Pitfalls of Smart Chargers
I noticed a strange phenomenon over the past few weeks using my new 1.3 Amp smart charger to keep my car battery topped up.
Sometimes it wasn't topping up my AGM auxiliary battery in the rear of the car via its DC to DC charger. Sometimes it was, sometimes not.
It took me a while to figure out what the problem was but it was all to do with voltages - thank goodness I keep the manuals that come with appliances (or at least the specification sheets in the back).
The DC to DC charger turns itself on and starts charging the AGM Aux battery when the Alternator output reaches 13.4V and turns itself off when the voltage drops to 12.9v so it doesn't run down the car battery when it is not being charged.
The problem was that my smart charger floats the main battery at 13.3v.
What was happening was that if I connected the smart charger a short time after (but not immediately after using the car) it saw that the battery was fully charged so it went straight into float mode at 13.3v which was not quite high enough voltage to trigger the DC to DC charger to turn on.
However if I connected the smart charger immediately I stopped the engine or after several days of being stationary then the DC - DC charger turned itself on.
In the first case the DC-DC Charger was still charging from being driven because the battery voltage hadn't dropped to 12.9v. In the second case the smart charger did a boost charge at 14.4v first because the car battery might be slightly below its fully charged state thus turning on the DC-DC charger which will then not turn off because the battery voltage never drops below 13.3v!
Once you know what is wrong it is easy to correct. If the DC - DC charger doesn't turn on I just connect my non smart antique 4 amp charger for a few seconds which bungs up the battery voltage. As soon as the DC-DC charger turns on I can disconnect it (takes literally seconds) and leave the smart charger running knowing that it will keep both the car battery and the aux battery topped up no matter how long the car sits idle.
It took me a while to work out what was going on but the spec sheets with the different chargers solved the problem for me.
Ha ha, I bet you are fascinated by that eh?