Midnite Classic 150 reads battery voltage wrong

Started by CountryFit, June 25, 2018, 01:27:08 AM

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CountryFit

Since two days ago, my Midnite Classic 150 has been always at "float", no matter what the battery voltage was at. The battery voltage on the LCD display was always the same as what the charge volt was set at (14.1v) although the battery was actually 13.3v. When I set to run on Bulk, within seconds, it would shift out of Absorb into float (because it saw that battery voltage had reached the voltage set as float).

I am not sure which chip reads the battery voltage, whether it is on the communication board or on the power board.  I am grateful if someone knows/shares the knowledge.  I might have to replace the bad board.

(The positive terminal to the battery was overheated although I was using 2ga wire.  That might be the cause).  Here are photos showing how it is looking like now.  The communication board appears intact.




Vic

Hi CountryFit,

It looks like the Positive battery connection on the Classic had a loose/poor connection. This causes some resistance.   At high current (perhaps some time ago)  any appreciable resistance will cause heating at that connection point.  This heating can damage the terminals,   causing additional resistance.

The resistance at the battery positive terminal,  with current flow,  causes a voltage drop between the Classic and the battery.   This voltage drop could cause the Classic to incorrectly measure the actual battery voltage.

The power terminals of the Classic blue connector block  are NOT designed to accept  wire larger than #4 AWG coarse-stranded cable.

Perhaps you can carefully clean and burnish the burned connector terminal/s,  and replace the cable with #4 AWG THHN type building wire.

Torque all screw type power terminals correctly,   AND re-torque them in about 24 hours.

Do NOT use fine-stranded cable with this type of screw terminal.

This is my read on things,   FWIW,    Vic

Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

CountryFit

Thanks Vic!
I discovered the overheat on the positive terminal 2 months ago. I slightly enlarged the size and inserted a 2ga wire.  For that matter I also called Midnight suggesting making those accepting 2ga wires.  But I didn't think the tech support would ever pass my request to anyone/managers (he said "we have been doing this since 1960s..." of course he wouldn't take an external engineer's opinion).

My charge current had been always in about 90a at 12v nominal in 3 seasons a year.  Even with 2ga wire, it was still super hot. I even tinned the wire into solid before plugged in and tightened it well, now I saw the wire pvc shield was charred badly.  I'll clean it well tomorrow and see if that helps.

Big thanks again!
Steve

Robin

The Classic cannot be redesigned to accept 2AWG. There just isn't room. I am surprised your large wire is running hot though. The terminals accept 4AWG. Even at 100 amps, the 4AWG wire should not be running hot.
I have always found that tinning the strands is a bad idea. Solder will cold flow and thus loosen up over time.
Do you have 2AWG running to a breaker close to the Classic? That is the norm and then a 4AWG going to the Classic which is normally only a couple feet.
Robin Gudgel

boB


The battery voltage is read by the processor on the control board.  If there is a bad connection at the terminal block, then that high resistance will show up as a higher voltage at the controller and as you saw, a lower voltage at the battery terminals.  The processor should see the voltage at the terminal block on the Classic power board though.   There is a connection through the 12 pin connectors to feed battery voltage up to the control board to power it and also measure that voltage.

A long time ago I think we saw one Classic with an unsoldered connection from the terminal block.  If that happened then that could also cause a voltage drop like this.  You could wiggle the connector or the terminal block and see if there is any difference in readings I suppose.

So, with 7 amps or so of current like I see on the MNGP display, there must be some heat dissipated.  Say, 14.1V - 13.3V = 0.8 volts and that multiplied by 7 amps is about 5 watts or so and should get pretty warm.

If you can repeat this situation, can you take your volt-meter and measure a voltage drop  between the battery plus terminal and that wire ? 

The battery negative and PV negatives are tied directly together on the power board and the positive PV input to positive battery output is where all the change in voltage happens.  But voltages are measured from minus to plus on the circuit board where the terminal blocks are soldered to.

Even though we have been doing this a long long time though doesn't mean there are still strange and new problems that crop up !  Learn something new every day !

boB

K7IQ 🌛  He/She/Me

boB

Quote from: Robin on June 25, 2018, 02:39:14 AM
The Classic cannot be redesigned to accept 2AWG. There just isn't room. I am surprised your large wire is running hot though. The terminals accept 4AWG. Even at 100 amps, the 4AWG wire should not be running hot.
I have always found that tinning the strands is a bad idea. Solder will cold flow and thus loosen up over time.
Do you have 2AWG running to a breaker close to the Classic? That is the norm and then a 4AWG going to the Classic which is normally only a couple feet.

