch, for example.

-- Put some form of properly sized quick disconnect at the auxiliary battery side, so that you can take it inside to connect to the shore charger.

This way you get as much charge as possible when you drive and, assuming a good shore charger, still assure that the battery achieves a full charge between trips and remains on a proper float.

 

[wandererr]

So here's something to throw into the discussion I have a sizeable AGM battery in my trailer that gets charged from my tow vehicle .... wait for it..... Wrangle (2012). When the battery dropped to 11V, I was able to connect the jeep back to the trailer (I was in Sequoia and Yosemite setup for 3 days at each place) and bring it back up fairly quickly. Problems started when the power dropped to 10.4V. Even the long 12 hour drive (with stops and detours due to closures) did not get the battery to budge - I was stuck at 10.4V when I got home. It took some tricky recharge work with two different chargers to I think bring back my AGM battery back to life (it didn't want to hold charge after the first shore power recharge.

One of the potential issues is I think the wiring in the jeep. We have 168 AMP alternator BUT the wiring looks to be 10AWG at best. I believe that is 55amps max (not taking into account the distance). Granted - you might have bigger wire going from your battery to the trailer harness and to the trailer but still your alternator will only put out 55amps and you have other "on board" devices that need to run and you don't want to ruin your starting battery by it being the charging source....

Where does that take you? I am looking at what's called the "big 3" upgrade for the wiring in the JK. It involves thicker gauge wiring between the alternator and chassis as well as the battery to alternator. There are some issues with that as your original wiring has a fusible link that prevents you from blowing things up should the alternator go nuts BUT that can be addressed with a circuit breaker or another fusible link (something for you to research).

Where I am kicking myself is the fact that I knew the battery was dropping in power, but I figured - we're leaving tomorrow so I should be good to go.... end result? Fridge turned off because it didn't have enough power to operate the computer even though it is an LP fridge (it seems that the cutoff is at just under 11V).

So where does that take me? I am looking at couple things (being in similar boat to yours) - I am going to have a solar panel that I will be able to setup to get the battery recharged or at the very least slow down the discharge rate. I am also looking at making a "quick charge" wiring between the jeep and the trailer so that I can pull the jeep up to the trailer and have a short heavy gauge run from the alternator direct to the trailer in order to combat the power loss of long runs and to tap into the 168amps directly (or as close to 168 amps as possible due to the computer doing voltage regulation).

 

[DiploStrat]

Because I'm Feeling Crusty ...

... Problems started when the power dropped to 10.4V. Even the long 12 hour drive (with stops and detours due to closures) did not get the battery to budge - I was stuck at 10.4V when I got home. It took some tricky recharge work with two different chargers to I think bring back my AGM battery back to life (it didn't want to hold charge after the first shore power recharge.

11v is a paper weight. If you got it back, you got a freebie.

... One of the potential issues is I think the wiring in the jeep. We have 168 AMP alternator BUT the wiring looks to be 10AWG at best.

Which wire are you looking at? There is no way that that primary lead from your alternator to your starter/starter battery is 10 AWG.

... It involves thicker gauge wiring between the alternator and chassis as well as the battery to alternator.

Almost certainly not needed. The wire from the starter battery to the auxiliary battery may well be larger than the wire from the alternator to the starter battery.

... Where I am kicking myself is the fact that I knew the battery was dropping in power, but I figured - we're leaving tomorrow so I should be good to go.... end result? Fridge turned off because it didn't have enough power to operate the computer even though it is an LP fridge (it seems that the cutoff is at just under 11V).

So where does that take me? I am looking at couple things (being in similar boat to yours) - I am going to have a solar panel that I will be able to setup to get the battery recharged or at the very least slow down the discharge rate. I am also looking at making a "quick charge" wiring between the jeep and the trailer so that I can pull the jeep up to the trailer and have a short heavy gauge run from the alternator direct to the trailer in order to combat the power loss of long runs and to tap into the 168amps directly (or as close to 168 amps as possible due to the computer doing voltage regulation).

