Continuous Duty Solenoid and AGM Batteries

[Mobile Mike Sutton]

A little help please!  I appreciate the wealth of knowledge and experience available here.  Hope to give back one day!

I've been gifted 2 100 Ah AGM batteries.  I won't be financially able to install solar for 4-6 months.  I'm in the process of building out my '93 G20 and have been researching continuous duty solenoid installs via blog's and videos available.  I've come to understand that the way 'flooded' lead acid and 'AGM' batteries should be charged is different.  Will using a continuous duty solenoid as a way to maintain the charge on my 'House AGM's', for that 6 month period damage them?  Is there some way to charge them properly via a continuous duty solenoid?

I'm nearly ready to do some fall national forest camping and explore what I want and need to have to go full time. 

Thanks in advance!

 

[DannyB1954]

Until you have a solar set up, (and on cloudy days even if you do have solar), you will need a way to recharge the batteries. A continuous duty solenoid will work well provided you drive every day. It can take hours to recharge 200 amp hours of batteries, so I would also recommend a small inverter generator like the Honda or Yamaha 1,000 watt type. You can then run a 40 amp charger anytime that you want.
I personally went with a 900 Watt Roybi propane generator. It only puts out 700 Watts continuous, so a 40 amp charger will cause it to overload at full charge. I carry a 25 amp portable charger to use with the generator.
I also have plenty of solar, so the generator is really only there as a back up.
The very worst thing you can do to any lead acid type battery is drain it low and then let it sit for days before recharging.

 

[Mobile Mike Sutton]

Until you have a solar set up, (and on cloudy days even if you do have solar), you will need a way to recharge the batteries. A continuous duty solenoid will work well provided you drive every day. It can take hours to recharge 200 amp hours of batteries, so I would also recommend a small inverter generator like the Honda or Yamaha 1,000 watt type. You can then run a 40 amp charger anytime that you want.
I personally went with a 900 Watt Roybi propane generator. It only puts out 700 Watts continuous, so a 40 amp charger will cause it to overload at full charge. I carry a 25 amp portable charger to use with the generator.
I also have plenty of solar, so the generator is really only there as a back up.
The very worst thing you can do to any lead acid type battery is drain it low and then let it sit for days before recharging.

Thank you DannyB1954.  I understand that for the solenoid to fully recharge would require lots of miles.  The answer I can't seem to find is whether or not charging in this manner will  shorten the life of AGM batteries.

 

[tx2sturgis]

You could end up spending $100 on a solenoid and the heavy cabling needed, or you COULD spend that $100 on a minimal solar controller (compatible with AGM) and a small solar panel.

What you didn't mention was: what will you be powering now with these batteries, if anything?

If you just need them to be maintained and fully charged, for now, running only minimal loads, (daily laptop charging, phone charging, an LED light or two) then a small 50-75 watt panel and an inexpensive PWM controller will be able to keep them fully charged.

No, the solar power output wont balance out a heavy power drain such as a 12v fridge or an inverter running a microwave, but you will be able to keep them charged and healthy, with no driving around needed....think of the gas you will save if you just want to camp somewhere for a week!

 

[jonyjoe303]

AGM batteries liked to be charged at high amps, they will actually last longer getting charged from the alternator all the time. At 14.4 volts the battery will start taking less amps when it starts getting full, no way to overcharge it at the voltage the alternator puts out. Even if the alternator can put out 100 amps, the battery only takes what it needs. 

To damage the battery you have to charge at over 15 volts which will force the amps into the battery, this will cause it to vent. And undercharging the battery will kill it quickly, never let it go below 12.1 volts. AGM's aren't true deep cycle batteries like golf cart batteries that can be abused.

Solar panels even a large one will at most trickle charge a 200 ah agm battery bank. That why the solenoid is preferable to fast charge the battery. When on solar I always floated my AGM at 14.4 volts for years, it liked that voltage. Trickle charging at less then 14 volts is only for long term storage. And some AGM's actually prefer higher voltage then 14.4 volts, but the mfg manual will tell you, but 14.4 volts is a good safe voltage.

 

[MrNoodly]

Aren't most vehicle batteries AGM's these days? Sealed and all that? Perhaps we're actually talking about the differences between starter and deep cycle AGMs.

 

[John61CT]

Charge sources should be profiled for the larger House bank.

Keeping the cheap Starter batt topped up is trivial, NBD, no need for precision there, an Echo charger will do it.

 

[wayne49]

Aren't most vehicle batteries AGM's these days? Sealed and all that? Perhaps we're actually talking about the differences between starter and deep cycle AGMs.

OP has a 1993 Chevy G20. 1993 days may be different from these days.

 

[Mobile Mike Sutton]

AGM batteries liked to be charged at high amps, they will actually last longer getting charged from the alternator all the time. At 14.4 volts the battery will start taking less amps when it starts getting full, no way to overcharge it at the voltage the alternator puts out. Even if the alternator can put out 100 amps, the battery only takes what it needs. 

To damage the battery you have to charge at over 15 volts which will force the amps into the battery, this will cause it to vent. And undercharging the battery will kill it quickly, never let it go below 12.1 volts. AGM's aren't true deep cycle batteries like golf cart batteries that can be abused.

Solar panels even a large one will at most trickle charge a 200 ah agm battery bank. That why the solenoid is preferable to fast charge the battery. When on solar I always floated my AGM at 14.4 volts for years, it liked that voltage. Trickle charging at less then 14 volts is only for long term storage. And some AGM's actually prefer higher voltage then 14.4 volts, but the mfg manual will tell you, but 14.4 volts is a good safe voltage.

  Thanks jonyjoe303 !  I think this is the info I was looking for.  It was nice to get a couple of free Batt's to learn the in's/out's of vanlife power generation on.  I've read a bunch of vet's who say we newbies will likely kill the first set of Batt's we have.

 

[highdesertranger]

under charging or over charging will shorten the life. with a solenoid you are more likely to under charge. you need to do an energy audit and let us know the numbers. highdesertranger

 

[Mobile Mike Sutton]

Thanks highdesertstranger,

Nothing to audit at this point. I was gifted these batteries prematurely and likely won't be using them until spring. I was merely trying to insure that I wouldn't destroy them by charging via solenoid.