Solar panel wire- positive wire hot to touch

[miataroadster]

I have added an mc4 connectors and attached T-branch splitter connectors to the end of wires before mppt charger. I did that to split the power between mppt and a solar powerstation and for easy connect/disconnect. Most of the times my coach LiFePO4 batteries are fully charged, and so I thought it will be more useful if I redirect the unused solar power to my powerstation(solar generator).

It has been almost three months since the installation and all is working fine.Coach batteries and/or solar generator being charged. Today, I was tinkering with the wiring and I noticed that the end of positive wire coming down from the roof is hot to touch, and so as the MC4 and T-branch connector. I measured the current output as high as 25 amps, hovering 19- 22, over cast. I was surprised of that being all panels are flat on roof! I have total of up to useable 600 watts.

I used to have only one 200 watt solar panel and added two addl 200 watt panels and used the same 10 awg and gopower 30amp mppt.

Per the attached picture, A is the T-branch and B is the end of wire with MC4. Spots A and B are hot to touch like holding a fresh coffee out of a paper cup hot. Is that normal? I wish I have a temperature gun so I can really tell the exact temp.

 

[Heavy Half Ton]

I had a three into one mc4 connector go bad. Really confused me, as it was so simple. I gut it apart and found one leg was never screwed into the base, it was just touching the threaded shaft it was supposed to be attached to. Same deal. Hot= bad connection.

 

[miataroadster]

Ah. You just gave me an idea, thanks! I will swap the two splitters to test if positive still heats up.

 

[PhilFromMaine]

10 gauge wire is only good for about 25-30 amps. A full 600 amps could generate as much as 47 amps. IMO, you should expect hot wires even though you aren't pulling the full wattage through the wire. You never had the problem before because you only had one MPPT and battery pulling amps from the 10 gauge wire. The MPPTs are sort of the gate keeper for what is being pulled through the wire. With mostly always charged batteries, that would not be a lot of amperage, but with a sunny day and two discharged batteries, the amperage would be substantially higher.

 

[Aussieguy]

MC4 not the greatest connections
good for easy install but not the greatest at letting power through

If the joint is HOT ... look at eliminating IT
Only reason to have connector is for maintenance
if you don't intend to pull panels up and change the wiring a lot ........... look at splicing the cables

maintenance may take 5-10 minutes longer if you have to cut off a splice and replace it
but worth the effort for a hobbyist / user who will probably only do this once every 10years
just make sure you got good crimps and crimper some good heat shrink

leave plenty of wire from panel so you can cut off/replace crimps if needed.

wire between panels too short... can be replaced with good solder skills

 

[GolfingDave]

A full 600 amps could generate as much as 47 amps.

Typo? Watts?

Question though, wouldn't the Solar Generator limit the amps during charging? OP does not say what unit he has or the current limit it charges at.

I measured the current output as high as 25 amps, hovering 19- 22

Seen that or at least 23 on my Solar Controller and they are flat on the roof, 600 watts.

 

[miataroadster]

10 gauge wire is only good for about 25-30 amps. A full 600 amps could generate as much as 47 amps. IMO, you should expect hot wires even though you aren't pulling the full wattage through the wire. You never had the problem before because you only had one MPPT and battery pulling amps from the 10 gauge wire. The MPPTs are sort of the gate keeper for what is being pulled through the wire. With mostly always charged batteries, that would not be a lot of amperage, but with a sunny day and two discharged batteries, the amperage would be substantially higher.

Wow, that's a lot of amps for 600 watter!

I guess you're right about two MPPTs of the power station and extra battery for it. There was a significant amperage flowing to charge those each 2048Wh at 50% remaining power capacity. But still, wire should be warm and not hot...

So I checked the wire, but could not separate the (+) MC4 connections. Pin stuck inside, I assume plastic got so hot it melted the inside. The outside looked normal.

I cut the wire and replaced it with a new Y-splitters. So far so good. I will keep an eye on it.

 

[miataroadster]

MC4 not the greatest connections
good for easy install but not the greatest at letting power through

If the joint is HOT ... look at eliminating IT
Only reason to have connector is for maintenance
if you don't intend to pull panels up and change the wiring a lot ........... look at splicing the cables

maintenance may take 5-10 minutes longer if you have to cut off a splice and replace it
but worth the effort for a hobbyist / user who will probably only do this once every 10years
just make sure you got good crimps and crimper some good heat shrink

leave plenty of wire from panel so you can cut off/replace crimps if needed.

wire between panels too short... can be replaced with good solder skills

I'm hoping it was user error...like I did not crimp pin correctly or didn't push the connectors together right.

I used the stock wire. I assume it's a 10 awg. Outer diameter of wire is about 2.9mm per my cheapo caliper. Is it the right size?

For now the MC4 is for convenience, for easy charging of the powerstation when house batteries are charged. I might eliminate the Y- splitter to lessen MC4s like you suggested.