OUCH! Leaving tomorrow = at least 12 hours of draw and most fridges draw closer to 5A. At even 1 amp, that is 12Ah and, depending on the size of your battery, that could be huge. Again, recipe for paperweight.

Charging is never "quick". A surface charge will allow you to jump start a vehicle, but any full charge requires over two hours of steady charge, AFTER the battery is restored to full resting voltage.

You are never going to see 160A. The amount of charge that you see will be determined by the voltage of your charge source, in this case, your alternator. (14.xv is perfect), the size of your wiring, e.g. the resistance in the circuit, which rises as the amp flow rises, and, finally, the voltage of the battery. As your battery charges, its internal voltage rises and as the difference between the voltages of your charger and your battery decreases, so too does the amp flow, and thus the charge rate. This means that that first surface charge, so useful for a jump start, actually slows your long term charge. One reason that most shore chargers run overnight.

None of this is hard, it is merely complex and takes a few readings to get past all of the misinformation and misunderstandings.

Keep it simple and you will be very pleased with the results you get. Really!

 

[vtsoundman]

I have an 07 JKU. Does a fantastic job of keeping my underhood AGM at top spec. Got over 7 yrs from my last AGM...could get more if I left it and didn't drop it below 12 on about a dozen occasions....but when I pulled it and had it tested, I still have 60% or so capacity and the Jeep still fired up fin. I replaced it with a group 31).

Routinely see voltages in the mid to upper 14s at the cigarette lighter (unloaded - so no current induced voltage drop) and direct wired meter. Highest amperage recorded charging battery was 85A or so (maybe a bit higher) ... And I have the high output stock alternator unit. I have measured the alternator producing its full rating at speed however.

I run a CTEK 250s for my 2nd in cab deep cycle VRLA AGM...the battery has a much lower permissable charge amperage... limited to 30A. True deep cycle AGMs by certain mfrs have a much lower charge rate than the typical Duracell Sam's Club East Deka AGMs. I also wanted the integrated solar mppt. Well the CTEK doesn't do a great job at solar... I've quite a few comparisons over the past few weeks and the Victron 75/15 with a series panel config charges the battery bout 15-30% faster than the CTEK...and have recorded peak power solar of approx 20% more with the Victron. Per my other posting about the CTEK, it sweeps for MPP far too frequently in static solar conditions and /or drops into a low freq pulse charge before absorption is complete ( drops into pulse charge prematurely. )

I have also charged the same battery type in my trailer without the ctek. The voltage drop on the factory 7pin harness limits the charge acceptance to 30-35A. Not the most reliable means to limit charge current, but good enough for the price I paid for the battery.

sent via the cone of silence

 

[wandererr]

11v is a paper weight. If you got it back, you got a freebie.

I wanted to swap it out under warranty but since Amazon no longer carries it, they refunded my money and told me to deal with the carcass... so yeah - freebie

Which wire are you looking at? There is no way that that primary lead from your alternator to your starter/starter battery is 10 AWG.

I'm looking at the wire coming out of the starter. Maybe I'm eyeballing it wrong but it's definitely not thicker then 8.

Almost certainly not needed. The wire from the starter battery to the auxiliary battery may well be larger than the wire from the alternator to the starter battery.

If I'm wanting to charge the trailer battery from the alternator and run the trailer electrical from the alternator rather then pulling more from the battery then I need to allow for a higher current draw direct from the alternator. Don't know how to explain that better.

OUCH! Leaving tomorrow = at least 12 hours of draw and most fridges draw closer to 5A. At even 1 amp, that is 12Ah and, depending on the size of your battery, that could be huge. Again, recipe for paperweight.

Yeah, I'm not 100% trusting that battery... something is wrong.... will be checking it and adding a secondary battery since I got a freebie now

You are never going to see 160A. The amount of charge that you see will be determined by the voltage of your charge source, in this case, your alternator. (14.xv is perfect), the size of your wiring, e.g. the resistance in the circuit, which rises as the amp flow rises, and, finally, the voltage of the battery. As your battery charges, its internal voltage rises and as the difference between the voltages of your charger and your battery decreases, so too does the amp flow, and thus the charge rate. This means that that first surface charge, so useful for a jump start, actually slows your long term charge. One reason that most shore chargers run overnight.

