Cable Connections: Battery Bank

Raj174 · April 2017

This is the kind of situation where the need for breakers between the inverter and batteries and the controller and the batteries would be very helpful. I would diagnose by shutting everything down and and then bring the Kid online with the PV breaker off. Once the Kid is up and running switch the PV breaker on. If the battery is charging ok, then turn the inverter on with no load (load breaker off), if all is ok switch load breaker on. This might help locate the problem.

Rick

TexasOffGrid · April 2017

Rick, I did as you suggested and the system seems to have settled. Batteries are charging and the AMPs are not spiking. I'm letting the system run today full up to see how it works....both freezers pulling from the inverter as required. Will keep you posted. Thank you to all.

TexasOffGrid · April 2017

Update: Everything seems to working great. The MIdnight Kid CC allowed me to program the specific parameters for my batteries: Charge V, Float V, Equalize V. The original problem with my Chinese made CC seem to have disappeared with this US Made wonder. Thank you for all the inputs and comments....solar grids and battery banks continues to be a learning process...you guys have added to that knowledge!

TexasOffGrid · June 2017

Help. Two months with the Midnight Kid controller...which seemed to work well until yesterday. The 30AMP fuse between the Charge Controller and battery was getting REAL HOT...and failed. After replacing it, I noticed the Kid going into ABSORB mode mid-day, with the 12V batteries pretty much depleted (11.9V) each. Can't figure out why? Could the inverter be pulling too many amps from the charge controller? Appreciate any guidance here....system diagram attached.

Image: https://us.v-cdn.net/6024911/uploads/editor/ub/e06f7thvilj1.jpg

BB. · June 2017

What is the average load and hours per day are you running the inverter?

Fuses running hot/failing is not that unusual... Poor electrical connections can do it. Using automotive fuses and fuse holders can also do it (they are not really designed to run high current for hours at a time and can overheat too).

-Bill

littleharbor2 · June 2017

If your batteries are depleated in the middle of the day you are either using way more than you are producing, or have a problem in the system. Anything change in your system, or power usage recently?

Estragon · June 2017

Did you flip the pv breaker off before replacing the fuse, then let the kid boot up with battery power alone before turning the pv breaker back on?

What are the "rebulk" and absorb voltages set to on the kid?

What size of inverter do you have?

What loads were running at the time?

The battery wiring diagram looks like 3 strings of 24v in parallel for ~450ah at 24v?

westbranch · June 2017

If the setup is as shown, 800W, you have ~ 33.34A at MPPT, to cover other eventualities (like edge of Cloud events, cold days, etc) it would be wise to have a 35A or 40A fuse.
Otherwise as said, did you shut down the PV before disconnecting and restarting the KID? Always Battery first when reconnecting..!
Have you retorqued all connections? This is a common issue.

TexasOffGrid · June 2017

The input and Battery fuses on the Kid Controller are 40AMP....so I switched my 30A fuse between the controller and battery to 40AMPs...same result with overheating and the Kid failed. To answer Estragon:
The Rebulk and absorb voltages were set to battery specs. I have a 3000 Watt GoPower inverter, and run two freezers on it. The freezers are rated at 5 and 7 amps respectively. Yes, 3 strings of 24V.
Midnight Solar is sending me a new controller...and I am going to buy an automotive quality fuse to the batteries.
Thank you for the inputs.

mcgivor · June 2017

Going to buy an automotive quality fuse?? What fuse are you currently using? Automotive fuses are not designed to carry currents close to their rating for long periods, as pointed out by @BB..... just curious

Solray · June 2017

Horsefly said:

This one is also a good one, and has a "Max" feature that managed to capture the inrush current for our well pump. That feature is really handy, and not common in cheap clamp meters.

https://www.amazon.com/gp/product/B019CY4FB4

Here's another with a 'max' hold setting: https://www.amazon.com/dp/B01EX3JPY6?psc=1

Estragon · July 2017

> @TexasOffGrid said:
> The input and Battery fuses on the Kid Controller are 40AMP....so I switched my 30A fuse between the controller and battery to 40AMPs...same result with overheating and the Kid failed. To answer Estragon:
> The Rebulk and absorb voltages were set to battery specs. I have a 3000 Watt GoPower inverter, and run two freezers on it. The freezers are rated at 5 and 7 amps respectively. Yes, 3 strings of 24V.

By "set to battery specs" I assume you means 12v specs x2 for your 24v system?

littleharbor2 · July 2017

After rereading this topic, the only reference I see to your array is a stock photo showing 6 100 watt solar panels. Is this in fact what you have?

Solray · July 2017

It's a picture of his array.

He also listed the specs of it. He also included a diagram of his system after the array. The information is all there if you look.

littleharbor2 · July 2017

Solray said:

It's a picture of his array. He also listed the specs of it. He also included a diagram of his system after the array. The information is all there if you look.

As I said I see stock pictures. The 8 panel pole mount Has 72 cell 24 volt modules on it. Renogy 100 watt modules aren't 72 cell. There isn't a photo of his array.

Solray, do us all a favor and let the OP answer the question I asked of him, not you.

My point being we still don't know how many 100 watt modules he has trying to power TWO freezers. He may be underpowered.

Estragon · July 2017

OP did confirm 3 strings of 155ah@12v for ~450ah@24v. ~20a of pv to charge that is pretty marginal. Running 5+7a@120v (~60a@24v) of freezer while trying to charge would be even more so.