 

[miataroadster]

Typo? Watts?

Question though, wouldn't the Solar Generator limit the amps during charging? OP does not say what unit he has or the current limit it charges at.


Seen that or at least 23 on my Solar Controller and they are flat on the roof, 600 watts.

Yes, the MPPT limits incoming amperage. The Oupes Mega2 powerstation input amp limit is 15a. The B2 smart battery for it is also 15a. I use the splitter and can see that the amperage coming from solar array is distributed (not evenly but close) to each unit.

I was surprised that I read that high of amps when it was a bit cloudy yesterday! I can't wait to see what I'll get this summer, and utilize the adjustable brackets to maximize sun exposure.

 

[GolfingDave]

Yes, the MPPT limits incoming amperage. The Oupes Mega2 powerstation input amp limit is 15a. The B2 smart battery for it is also 15a.

For some reason I was thinking your panels were charging one or the other, I think it was when I read "easy connect/disconnect. So you could possibly go over 30 amps with the 10 gauge wire. Serious problem? I doubt it or they would not build current curves into circuit breakers. Let both devices discharge a bit and check the current on a sunny day if curious.

They do make a fuse holder that looks like an MC4 connector. If concerned about it you could put one after the panels on the roof. I have one at my roof connection point. It would protect the wires you can not see down to the splitter that is going to carry the most current. It sounds to me the splitter is inside?

 

[miataroadster]

Let both devices discharge a bit and check the current on a sunny day if curious.

They do make a fuse holder that looks like an MC4 connector. If concerned about it you could put one after the panels on the roof. I have one at my roof connection point. It would protect the wires you can not see down to the splitter that is going to carry the most current. It sounds to me the splitter is inside?

Yes, I put one or two of those 30a inline MC4 fuses at the roof splitters. I know I have a spare somewhere.

Yes, the two other splitters are located inside before the rv mppt charger. I'll put a 30a fuse there(+).

It is going to be partly cloudy today, but Ill test. Yeah, I noticed that I was reading only 14amps pull yesterday. So you're right, the Oupes devices were almost fully charged. I'll discharge both Oupes units down to 20 percent to possibly max amp pull from panels.

 

[hamrover]

Uhhh. Sorry for this. I didn't mean for it to be so long before I started typing.... But if we are knocking on the door of 30A here for only 600W panels - this might be worth some consideration:

The max amps that your pre-MPPT wires (10 AWG in your case) and connectors can expect to see is also a function of several things besides straight Watts. It might be worth examining the solar panel ratings and configurations to keep amps down to safe levels.

Panel Rated Operating Voltage:
The first thing to know is the rated operating voltage of your panels (for later math). Let's say they are 20V panels.

Arrangement:
For the total of 600W panels: Are they 6 x 100W arranged in (3s X 2p), or 3 x 200W arranged as 3s, or 2 x 300W configured as 2p, or some other configuration?

Math:
If they are the first config (20V, and 6 x 100W in 3s x 2p) - then each parallel circuit of 3 panels in series will at max be producing 60V * 5A for 300W, and then when they add together to reach 600W at your main junction point, you would be seeing at most 60V * 10A for your 600W. So this sample configuration should not see more than 10A.

Following the same math, the second sample config with maybe a 19V base panel would yield 57V * 10.42A at the main junction point.

In the third example, let's assume an 18.2V base panel. Arranged as two panels in parallel - which would give us 18.2V and 32.9A! max at the junction point and beyond, all the way to the charge controller!

The main takeaway is that careful panel arrangement and using higher voltage panels and series configurations to your advantage will keep your amps down in your wires PRE-Charge Controller. (Be sure to check charge controller voltage input limits). In that 3rd example above, simply reconfiguring the panels in series (as long as your charge controller can handle 37V), then your amps cut in half down to 17A - much more manageable.

I only bring all this up - because your 600W panels are reading 25A sometimes - and if you are in this third configuration, and not yet up to peak production, it might be worth reconsidering some other things.

After the charge controller is a different story all over again because now you are down in the 13-14V range.

Wire:
The final check would be to determine the temperature rating of the insulation of your 10 AWG wire, since this will determine actual amperage rating, and all wires are not created equal - unfortunately.
Here is a table with a few common wire temperature ratings (most decent wires I have encountered seem to be 105℃). The fact that it is getting warm to the touch is worrying.

Lasly, the MC4 connector:
Most MC4 connectors, if not specifically stated, are only rated to 30A. Cheap alternatives and/or failed units might not reach this number (as noted and observed by others in the thread). I hope it is only a failed connector for you at this point, but also worth considering if it failed in the first place due to potential overloading beyond 30A, or some other arbitrary rating.....

Good luck!

 

[miataroadster]

I have 3 x 200w panels in parallel. 23v VoC, 19.2v OoV, 10.42a OoC, 11.05a ScC.

