Confused with mt50

micahmicahok · December 2019

Hey everyone! I have a solar kit from renogy hooked up into my camper van. Ive got 2x100w solar panels, 40a mppt charge controller, 200ah agm battery, and the mt50 meter. Sometimes I’m worried my panels aren’t putting in enough power like they should be but don’t know how to troubleshoot. My mt50 meter is like this right now with 2 small led lights on, max air fan on, and my dometic 65w cfx fridge on for about an hour today. It is slightly overcast today as well. Any help would be greatly appreciated.

Estragon · December 2019

With clouds (or any shade) you may not get much from the panels, making it harder to troubleshoot.

Working properly, I'd guess with the mppt in bulk charging mode and the battery discharged to under 80% full or so, you should see PV voltage of roughly 18v, and current of maybe 10-12a into the battery. As the battery gets over 80-85% full, the battery voltage should be held at about 14.4v and current into the battery should slowly (couple hours) drop off to around 2-3 amps. After fully charged, the controller should hold the battery at a float voltage of something like 13.2v or so as long as there's enough sun to hold it there.

Any shade, even a small vent pipe, bare tree branch, antenna, etc close to a panel could reduce the output to near nothing.

littleharbor2 · December 2019

Try aiming the panels at the sun. The sun is at it's lowest point in the sky this month Dec. 21 is the lowest, and the start of winter. I presume your panels are either laying flat or shaded with the low current output shown.

micahmicahok · December 2019

littleharbor2 said:

Try aiming the panels at the sun. The sun is at it's lowest point in the sky this month Dec. 21 is the lowest, and the start of winter. I presume your panels are either laying flat or shaded with the low current output shown.

They’re flat on my roof so I can’t really aim them differently and nothing was shading them.

micahmicahok · December 2019

Estragon said:

With clouds (or any shade) you may not get much from the panels, making it harder to troubleshoot.

Working properly, I'd guess with the mppt in bulk charging mode and the battery discharged to under 80% full or so, you should see PV voltage of roughly 18v, and current of maybe 10-12a into the battery. As the battery gets over 80-85% full, the battery voltage should be held at about 14.4v and current into the battery should slowly (couple hours) drop off to around 2-3 amps. After fully charged, the controller should hold the battery at a float voltage of something like 13.2v or so as long as there's enough sun to hold it there.

Any shade, even a small vent pipe, bare tree branch, antenna, etc close to a panel could reduce the output to near nothing.

I don’t know how to tell if my battery is drained below 80%. I see the battery symbol at well below half but It was completely full before I turned on the lights/fan/fridge. Only having them on for an hour or so I can’t imagine that battery symbol is accurate.

Estragon · December 2019

One thing you might try is tightening/checking the PV input wires. I'm assuming this is a new installation, and screw-down connections can loosen a surprising amount from a tight initial connection.

micahmicahok · December 2019

Estragon said:

One thing you might try is tightening/checking the PV input wires. I'm assuming this is a new installation, and screw-down connections can loosen a surprising amount from a tight initial connection.

Are you saying where they connect into the charge controller?

Estragon · December 2019

Yes, and anywhere else they connect with a screw-down type connector. What happens is the copper wire cold flows around the bolt under the initial tightening pressure in the first several hours. I snug this type of connection up after the first day or so, and am surprised at how loose they can get in the meantime.

MC4 connectors, like what your panels likely have, don't do this. They can be damaged by making/breaking connections with current flowing though, so I always turn off the controller and cover panel(s) when connecting/disconnecting.

micahmicahok · December 2019

Estragon said:

Yes, and anywhere else they connect with a screw-down type connector. What happens is the copper wire cold flows around the bolt under the initial tightening pressure in the first several hours. I snug this type of connection up after the first day or so, and am surprised at how loose they can get in the meantime.

MC4 connectors, like what your panels likely have, don't do this. They can be damaged by making/breaking connections with current flowing though, so I always turn off the controller and cover panel(s) when connecting/disconnecting.

Alright sounds good I’ll check that tomorrow. I just can’t tell if that 2.3w of power from the panels is right and if so is that way to little for 200w of solar

Estragon · December 2019

Roughly where are you located?

micahmicahok · December 2019

Estragon said:

Roughly where are you located?

I’m in Michigan. Much less sunlight today.

Estragon · December 2019

Using Lansing as an example, Dec only averages 1.3 "full sun equivalent" hours/day of sun on flat mounted panels. Not much you can do about it, but just for comparison panels mounted at 70° facing south would see more like 2.57hrs.

Hopefully you'll get some sunnier weather soon.

One other possible issue occured to me. In hooking everything up, could the controller have seen pv voltage before battery voltage? Sometimes a controller can get into a weird state if booted up at pv voltage. For example, it may think it should be 24v nominal bank. To avoid this, the controller should be fully booted up on battery power only.

littleharbor2 · December 2019

The low (13.6) voltage from your panels looks suspicious. You should be seeing higher voltage than that. Is there snow on the panels? Are all connections from the panels to the controller solid?

Confused with mt50

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