Charging AGM batteries (via split charger) in a car

[CompoSimmonite]

I understand AGM batteries need some sort of special battery monitor or whatever when charging so I can't simply use a split charger in a car .
How, therefore, do I charge a AGM battery in a camper conversion ?
Cheers.

 

[hotponyshoes]

Search for DC DC Charger

 

[voipio]

There is very little difference between the recommended charge voltages for AGM and flooded lead acid batteries. AGM are reckoned to need around 0.3V higher for bulk charge, and about the same (13.6-13.8V) for float charge, so really no special charger needed. However, the so called smart charging systems in modern cars can take the main vehicle battery up to 15.5V or thereabouts, at times, in order to dump charge into them faster, which may no sut the AGMs so much, in which case a DC to DC charger would be better.

 

[m_c]

DCDC is nearly always better for split charging, regardless of the battery type.

As has been said, AGM isn't that much different in terms of charging voltages, and will quite happily operate as a direct replacement for conventional batteries, however when they're suitably flat, they will extract every ounce of power possible from the alternator, which is why they're not really recommended as a replacement on older vehicles with basic alternators.
They can also be charged at a higher voltage to get them to charge even quicker.

What vehicle are you converting?
If it's got any kind of smart charging (some vehicles have had Smart Charging for 20years), then you have to consider where it's connected.

Also, for a new conversion, I'd seriously consider LiFePo4 as an alternative, as they give better performance, last longer, and aren't that much more expensive now for comparable Ah. However they don't like sub-zero temperatures.

 

[carbon]

I use a Ctek dc to dc charger in my van to charge an agm battery that runs my night heater and interior lights etc. The agm battery has just been replaced after about seven years

 

[CompoSimmonite]

DCDC is nearly always better for split charging, regardless of the battery type.

As has been said, AGM isn't that much different in terms of charging voltages, and will quite happily operate as a direct replacement for conventional batteries, however when they're suitably flat, they will extract every ounce of power possible from the alternator, which is why they're not really recommended as a replacement on older vehicles with basic alternators.
They can also be charged at a higher voltage to get them to charge even quicker.

What vehicle are you converting?
If it's got any kind of smart charging (some vehicles have had Smart Charging for 20years), then you have to consider where it's connected.

Also, for a new conversion, I'd seriously consider LiFePo4 as an alternative, as they give better performance, last longer, and aren't that much more expensive now for comparable Ah. However they don't like sub-zero temperatures.

The batteries are brand new and originally bought for my mobility scooter but now I've decided to use them in a basic conversion of my Fiat Doblo. I have Sleep Apnoea so need to run a CPAP machine at night which will be main usage. Plan is to run a battery cable to the rear interior with Anderson socket so I can jump start other vehicles, power a winch on my trailer / drag mobility scooter up ramps into the Doblo, power a 12v microwave (a Wavebox) - all with engine running. The idea is to plug the AGM charger into this Anderson socket only when needed. One thought is I already have suitable AGM mains charger so, in theory, I could simply use that - via a small inverter that I've already got.

 

[hotponyshoes]

If you already have an agm charger and an inverter then you could use that just for the cost of an extra anderson plug.
It's not particularly efficient stepping from low voltage dc to high voltage ac then back down to low voltage dc again though.

Personally, I'd just spend the money on a dcdc charger then if the van has been parked up for a while and you finally go away the leasure battery should be charged when you arrive.
Safes faffing about plugging things in and turning them on/off plus you can get additional functionality like a solar panel input and a voltage display.
Some even link to a phone app or have power monitoring (capacity remaining) built in

 

[CompoSimmonite]

If you already have an agm charger and an inverter then you could use that just for the cost of an extra anderson plug.
It's not particularly efficient stepping from low voltage dc to high voltage ac then back down to low voltage dc again though.

Personally, I'd just spend the money on a dcdc charger then if the van has been parked up for a while and you finally go away the leasure battery should be charged when you arrive.
Safes faffing about plugging things in and turning them on/off plus you can get additional functionality like a solar panel input and a voltage display.
Some even link to a phone app or have power monitoring (capacity remaining) built in

The camper aspect won't be permanent and my Fiat Doblo MPV will be used most days as any other vehicle.

 

[Misterg]

I believe the 2020 onwards Doblo has a smart alternator. I don't know how Fiat run theirs, but the Ford ones reduce the charging voltage when cruising around and aim to keep the battery at less than 100% charge so they can dump power into them on overrun / engine braking (and send the voltage really high in the process). If Fiat do the same, then it possibly wouldn't charge your AGMs effectively - indeed they may end up running the car.

Summary here:

Aux Battery Charging With Smart Alternators | 12 Volt Planet

A guide to the benefits of using battery to battery chargers to overcome split charging problems caused by smart alternators on modern Euro 5 & 6 vehicles.

www.12voltplanet.co.uk

 

[GRW]

As I have a van with dumb alternator - I just use an ordinary SCR (£20 ebay job). If on EHU I have a 5A DSE SMPS charger.

I believe the Lithium stuff with onboard BMS electronics etc are a lot more fussy though - so I prefer to keep it simple.
Lpg for big loads (cooking, water heating & fridge off-grid), Kero for c/heating). This means my DC needs are low enough to stick to Lead-Acid.

 

[Gareth J]

I used a split charging relay on a van conversion for AGM batteries. Think it may have been this type;

0-727-33 DURITE SPLIT CHARGE RELAY 12V 140A 140 AMP VOLTAGE SENSITIVE - CAMPERS 789545554208 | eBay UK

Find many great new & used options and get the best deals for 0-727-33 DURITE SPLIT CHARGE RELAY 12V 140A 140 AMP VOLTAGE SENSITIVE - CAMPERS at the best online prices at eBay UK! Free delivery for many products!

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Batteries were second hand when I put them in, lasted for a couple years with us and sold it to a friend who's still using it a couple of years later.

They might not be perfect but seems to work ok.