In-car charging both wet and AGM batteries

Gidday

we have AGM batteries that couple via a VSR..... from the standard alternator....... that is charging the cranking batteries.

Never had a problem in getting our AGM's charged...and our system has worked well for years...based in my experience I think you are being concerned over a situation that may be needless......

the biggest issue in charging is about choosing the correct cable size and relay...isolating solenoid....whatever else you choose for batery isolation when stationary.

Hi John

Yes I agree that the solar panels punch the charge in when compared to the vehicle alternator........we are also solar independant and rely heavily on them to bring the batteries up to capacity......... You should be getting 13.8v at least from your alternator however.

After an overnight camp or some overcast days followed by a days driving we have found that the amps pushed in by the vehicle alternator is less then therotical expectations....

on our camper trailer we have installed a Plsamatronics PL20 to control our solar input and battery management......we draw from 2 AGM 100ah batteries......we route the alternator charge through a shunt so as to allow the PL20 to monitor both the draw and either charge inputs (solar and alternator) ...in doing this the PL20 allows for battery amps in and out regardless of charge source..this is working well for us

regards

Hi again

yes our systems seem very similar.....the charge voltage of 13.8 is normal.....in fact my VSR is factory programed to kick in at 13.7 and out at 12.8......no means of changing the default...and I have verified these V with multi meters.

might pay you to check at the other end of the cables immediately prior to the auxillary battery input with a DC clamp meter for the amps and compare the reading to the display on your controller.... also multi meter at the auxillary battery end for V and see what you have happening

regards again

Hi John

First I think also that basically this shouldn't be necessary and if you have a modern alternator that isn't putting out 14v minimum on start up dropping to 13.8 when hot then problem is there.

The easy solution is to generate higher voltage cheaply.

To do this aquire a laptop car charger which cost 30-$50 from places like jaycar and come in 3 & 6 amp sizes.

assuming 6 amp version , set its output switch to 15v

I.E. with 12v input it will output 15v at 6amp , which is more than a 60w solar array.

Your AGM battery should be fine with 15v when driving the car,
and charge is not permanent. If your intend for permanent operation a 10amp diode in positive lead will drop volts of charge to around 14.4

An issue this cheap system is that if your battery is down then it will initially draw more than 6 amp and blow the laptop converters fuse.

A 1/2 ohm 10watt resistor in line with positive wire is usually all you need to solve this issue, or if agm is a long way away charging it via thin leads will often do. Your might need a little experimenting here so keep a couple of spare fuses , or if you provide details I could suggest best in your case.


Robin Miller

Simple solution IF you have an EXTERNAL (Alternator) Regulator is to replace it, (about $40) for a higher rated one, I'm not sure if it's the same for internal mounted regulators.

My 55 amp alternator now runs @ 14.4v at idle when initially charging the Calcium "Cranking" (5 yo DC27 Delkor Deep Cycle) battery, the 2 x 115ah AGM DC's never get below 12v, even when actually powering the fridge at night, so they never take long to recharge next morning under any conditions.
When the sun's shining and the fridge is running, there's more power going into the battery than being used by the fridge, so the battery is always fully charged till the sun goes down, unlike using a gennie, the AGM's only loose power when running the fridge at night.

The 2 x AGM DC's are charged by 200 Watts (~17v) of Solar power on the roof 24/7 via a 3 x stage solar regulator and they still read 12.7v just prior to the fridge starting up in the mornings, before the sun is up - when still almost dark, the fridge only runs 3 or 4 times a night for ~20 minutes.

Hi John and Val, as pointed out above, the first thing you need to do is have your alternator/regulator checked out.

For a while a number of vehicles were produced with alternator voltages that started out at something like 14 to 14.2 volts and once at operating temperature, dropped to around 13.8. This 13.8 is the minimum charging voltage needed for most batteries to be able to charge properly.

Newer vehicles are now being equipped with alternator voltage outputs of anything up to 14.7, with the average vehicle voltage being between 14 and 14.2, so your vehicle’s voltage is way below even the lowest charging voltage needed.

Next, unlike ordinary flooded wet cell and even the average gel cell battery where the info for one brand pretty well is the same for all other brands of similar batteries, every AGM battery is DIFFERENT and you must have the exact info for your specific brand and type of AGM battery.

Most AGM batteries are NOT specifically designed for automotive use but were originally designed for use in RAPS and UPS set-ups and as standby batteries for starting stationary generators.

As such, very few AGM batteries can tolerate more than 14.8 volts ( amongst other potential problems associated with using them in automotive applications ) so check out the info for your batteries as well.

Cheers.

My system works great.

I have 2 sealed lead acid batteries joined in parrallel for starting and running the "standard" stuff.

Then I have a 120a/h Fullriver AGM which is charged by an Arrid Twin Charger @ 20 amps. It's like a normal battery charger, but only requires 12 volts or so and "FULLY" charges the AGM.

Thank you everyone for your input. This is obviously a complex area. Your detailed comments indicate what a valuable pool of expertise and experience lies within this forum.

Thank you

John