The Oupes devices each accepts 12-150v, 1200 watts, 15amps.

I spent about 4 hours today observing the surface heat of wires and connectors. However, the highest I saw was only 21amps vs 24 the other day. Surface of new connectors as warm as 70 deg F per my cheapo temp gun.

The other day, old connectors was so hot I could not hold it for longer than 10 seconds!
So after replacing them, it looks like I'm within the specs per the table above and conclude that it was a defective T splitter.

Another observance today- the power station and gopower mppt is working fine with split charging. However, it's different with the power station and extra smart battery charging. Their own mppt is (fighting) each other pulling amperage from the same solar array! I saw the fluctuations of wattage input on each unit. Either I charge the power station and it's battery as one unit or charge one with the rv solar array and charge the other with a separate(portable) solar panel/s.

 

[ppine]

Check connections. You need to run a new cable to handle the load from 600 watts. It is not safe.
600 w divided by 12 v is 50 amps. Your wire is under sized by a lot which is why it is hot. Check the table. You probably need 6 gauge. Do it soon before you burn it up.

Your controller is also under sized and needs to be replaced. I use a 40 amp controller for 400 watts of solar.

 

[hamrover]

I have 3 x 200w panels in parallel. 23v VoC, 19.2v OoV, 10.42a OoC, 11.05a ScC.

I want to make sure we have a good picture of what you have going on here.

I am imagining your setup looks somewhat like this, if your 3 x 200W panels are wired in parallel (I put MC, but meant to put MC4 to show where your connectors and 10AWG wire are):

I am not sure what your split charging setup looks like, or how that is wired. Is all that after your charge controller (below it in this pic), or before your charge controller (above it in this pic)?

 

[hamrover]

Actually, a few quick amendments - If your charge controller is the GoPower 30 MPPT (I could only find specs for one online) then it looks to be able to accept your setup of 300W x 2 panels (600W) in either config (series or parallel) - so the remaining concern is that right at 30A you are at max capacity for the MC4 connectors, and perhaps slightly beyond. With a 30A inline MC4 fuse, you may occasionally blow the fuse.

Your charge controller will only put out 30A to the batteries ("Rated Current Charge = 30A"), but with 600W on the input side you are right at the capacity of the controller again (and even slightly beyond), so it is likely to see that full 30A much of the time - so best to check those wires for ratings vs the chart above as well. I would expect temps are going to be warm in your current setup, even at the charge controller, and it doesn't leave much headroom for heat dissipation or slight over current conditions. Probably good to make sure those going to the battery are high quality 10AWG or better.

It looks like your charge controller might be leaving a little bit on the table in terms of not being able to pass through your full 600W capacity with that 30A output rating - so if you ever did decide to upgrade it - you would need to re-evaluate the increase in amperage that would result on your wires running to the battery and for sure look at 8 AWG or 6 AWG.

I'm still curious what your split charging looks like - are you using the "dual battery charging" of your solar charge controller to accomplish this?

 

[Aussieguy]

Check connections. You need to run a new cable to handle the load from 600 watts. It is not safe.
600 w divided by 12 v is 50 amps. Your wire is under sized by a lot which is why it is hot. Check the table. You probably need 6 gauge. Do it soon before you burn it up.

Your controller is also under sized and needs to be replaced. I use a 40 amp controller for 400 watts of solar.

10g panel wire can handle more than 600w as long as you increase the voltage
12v panels do NOT produce 12v ... they usually produce around 20v
24v panels produce around 33 - 37v

then you can put the panels in series to increase the voltage even more
20v x 3 (3 panels in series) = 60v x 10amp = 600w
MORE voltage = less amps for the same total Watts

Wire size from ROOF to CONTROLLER 10g will work adjust your voltage /amps by series & parallel
----------------------------------------------------------------------
Controller to battery
YOU can't really increase the battery charge voltage from the controller
and you have a max amps the controller can send to battery

14.2v x 30amp = 420w
so the 30amp controller is only good for around 420w
Wire SIZE for battery to controller must be worked out based on the distance to the battery and the volts & amps (use a calculator)
-------------------------------------------------------------------
Over paneling............ NOT a good IDEA if you live in the south and get good solar numbers

most people will use 600w on a 30amp mppt controller because the vast majority of the day ... flat panels won't be producing the MAX wattage .... around noon the panels will produce close to the 600 watts ... the MPPT will just dump any excess amps

 

[GolfingDave]

Can someone explain about all this amperage?
Go Power says this and this is the fuse I installed. I figure the manufacturer knows something when they say the fuse will likely never blow.

Edit: Looks like @Aussieguy responded while I was typing.

 

[Aussieguy]

slow typer ... sorry


EDIT.... my 10g pre-wired install is carrying
37v x 20amps = 740w

 

[GolfingDave]

slow typer ... sorry

Clairvoyant is how I took it, almost like Carnac The Magnificent.