MX60 voltage reading more than 3V too high

Discussion about the MX60 Charge Controller

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My RE system: 10 x 80W (12V) panels. 5 pairs connected to create a 24V string
6 x 12V 200Ah AGM batteries connected in pairs to create 24V bank
MX60 charge controller
Axpert 5kW 24V inverter

MX60 voltage reading more than 3V too high

Post by BulungulaDave »


I have a MX60 that has worked very well for about a decade. It was being used on a 24V system using deep cycle 2V lead acid batteries. I recently upgraded that site to Lithium and so I didn't need the MX60 there anymore. So I decided to move it to a different site.

This new site is also 24V but uses 6 x 200Ah AGM batteries. It has 10 x 80W panels connected in 24V pairs. I use an Axpert 24V inverter (which has 3 x 220W panel connected in series to it).

However, I noticed that the MX60 is reading about 3V higher than both the Axpert and my multimeter. See photo below. This means that the Mx60 enters Float mode while the batteries are more or less empty and is messing up the whole energy system.

I have reset the MX60 to factory defaults but still no change. If I disconnected the Axpert - no change.
See photos below (Multimeter connected to Bat+ and Bat- terminals inside MX60)
Any ideas?

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Re: MX60 voltage reading more than 3V too high

Post by ralphday224 »

Beena while since I had my MX60, but there's a menu/procedure to calibrate to the battery voltage. Check your manual or missus Google for the how. Sounds like the when is now.
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Mike Curran
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My RE system: Outback - Garage roof (2007/2017):
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied VFXR3524A-01's series stacked, replaced GVFX's (2020)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS. Tigo ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 microinverters

Battery systems operate in grid-tied, net metering w/backup mode
All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: MX60 voltage reading more than 3V too high

Post by Mike Curran »

I have an MX60 (on a shelf) and the hard copy manual that came with it. The manual doesn't say but I'm doubtful you can adjust Vbatt calibration by 3 volts. I've been wrong before, though.

From the system description it sounds like the array input voltage to the MX is a bit low for a 24V battery:
10 x 80W panels connected in 24V pairs
Maybe I'm misinterpreting it, though. If not, I'd try wiring the array to get a higher input to the MX. Might not explain the voltage discrepancy but if 24V is all that's going into the MX then it's not gonna do a good job charging a 24V battery.
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