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Solar Charge Controller displays different voltage than at battery

For PV, a clamp ammeter with DC (not just AC) amps scale is very handy.
I just bought one from Harbor Freight for $100, but I think people have found $30 models.

What I was looking for was 0.01A resolution so when reading a PV string that produces about 1A due to low sun angle, I'll have 1% resolution and 5% accuracy.
Also 600A or higher for my battery.
The meter I got has 1000A, 600.0A, 60.00A scales.
 
Im wondering if I should just buy the shunt that digitally detects the battery AH, shows the level, percentage and volts correctly


Coulomb counter could be convenient.
For same price, a DMM could be used to debug other things.


I just got it, don't know how durable.
I've had my Fluke for 20 years. A comparable range clamp meter from them was 4x the price and didn't have the resolution I wanted.

 
So tonight I come home and now it's fully charged...at battery it shows 13.1 and controller 12.9 and battery diagram full
 

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Only as accurate as your panel meter.
Here's one spec'd at 1%, so 13.1V reading could be 12.97V


Normally, accuracy is quoted as a percentage of reading plus a percentage of range (or so many LSB counts)
For my new meter, "(@60mV-600V) ± 0.5% of rdg + 5D"


Because your panel meter has so few digits, there is a chance that's 1% of reading +/- 1 count, if its ADC is 12 bits (one in 4096) rather than 10 or 8 bit.
Some meters have 6 1/2 digits but are only accurate to about 4 digits (drift over time but useful to see small differences short term.)

The Fluke clamp meter I linked was 2% +/-5 counts for current, 1% +/-5 counts for DC voltage.

It would seem 1% is barely good enough for lead-acid batteries, because we want to fully charge them. For LiFePO4 people might think they want better accuracy, but maybe balanced to 3.65V and operated to 3.4V it doesn't really matter there either. So long as automatic balancing keeps cells within 1%. Enough digits on DMM should confirm that even if absolute accuracy isn't better. Staying 0.2V away from upper end of knee (5%) is quite sufficient.
 
Currently I am using 12 awg cable to the battery, I have ordered 10 awg and I will see how that goes, I would like to get a more accurate reading if possible.

Thanks for your help guys I will keep you updated
 
Changing to a thicker wire won't change much with the voltage readings. All the displays you have recording voltage to 0.1 of a volt will easily record plus or minus 0.1 on the actual reading. Low cost displays like the meter on the USB socket are often in error by up to 0.4v on a 12 volt system. To see the actual voltage you need a reasonable quality meter.

Its possible to test against a stable voltage reference,


With your new AGM, if its showing just over 13 volts with no load or charge following a rest period, then its fully, or almost fully charged.

Mike
 
what their batteries display...is it just me with this issue?

sorta; it’s you but not just you.

I use 8awg for charge controller to batteries. Most good small system solar charge controllers will take 8ga some will take 6ga.
I used to see a .1 to .2V variance from dmm to charge controller with 10ga. When I changed to 8ga it is .1

The readout on my epever right now is vacillating 12.5/12.6. The readout on my inverter is 12.5. The readout on my usb charger fed from my Blue Sea fuse box is vacillating 12.5/12.4. Are any of them wrong? Nope. And I suppose yes because they could be completely accurate where they are reading- or not.

I’ve seen car batteries hold charge at 12.8, 12.9, 13.1… They all worked just fine.
My solar charged deep cycle lead batteries have held 13.1 for a day or more if disconnected. But typically they’re anywhere from 12.9-13.0 to 13.1-ish but I’ve seen them 13.4 well after sunset (but now that I’m electric fridge that doesn’t happen anymore)

So I think “it’s you” in that you’re worried about it too much. Anything 12.8 to 13.4+ is “full.”

The shunt is I suppose a better indicator than the SCC. I don’t use one. With 2/0 cables to the inverter that readout’s close enough for me. With lead batteries no sleep should be lost over this.
 
Those cheap panel meters are not accurate. Expect +/- 0.2v error. Renogy is not good kit either. Get a DVM. Best plug in meter I found is this:
4 digit
 
I know I sound like a broken record, but the voltmeter/multimeter is not the area to skimp on when dealing with battery systems. Don't skimp on your system-reference.

Why? Aside from one-off terminal measurements which might be close enough for government work, successive comparisons with a variety of metering instruments down the line to be "eh, that's close enough" to it's nearest neighboring meter when compared to each other, can lead to consecutive resolution errors that add up.

This is even more critical with lithium-based battery systems.
 
