[C320-list] Xantrex DC Controller - functions?

[Jack Brennan]

Hi David:

The Xantrex is the controller for the solar panels. By the way, I believe it is a PWM controller, which is not nearly as efficient as the MPPT controllers. The price on MPPTs has become more reasonable, and it’s probably worthwhile looking at a new one that also has an LED showing battery charge info rather than just blinking lights.

A couple of thoughts:

• The 13.1 reading is probably coming as the solar panels are charging your house bank. That means the real state of charge is not 13.1, but more likely 12.3 or so. Try disconnecting the solar panels and letting the batteries sit for an hour with no load on them before checking the voltage.
• A 400-amp house bank takes a lot of charging to bring it up to full. You don’t say how large your solar panels are, but even a couple of 160-watt panels would take more than 10 hours in perfect conditions (and with an MPPT controller) to bring the batteries from half full to near full.
• Your diesel probably has a stock alternator originally designed for a car. This means it’s good at charging your batteries to about 80 percent, but the rate of charge drops sharply after that. I’ve read it can take 8 or 10 hours to fully charge a battery bank with the alternator.
• You are only getting a partial charge from the PWM controller when the batteries are above 80 percent because it is not very efficient. So even on a sunny day, it will be slow going for the solar panels to top off the batteries.

My guess is that your batteries are being somewhat undercharged, which can damage them in the long run. The Xantrex is probably giving you the correct information, but you’re not getting enough data to understand the situation because you don’t have an LED on it.

My recommendation would be to buy an MPPT controller (you can get a Renogy 20 amp for $100), install it and see what the LED screen tells you. 

For some perspective, I have two 160-watt solar panels with an MPPT controller charging four golf cart batteries rated at 400 amps. I run the fridge 24/7, and it takes until about 1 p.m. in sunny Florida to bring the bank up to float stage at the dock with no other electric usage.

The panels put out close to 20 amps on a sunny day with the MPPT, but that goes into the batteries only when they are partly drained. The rate of charge drops to 4 or 5 amps as the batteries get close to full. It will be less than that with the PWM.

Good luck. Hope this helps.

Jack Brennan
Sonas, 1998 Catalina 320
Tierra Verde, Fl.
Dolphin Cruising Club of Tampa Bay







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From: David Hayes
Sent: Sunday, October 18, 2020 4:55 AM
To: c320-list at lists.catalina320.com
Subject: [C320-list] Xantrex DC Controller - functions?

H