Maybe he does have 8x24v panels. That would make for a more balanced system, but may help explain the fuse (and kid) running hot?

Solray · July 2017

littleharbor2 said:

Solray said:

It's a picture of his array. He also listed the specs of it. He also included a diagram of his system after the array. The information is all there if you look.

As I said I see stock pictures. The 8 panel pole mount Has 72 cell 24 volt modules on it. Renogy 100 watt modules aren't 72 cell. There isn't a photo of his array.

Solray, do us all a favor and let the OP answer the question I asked of him, not you.

My point being we still don't know how many 100 watt modules he has trying to power TWO freezers. He may be underpowered.

I was letting you know. I also never told the OP not to answer you, so that is still an option and has nothing to do with my post in any way.
Thanks.

TexasOffGrid · July 2017

Hi Folks, been on business travel for two weeks overseas. Let me catch up. First, the PV picture is representative of my array, the listed specs are accurate....not the pic. Estragon asked about the Battery Specs, Yes, 12V specs X 2. I isolated the inverter from the system and have been running the NEW Replacement Kid Controller to just charge the batteries. The controller goes into Bulk MPPT just after sunrise...and the batteries are charged by 10AM (no load). The Positive cable to the batteries (past the 40AMP inline fuse) still gets too hot during bulk MPPT charging???? I am going to replace the 40 AMP fuse with a midnight solar 30AMP circuit breaker, to provide a more positive connection/protection to the system. Attaching a picture of my current fuse setup. Thank you for the inputs!

Image: https://us.v-cdn.net/6024911/uploads/editor/zj/tc9qup8qtb6w.jpg

Raj174 · July 2017

@TexasOffGrid
Could you use the new clamp on amp meter to check the positive charge controller and inverter cables, then post the results. Please do this while the fuse and cable are hot.
Thanks,
Rick

mike95490 · July 2017

If you have a cable getting hot, it is too small and cannot continue to safely carry as much current as you put through it.
If you have a 40A protection device, you need 8ga wire
If you have a 30A protection device, you need 10ga wire (and it will take longer to charge)

here's a chart for safety
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

24V 20A array = 480 watts @ 14V = 34A into batteries or 37A @ 13V

softdown · July 2017

I keep thinking freezers in Texas during the summer are possibly related to these problems. How hot are the rooms where they are located?

Your charge controller, inverter, and batteries will all last much longer if you can figure out a way to keep them "cool". Heat kills electronics. For that matter, you can look at heat as generally "speeding up the metabolism" of most things. Thus shortening the life of food, batteries, chemicals, electronics and other things.

You may have low humidity which, of course, helps with storage longevity issues.

Solray · July 2017

How hot is too hot? What temperatures are you seeing on the wire? How high is that above the room temperature? An increase in temperature may indicate too much amperage in the wire for its size.Are all of your connections properly torqued and what did you use to torque them? Is your torque wrench properly calibrated? Can you increase the voltage to lower the amperage of the system? That means using 48 volts and buying new controller and inverter.
Your other options are to reduce the draw on the circuit. Or increase the diameter of the wire. Or decrease the length of the wire.

jonr · July 2017

Not clear what wire you are using, but ~35A through 4mm wire is marginal - I'd use thicker wire or set the Kid amps down to 25A.

Then, if you have a fuse, connector or cable end getting too hot even though it is big enough for your load, it's a connection problem. It's easy to measure voltage drops at each point in the system.

myocardia · July 2017

softdown said:

I keep thinking freezers in Texas during the summer are possibly related to these problems. How hot are the rooms where they are located?

Haha, indeed! As we all know, Texas is a tiny little state.

If we use as an example one of the places I've lived, Lewisville, it was 101ºF there on the 21st, 22nd, and 23rd of this of this month, and right around 100º for the few days before and after. If someone in or around Lewisville were completely off grid, and attempting to use two freezers in an un-air-conditioned room(s), that would require quite a large amount of panels, batteries, and inverter wouldn't it? Here is the July 2017 temp. averages for there, for anyone interested:
https://weather.com/weather/monthly/l/75057:4:US

mike95490 · July 2017

Isn't everything SUPPOSED to be big in Texas ? Big Freezers. Big Solar Arrays

softdown · July 2017

mike95490 said:

Isn't everything SUPPOSED to be big in Texas ? Big Freezers. Big Solar Arrays

I'll not forget the time I celebrated two birthdays while crossing Texas.

Houston is hot and humid. West Texas is hot and dry. El Paso and San Antonio are slightly more than hot.

You really have to live there to understand Texas pride.

TexasOffGrid · August 2017

All, reference my last diagram of the solar setup. I replaced the 40A "fuse" with a Midnight Solar 30A Circuit Breaker. The wire heating seems to have fixed itself and everything is working well. The Midnight "Kid" charge controller gets fairly hot to the touch when in the full MPPT charge mode...but I assume that is normal? I appreciate all the recommendations and inputs. I'll keep you posted!

BB. · August 2017

The charge controller(s) need good ventilation... Do not install them in a closet/closed space. Keeping electronics (and batteries) cool is always helpful to ensure good life (and reducing thermal cycling is a big help too).

-Bill

Estragon · August 2017

Inside my classics run about 50°C, and they're fan cooled. IIRC, the Kid is sealed with no fan, so would rely on heat sinking to cool, which I expect would get pretty warm.

TexasOffGrid · August 2017

Great points. Thank you!

Cable Connections: Battery Bank

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