I agree - I doubt I will ever see 160A but the original wiring is nowhere near close to be able to take advantage of the alternators capabilities. Why? Because if you take stock vehicle into account - it doesn't use that much. You have radio, your basic vehicle electronics and lights (plus the starter). So why spend money on bigger wires? I can tell you that the wiring on my XJ is significantly beefier then the JK wiring...

None of this is hard, it is merely complex and takes a few readings to get past all of the misinformation and misunderstandings.

Keep it simple and you will be very pleased with the results you get. Really!

come on.... there is always voodoo involved when it comes to jeeps

 

[DiploStrat]

Not having a Jeep handy ...

If you have a 150A+ rated alternator, you may be assured that the manufacturer oversized the wire to the battery. It may be relatively small if the run is short, but they don't want to be paying for failed/undercharged batteries. (In the case of my truck, each alternator was rated at 125A and the wires, less than a metre long, were fused at 175A. MY cables to the back were a pair of 1/0 AWG.)

… If I'm wanting to charge the trailer battery from the alternator and run the trailer electrical from the alternator rather then pulling more from the battery then I need to allow for a higher current draw direct from the alternator. Don't know how to explain that better.

Got, but it doesn't work that way. The starter battery is always in the circuit and that is good. (Get dwh to explain how circuits and busses operator.) You want to size your wire to the trailer for the distance to be run and the easiest place to attach it is generally to the positive terminal of the starter battery. You must also be sure that the ground/negative return spans the gap from the trailer to the ground of the vehicle; I would not trust the tow hitch.

For giggles, play with this: http://www.calculator.net/voltage-d...nce=15&distanceunit=feet&amperes=100&x=38&y=6

And do read the links provided in my previous post. They are simple slides.

 

[wandererr]

ok, so I might be reaching too far back in my mind to classes but there is more to this. Look at this link:
http://www.impactbattery.com/blog/tutorials/how-to-charge-marine-and-rv-batteries-in-parallel/

So if I go with just the stock setup and believe me - I looked at those wires couple times and they are not that thick, I end up with what I'm reading is an unbalanced setup. Part of the issue is that I'm going charger to battery, battery to battery. Having heavier wire from battery to the trailer makes that portion of the circuit also allow for more current to pass through between the two (consider also the distance). I see that running heavier wire from the alternator to the charging circuit and having it deliver to both batteries eliminates part of that (or am I off???). Now I won't be able to do the reverse setup so that the positive and negative get direct connection from the alternator starting at each battery opposite from each other.

Anyways - to a degree we are doomed because quite a few of us will be charging the battery as we drive from the alternator with a starter battery in parallel with the marine battery making this a suboptimal configuration.....

 

[DiploStrat]

… Anyways - to a degree we are doomed because quite a few of us will be charging the battery as we drive from the alternator with a starter battery in parallel with the marine battery making this a suboptimal configuration.....

Again, go look at my links. (I geek this stuff into the ground!)

Unbalanced charging is an issue WITHIN a single battery bank. You have two isolated banks which are only combined when under charge. Which, to answer you next question, is why it does not matter if they are the same size, brand, age, etc. This is only an issue when the batteries are permanently connected in series or parallel, as shown in your link.

You are worrying about a non issue.

Now, within my old bank of four 6V, 300Ah batteries, you may be assured that I had the batteries wired "diagonally."

I charged my Lifeline AGM deep cycle batteries, all 600Ah of them in isolated/parallel with two 75Ah lead calcium Delco starter batteries and the camper batteries were like new after years of use, including microwave, toaster, espresso machine, induction cooktop, refrigerator, furnace, and air conditioner.

To quote Julia Child, "If I can do it, you can do it, and here's how you do it!"

Best wishes!

More links from perhaps the best site on split charging (aka isolated/parallel) of lead acid batteries:

http://www.smartgauge.co.uk

This link is basically the same as the one you posted: http://www.smartgauge.co.uk/batt_con.html

None of this is new. just a bit misunderstood. (Great old song by The Animals, BTW.)