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How bad is it to Overcharge Caravan Batteries?

Can overcharging a fully charged caravan battery cause damage it?

Question: I am currently charging my caravan battery (130Ah AGM) from the tow vehicle (2015 Colorado7) via an Anderson plug and voltage sensitive relay. My question is, can this cause damage to the caravan battery through overcharging a fully charged battery as there is no management of the power input?  Would I be better of running this through a DC-DC charger and if so, is this better placed within the car or in the caravan? (from Ken Saxby)

Answer: Advisable to make sure that your setup is not going to cause problems with overcharging of your 12 Volt battery in your caravan. An Anderson plug and voltage sensitive relay should be able to provide a basic level of charge for your caravan, however it won’t be as good as the installation of a proper DC-DC converter.

Probably the first thing to check would be to understand whether your vehicle has a smart alternator, as you will need to set up a system that can cater for either option. The best way to detect if your vehicle comes equipped with a smart alternator is to visually check if there is a small box on the side of your battery closely connected to the negative terminal. This device senses information and feeds it back to the ECU in the car enabling the vehicle to reach required emission controls by having the alternator output reduced when not required for standard operation of the vehicle. 

If your vehicle's fitted with a smart alternator, then you will need to definitely run a DC to DC charger.  The DC-DC charger is able to boost up the lower voltage when the alternator goes into reduced capacity output as otherwise the minimum voltage required on the VSR will not be reached and not operate preventing any voltage or charge to your caravan battery. In the alternative that there is no smart alternator in your Colorado then a VSR setup will provide you with basic charge requirements.

Secondly, it would be good to understand your caravan’s power management system.  Many systems out there actually have a built in DC-DC module that enables the caravan to be charged by not only AC, but from your vehicle and solar.  In this case, you should feel very comfortable that there is no chance of overcharge to battery and it will be properly monitored with overvoltage protection.

In the absence of a power management setup, it is unlikely that with either setup your battery would overcharge your caravan. With your the current setup of a voltage sensitive relay, this should cut off if the voltage is to get too high as many of the units on the market cut off at approximately 13.5 volts. While it is not healthy for a battery to have a constant excessively high voltage connected to the terminals the main problem is that the battery is not be charged through a multi-stage charger which would normally have at least the basic charge stages of absorption, bulk and float charge.  These modes, which can be up to 7–9 different stages depending upon the charger, charge a deep cycle battery properly according to specific voltage and charge requirements which provide a healthier and longer lasting battery.

Another advantage of installing a true DC to DC charger is that firstly, they can charge a wide variety of batteries and secondly, most reliable units available can also take charge through solar panels as well, therefore making the product multi-functional. For example, you could add portable solar panels to follow the sun to recharge your batteries during the day if there was shading over the top of your caravan preventing charge from the rooftop panels.

If you determine that your setup requires a DC-DC charger, it is more advisable to install in the caravan rather than the car and as close as practical to your battery including fusing.

In short Ken, your current setup is unlikely have issues with over charging your caravan battery but also won’t provide optimal charge to your battery either but may be sufficient for your needs.  Hopefully this assists in answering your question and also providing some more background.

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