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Mod #8: Converter Upgrade

Posted By Mark Corgan On June 12, 2008 @ 6:19 am In electrical | 5 Comments

RVs have sophisticated electrical systems. Where else can you find a 120 VAC system AND a 12 VDC system all in a package that doubles as a power distribution center and a battery charger? This package is referred to as a power center and it serves several purposes. One purpose is to convert the AC power supplied by shore or generator power in to DC power to power things like lights and the water pump. Another is to provide AC power to things like the microwave and the air conditioner. And although the converter is also a battery charger, most RVs come with cheap converters that make for very poor battery chargers. This mod will get you on the path to battery charging nirvana.

Mod Difficulty:

One converter brand often found in RVs from the factory is the Magnetek 7300 series, a decent power distribution center but it only has a single stage battery charger. This means that the charger provides a constant DC voltage all the time, no matter what the demands placed on the DC system and the battery. This might be fine for lighting but makes for very long battery charging cycles. The voltage and current supplied to the battery for charging must be such that it optimizes the time taken to charge the battery and at the same time does not damage it by overcharging. This is where a 3-stage charger comes in to play.

A 3-stage 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.

Upgrading the converter section of a Magnetek 7300 series power center with a 3-stage charger is a very common mod. Most choose the Intellipower PD9100/9200 series charger since it is pretty easy to install. The PD also has the provision for a smart controller called the Charge Wizard. This allows manual control of the stages the charger uses with a pendant that plugs in to the charger. Sometimes it’s necessary to force the charger in to a mode other than what it chooses automatically.

If the power center is fairly old, some opt to replace the entire power center with one of the more modern ones like the WFCO brand, which comes with a 3-stage charger built in. This makes for a cleaner all-in-one installation but requires swapping out both the AC and DC wiring to the unit, whereas just swapping the converter section with the 3-stage PD charger involves as few as 5 wires. Rather than detail the actual converter upgrade here, I will instead provide you with links to a few excellent sources by fellow RVers that documents the whole kit and caboodle.

TipTo get the most battery charging benefit from your new converter charger upgrade, be sure to look at the existing DC wiring to ensure the proper gauge charging wire. If you are upgrading to a higher current charger, the charging wire to the battery should be sized for the maximum current output of the charger.

ModMyRV recommends these parts for this mod:

Converter Chargers
Inteli-Power 9200 Series Converter/Charger, 60 Amp
Parallax Power Components 7345 Converter/Charger
Tripp Lite PowerVerter RV Inverter/Charger RV2012OEM - power converter + battery charger - 2 kW

Converter Charger Upgrades by Fellow RVers
Magnetek Converter Upgrade to Intellipower PD9160
Parallax Converter Upgrade to WFCO Converter Charger

Wire Gauge Sizing Chart
AWG Wire Size Chart and Voltage Drop Calculator
AWG Wire Size and Length Chart

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