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Solar Charge Controller displays different voltage than at battery

Nachjoe

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Joined
Jun 10, 2021
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18
Hey all for now months I've been trying to work this thing out with no luck currently after upgrading a few things this is what I have.

A brand new renogy elite 20a charge controller
Connected to a 170ah battery via 12agw cable about 1 meter long

On my charge controller the voltage displays around 12.6/12.7 volts but at the battery there is a voltage meter that shows 12.9 (fully charged)

For the life of me I can't work out what to do, it's annoying I have since last night purchase pending delivery 10awg cable from renogy as maybe some how there is voltage drop and I ha E also purchased their battery voltage sensor which connects into the regulator to get accurate readings regardless of voltage drop (nice little feature)

However any ideas? Anyone else experience this? Just annoys me I charge all day every day and want to come home seeing my controller tell me is charged but it doesnt.. however I know it is.

There is no load on it btwPXL_20210607_114250202.jpg
 
So put a digital multimeter on the battery terminals?

And if that's the case how the hell does anyone else sort this out, especially when the controller functions values like disconnect and recharge ect from what it reads.
 
So put a digital multimeter on the battery terminals?

And if that's the case how the hell does anyone else sort this out, especially when the controller functions values like disconnect and recharge ect from what it reads.
You need to know which one is off and note how much the one doing the controlling and adjust your settings. In digital voltage meters, the last digit is always +- one digit no matter how accurate the meter is.
 
You need to know which one is off and note how much the one doing the controlling and adjust your settings. In digital voltage meters, the last digit is always +- one digit no matter how accurate the meter is.
So the charge controller could be right in being 12.7 if the batt is reading 12.8?

When you say adjust the settings, on this controller it is very basic (auto detects) and only adjustable if lithium I have agm
 
So the charge controller could be right in being 12.7 if the batt is reading 12.8?

When you say adjust the settings, on this controller it is very basic (auto detects) and only adjustable if lithium I have agm
Which battery did it autodetect and did it autodetect the right one? 12.7 volts for a lead-acid bat at full charge seems low.
 
Usually the charge controller will charge at. Slightly higher voltage than the battery. Usually charge controllers have settings to calibrate the voltage display reading. As explained above use a multimeter to confirm ctuall voltage. Then you will know and can go from there
 
Usually the charge controller will charge at. Slightly higher voltage than the battery. Usually charge controllers have settings to calibrate the voltage display reading. As explained above use a multimeter to confirm ctuall voltage. Then you will know and can go from there
Ok will do.

Anyone else keen to share what their regulators display?? And what their batteries display...is it just me with this issue?
 
Ok will do.

Anyone else keen to share what their regulators display?? And what their batteries display...is it just me with this issue?
Could be as simple as different things showing different voltages. .1 or .2v isn’t much. Everything can’t be exact. But once you use a multimeter you will know what’s right
 
12.6 and 12.9 are basically the same thing. Not to a battery, but as a measurement. You need resolution at least 4x, preferably 10x beyond the quantity you're trying to measure. And accuracy, too.

Does your hand held meter only register 12.9? You need at least 3 1/2 digits so it can read 12.87, and if it is accurate you can be confident it is somewhere between 12.85 ad 12.89

Data sheet says, "Temperature Compensation: -3mV/℃/2V" - (Apparently per cell) wonder if its ADC has enough bits to resolve 18 mV, even though it doesn't display it?


Doesn't look like you get to adjust the values. At least it uses a battery temperature sensor.


I'm also using AGM. Recommendations vary somewhat between manufacturers.
Here are some of the battery parameters I get to change.
Voltages, times, temperature coefficient, etc.
Looks like I get settings down to 10 mV per cell which would be 60 mV per 12V, not that different from your 100 mV.

Sunny Island battery parameters.jpg
 
Could be as simple as different things showing different voltages. .1 or .2v isn’t much. Everything can’t be exact. But once you use a multimeter you will know what’s right
Yeh you say that but then as someone mentions above they personally think 12.7 seems low for a fully charged battery
Will check with digital mm this weekend, still love to visually see others pics tho i feel like im crazy or something or no one else really cares about what theirs reads?
 
I keep seeing lower from my AGM car batteries. They may have a parasitic load. I've sometimes topped them. When I pull out and repurpose I do an equalization charge.

I see the Renogy which says 12.7V also shows a battery icon not full.
It takes hours to completely charge that battery.

Got a technical manual for your battery?
Here's mine:


To charge, it wants CC of 0.2C, CV 14.2 to 14.4V until current drops to 0.005C (about 2 to 4 hours), then float 13.2 to 13.4V
Some people say a longer absorption is needed.
 
Some further info
 

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12.6 and 12.9 are basically the same thing. Not to a battery, but as a measurement. You need resolution at least 4x, preferably 10x beyond the quantity you're trying to measure. And accuracy, too.

Does your hand held meter only register 12.9? You need at least 3 1/2 digits so it can read 12.87, and if it is accurate you can be confident it is somewhere between 12.85 ad 12.89

Data sheet says, "Temperature Compensation: -3mV/℃/2V" - (Apparently per cell) wonder if its ADC has enough bits to resolve 18 mV, even though it doesn't display it?


Doesn't look like you get to adjust the values. At least it uses a battery temperature sensor.


I'm also using AGM. Recommendations vary somewhat between manufacturers.
Here are some of the battery parameters I get to change.
Voltages, times, temperature coefficient, etc.
Looks like I get settings down to 10 mV per cell which would be 60 mV per 12V, not that different from your 100 mV.

View attachment 52393
I dont currently have a multimeter but I will get one this weekend and make sure it can read as you say, thnak you
 
If you have it set for AGM and have the temperature sensor connected and stuck to battery, that's the best you can do.
They say 30A fuse for 30A circuit; we would say 40A fuse because we don't want it to blow unnecessarily.

Since yours is 20A, at least 25A fuse and 12 awg (which isn't quite kosher), better 30A fuse and 10 awg.
 
I keep seeing lower from my AGM car batteries. They may have a parasitic load. I've sometimes topped them. When I pull out and repurpose I do an equalization charge.

I see the Renogy which says 12.7V also shows a battery icon not full.
It takes hours to completely charge that battery.

Got a technical manual for your battery?
Here's mine:


To charge, it wants CC of 0.2C, CV 14.2 to 14.4V until current drops to 0.005C (about 2 to 4 hours), then float 13.2 to 13.4V
Some people say a longer absorption is needed.
Im wondering if I should just buy the shunt that digitally detects the battery AH, shows the level, percentage and volts correctly

 
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