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Mod #4: Battery Charger

Posted By Mark Corgan On June 8, 2008 @ 7:12 am In electrical | 9 Comments

Battery chargers come in all shapes, sizes, and charging abilities. There are automotive chargers, trickle chargers, portable chargers, smart chargers, and dumb chargers. You name it, there is a charger made for it. Arguably, the two most popular used in modding your RV are the Vector (or Black and Decker) smart charger and the Intellipower PD9100/9200 series charger. The Vector is a portable and the the PD is a permanent mount, typically used when upgrading the charger section of your RV’s converter. These are both so-called “smart” chargers because they each offer several charging profiles that are much more friendly to your batteries than a single stage or “dumb” charger. Here is why.

Mod Difficulty:

A typical “dumb” 12-volt battery charger provides a constant voltage, usually around 13.6 volts, while the charge current is determined by the internal resistance of the battery. What this means is that when the battery is deeply discharged, it has low internal resistance and thus will draw as much current as can be supplied by the dumb charger. As the battery charges, the internal resistance increases, decreasing the current draw on the charger down to a trickle. Charging in this manner can cause several problems. The battery can get too hot and be damaged because the charge current may be too great. If the battery is not overheated during charging, leaving it on a dumb charger can boil the electrolyte out of the battery because the charging voltage is too high.

The typical “smart” charger provides a way to charge a battery in stages, which are commonly referred to as bulk (or boost), absorption, and float. The bulk stage provides a safe constant current while increasing the voltage high enough (14.2-14.4 volts) that the battery can be rapidly recharged to around 90%. At some predetermined time, or when the current draw cannot be held constant, the charger will switch to absorption mode. This mode reduces the voltage to 13.6 volts and supplies current as needed to finish the charge. At this point, the charger will switch to a float mode voltage of 13.2 volts, provided there is no demand on the battery.

So how does this help you mod your RV? Well, it really doesn’t but it will give you peace of mind at 3AM when you’re thinking about what to do when your batteries are boiling themselves dry. Simply hookup the Vector, select the current level, and go back to sleep. The Vector will do the rest for you. If you want to get fancy and not have to hookup a charger each time, then do the Intellipower charger mod.

This involves removing the converter/charger section within your AC distribution panel, and substituting the Intellipower charger. This can be done relatively easy if you have basic electrical skills. There is another mod that details how to upgrade your converter so I won’t go into detail here. But I have included some links below that should help you get a feel for what’s involved. As always, be sure to disconnect shore power, battery power, and/or solar power before attempting this mod.

ModMyRV recommends these parts for this mod:
Battery Tender 021-0123 Battery Tender Junior 12V Battery Charger
Black & Decker VEC1093D Smart Battery Charger with 110 Amp Engine Start and 40/20/10/4 Amp Rates
Amptronix 45Amp 12V Multi-stage Smart Charger with 2-Bank (ABC-1245A2)

General Reference
Wikipedia Smart Charger Reference

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