This is all good but it sounds like there is a bad connection somewhere.  4 AWG should have very little drop at 7 amps.

And as always, thank you Vic for you valuable input !

boB
K7IQ 🌛  He/She/Me

FNG

Not much to add to what Robin and boB said, The Classic was in float because the positive battery side likely has a bad connection, I would put a call in to tech support today and Kyle or some one can help you get fixed up

CountryFit

#7
Thank you everyone!!

I am posting another photo showing how bad the positive 2AWG was.  The right hand end was to the terminal on the board.  The left hand end was to the breaker.  Obviously, it's been extremely hot.  According to your experience, this shouldn't have happened.

CountryFit

Quote from: Robin on June 25, 2018, 02:39:14 AM
Do you have 2AWG running to a breaker close to the Classic? That is the norm and then a 4AWG going to the Classic which is normally only a couple feet.
Yes I use two breakers - one is at the upstream of the controller about 7" away, another is at about 7" downstream. 

CountryFit

Quote from: boB on June 25, 2018, 02:40:03 AM

The battery voltage is read by the processor on the control board. 
Did you mean "control board" the power board or communication board?

Quote
If you can repeat this situation, can you take your volt-meter and measure a voltage drop  between the battery plus terminal and that wire ? 
I'll try to replicate the scenario and measure it when sun is up.  wiggling it by fingers now, the terminal block appears pretty firm.


CountryFit

Quote from: FNG on June 25, 2018, 07:39:12 AM
Not much to add to what Robin and boB said, The Classic was in float because the positive battery side likely has a bad connection, I would put a call in to tech support today and Kyle or some one can help you get fixed up
Gonna call them once they are open for business.

Westbranch

That really looks like the loose connection meltdown I had in my E-Panel.....ALL due to a loose connection when the classic was putting out ~ 50 Amps.

Did you re-torque the connections after 24 ~ hrs??
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CountryFit

#12
Quote from: Westbranch on June 25, 2018, 12:34:04 PM
That really looks like the loose connection meltdown I had in my E-Panel.....ALL due to a loose connection when the classic was putting out ~ 50 Amps.

Did you re-torque the connections after 24 ~ hrs??
I was certainly aware of the importance of the tightness and did tighten it a few times since 2 months ago. 
Maybe my current was too high - about 90A during the peak hours everyday when it was working.

Vic

Quote from: CountryFit on June 25, 2018, 02:08:10 AM
   ...
I discovered the overheat on the positive terminal 2 months ago. I slightly enlarged the size and inserted a 2ga wire   ...
Steve

Hi Steve,

It is quite possible that there was insufficient Torque on the original #4 AWG cable,  and that heating damaged the positive bat terminal of the Classic,  causing further heating.

I do not know if the Classic PV and battery terminals are Tin-plated aluminum,   or copper.   But,   reaming out the battery positive terminal,   would have removed any plating.   If the base material is Al,   that could well represent a very poor connection.

As Robin noted,  usually,  Tinning copper cable ends that terminate in screw terminals  is a bad idea.   The screw terminals  are designed to compress the cable strands,  which would increase the contact area and  reduce resistance.   The solder is not very compressible,   and could create more of a point-contact.

Please avoid tinning cable ends of screw terminal connections,  as well as for crimp terminals.

Just my opinions,   Good Luck.   BTW,   as you can see,   MidNite Engineering and Tech folks to listen,   AND give feedback.     Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

CountryFit

#14
Quote from: Vic on June 25, 2018, 02:21:13 PM

I do not know if the Classic PV and battery terminals are Tin-plated aluminum,   or copper.   But,   reaming out the battery positive terminal,   would have removed any plating.   If the base material is Al,   that could well represent a very poor connection.

The terminals appeared to be aluminum.  I saw the flakes when I reamed it.  After this time, I'll keep it as how it comes from the manufacturer.

Quote
as you can see,   MidNite Engineering and Tech folks to listen,   AND give feedback.     

I really like this board!  And very grateful for everyone's big helps!!
Steve