Classic 150 voltage readings

[mtdoc]

Where are you measuring battery voltage and with how good of a meter?  Is the voltage measured with your meter at the Classics input terminals different that what it measures at the battery terminals themselves?  If lower at the classic - perhaps you do need larger or shorter cable or need to check your connections.

FWIW  my Classic's voltage readings are within 0.1 V of what I measure at the batteries with a good meter.

[jimbo]

I'm measuring the voltage with a cheap multimeter AND my SunnyBoy inverter under no load and both are identical.

When there is little to no sun the classic, inverter and multimeter all match up, however while there is a fair bit of current going from the classic to the battery the classic is reading 0.5v HIGHER than both the inverter and multimeter.

[mtdoc]

Well if the Classic is reading higher than the batteries measure at the battery terminals then its hard to blame it on too long or to small a gauge wire to the batteries.

For a check have you measured the voltage at the Classics battery terminals?

[jimbo]

Not yet

[Halfcrazy]

When current is flowing and you have the 0.5v discrepency get these 3 values and report back:

Battery V as read from the classic display:
Battery V as measured on the Classics terminal block with a meter:
Battery V as measured on the battery terminals with a meter:


Ryan

[jimbo]

Ok will do.  Just need some sun....weather has been terrible!

[dbcollen]

I'm measuring the voltage with a cheap multimeter AND my SunnyBoy inverter under no load and both are identical.

When there is little to no sun the classic, inverter and multimeter all match up, however while there is a fair bit of current going from the classic to the battery the classic is reading 0.5v HIGHER than both the inverter and multimeter.

If you are reading higher voltage on the classic when it is putting out substantial current, then you have a high resistane connection, or you wire is too small. While you are experiencing the volt drop, feel the insulation on the wires, if one is warm, than tighten its connections. If that doesn't work, than upgrade to bigger wire.

I just had the same issue, one of my charge controllers started reading 1v higher than everything else when charging. I felt the wires and the negative wire was warm, it is under a foot long, 6awg and only carrying 25a. It was quite warm, turns out the screw holding the wire in the busbar was loose because the stranded wire crushes. That is a common problem with stranded wire, the finer the strands, the worse it is.

[mtdoc]

Good catch dbcollen. Somehow I totally missed the part about the Classic's reading being higher only when it is putting out high current. It makes more sense now!    I would still measure voltage at the Classics battery terminal to help narrow down the problem. A voltage drop there when at rest would help confirm a problem with wire or connection from battery.  If there are other connection points between classic and battery bank (bus bars, etc) checking there as well could help pin it down.

[dbcollen]

The voltage drop is a function of resistance and current, the more current flowing through a given resistance, the more voltage drop there will be. When the controller is not charging it should still read volts accurately if there is a high resistance connection.

[jimbo]

With offset set to 0 and around 35-40 amps going into the battery

Battery V as read from the classic display: 28v
Battery V as measured on the Classics terminal block with a meter: 27.9-28v
Battery V as measured on the battery terminals with a meter: 27.6v

Like the other have said i do think it is a wiring issue.  The wire run to the batteries is around 2ft but is not 100% ideal as i have replaced 2 controllers with one and done a bit of 'massaging' with the wires to get them in the terminal block. I will replace them some time this week and see what happens.

[mtdoc]

2 feet is not a long distance for a wire run to the batteries. The issue is likely the connections. You may want to replace the wire though. If 50 amps is about the max you will be putting out of your Classic 6 AWG would be plenty large enough. Bigger is always and you can get 4 AWG into the Classic terminals  with a little finesse (but unnecessary for 50 amps) The connections are really the key.

[jimbo]

I see 63 amps when the batteries are low and the sun is shining and hoping to add some panels this week to bring it closer to 90 amps. Might as well use the biggest wiring possible as it is such a short run.

So with wiring up to spec does anyone else see a different voltage at the battery terminals to the terminal block under heavy charge?

[boB]

What kind of volt meter are you using to verify ?
It might be that the Classic measures voltage a bit
differently than your meter does.

Also, you might also try to connect the meter probes to a piece of exposed
copper going into the terminal block rather than the screw itself.

boB

[TomW]

With a cable that short, can you measure the voltage across the cable? As in from Classic terminal to the battery terminal? Under heavy charge will show any significant drop due to cabling / connections quickly.

Set for a low range this will show any drop from cable losses. And the quality of the meter or calibration differences will not be an issue.

Just an idea.

Tom

[jimbo]

I have had the cables upgraded to the battery and there is still a 0.4v difference while charging at anything over 50amps.