The key to any battery charger is the basic operation. When a charging source is operating, it will supply all of the DC loads first and then what is left over will charge the batteries. For example, if you have a load running in the caravan at 10amps, say fridge and a few LED lights and you have a 20amp battery charger installed, 10amps from the charger will supply the load first and the remaining 10amps will charge the battery.
30+ years ago when battery chargers where a single stage static voltage charger, they would charge the battery and switch off. Based on this type of charger, the charger to battery ratio was 10%. With 3 stage temperature compensated “smart chargers” these days, the basic ratio of charger to battery size is now on average 15-25% of the battery capacity. So, let’s take the happy medium 20%. So, for a 100Ah battery, you would select a 20A charger.
Let’s look at charger to battery ratio for lead acid batteries below
- 100Ah Battery Capacity = 20Amp Charger
- 200Ah Battery Capacity = 40Amp Charger
- 300Ah Battery Capacity = 60Amp Charger
A lot of chargers have the ability to dial down the current output of the charger like the Enerdrive ePOWER range. Both the AC & DC2DC chargers in this range have adjustable current outputs. This allows for installing a bigger charger at the start if you think you may increase your battery capacity at a later date. This way you don’t need to buy another charger and waste money.
Now, most RV’s have multiple charging sources, mains/solar/vehicle charging. If you have the ability to run multiple charge sources at that same time, then these should not exceed 30% of the battery capacity combined for Lead Acid/AGM and 60% for Lithium.
Ultimately, you should contact your battery manufacture and discuss the best charge current required for your specific battery bank for the best overall performance and lifespan.
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