Ok guys so even more confused now ...at battery and at controller terminals connection both were reading same 12.59/12.6 but controller itself at is reading 12.4 :(

I recently got a refund for the controller as it cycles through the menu constantly where it should be steady on the main menu (showing the pv and voltage status but it doesnt just continues to cycle and now I'm wondering if it's actually a faulty unit in more ways than 1.
 

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Battery voltage is decent (for AGM), SCC display is way off. Have to consider "12.4" to mean 12.3V < reading < 12.5V
Probably means its settings are off as much.
Measure and observe how high it charges battery, decide if actual performance is acceptable or not.
If not, upgrade to some other brand.
 
I have a Rover 40a CC. Currently sitting in float it shows 13.8v on the display, met DMM shows 13.98v at the battery terminal connections on the CC and the two digital panel meters I have in a couple of spots in the RV show 14.0v. There is currently a pair of 6v AGMs in the system. I asked Renogy about it a couple of years ago and even with a thread on their tech board there was no real answer for the difference.
 
They all use an internal voltage (bandgap) reference. They are not born accurate, they have to be trimmed $$$, or not. It's amazing that cheap junk is coming in below +/- 2% error. That's great wafer process control.
 
They all use an internal voltage (bandgap) reference. They are not born accurate, they have to be trimmed $$$, or not. It's amazing that cheap junk is coming in below +/- 2% error. That's great wafer process control.

The silicon foundries are huge and do have good control.

The stuff I designed, I used an ADC that could convert 4x per second up to 800x per second with varying bits.
We calibrated assembled boards with externally applied signals where it mattered (store a point-slope or other correction in EEPROM.) That's what these guys ought to do.
For better performance I used a separate voltage reference IC (which cost $10 or $20), not for battery charging applications of course.
The balance of components have to be of suitable quality and the design done carefully. I used resistors costing $0.04 in moderate quantity (for 0.1%) and others costing $20 each in small quantity (for ppm level.)

Here, we're talking about a charge controller selling retail starting at the price of a single IC I used:




My concern for these charge controllers is whether they charge an AGM battery to the correct voltage. It's lifespan totally depends on that.
Need to measure what absorption and float voltage it reaches. Replace with something else if not correct.
 
Battery voltage is decent (for AGM), SCC display is way off. Have to consider "12.4" to mean 12.3V < reading < 12.5V
Probably means its settings are off as much.
Measure and observe how high it charges battery, decide if actual performance is acceptable or not.
If not, upgrade to some other brand.
Well the issue is all it's auto settings are dependable on what volts it detects. So if it thinks it's less and wayy less than the float boost cut off and so on are all gonna be out right? :(
 
This is also my concern!

My concern for these charge controllers is whether they charge an AGM battery to the correct voltage. It's lifespan totally depends on that.
Need to measure what absorption and float voltage it reaches. Replace with something else if not correct.
 
Well the issue is all it's auto settings are dependable on what volts it detects. So if it thinks it's less and wayy less than the float boost cut off and so on are all gonna be out right? :(

There is a chance the meter portion doesn't know what the charge controller portion is doing.
Distrust, and verify.

Once you see battery voltage during bulk/absorption/float you'll know if it is OK or not.
 
This is the latest :/ seems they agree that their is an issue with I guess a part that the controller use.

Interesting fact I met a guy on the weekend with the other rover charge controller and he too confirmed it did his head in for ages not understanding why the controller shows the I correct voltage.

Anyway read the email attachment from RenogyScreenshot_20210623-204101.png
 
There is a chance the meter portion doesn't know what the charge controller portion is doing.
Distrust, and verify.

Once you see battery voltage during bulk/absorption/float you'll know if it is OK or not.
Above is from post #38. Below is post #7
So the charge controller could be right in being 12.7 if the batt is reading 12.8?

When you say adjust the settings,…..
I have agm

So as far as the ability to charge: did you distrust and verify the float, absorption, and equalize voltages?

I think you’re obsessed with the numbers displayed and thereby missing out the important part: is it working correctly? You have to apply the human intelligence factor to the readouts. It’s like with a HF/Pittsburg digital measuring tool I have: it says it has resolution to 0.0001” but it’s label says it’s accurate to +/- 0.005”. You don’t use it to measure crankshaft journals or ceramic bearings in other words.

Your AGM is tolerant of a relatively wide range of charging voltages. What the readouts say is probably good daily reference BUT to prove everything is fine the “verify” part is the only thing that matters. Up until then it’s splitting hairs or semantics.

I never worried about (the variances I experienced) mine because I’m used to variances among even the same model of electronic devices- seen it so many times.

it’s good for renogy to know I guess but seriously: they ain’t gonna reinvent that controller. It was probably a purchase order with a lower failure rate spec, not actually engineered by renogy.
 
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