Charging issue with thermal circuit breaker? SOLVED

[ohiomoto]

I'm using a 50a T Tocas thermal circuit breaker on the output side of my 40 DC/DC charger.

I am getting a drop of nearly 1 volt at the breaker. So instead of charging at 14.4v, I'm getting 13.5v max. (I assume I'll be having the same issue with my Victron 100/30 as it has a 40a Tosca breaker on it.)

I assume this means I'll never reach a full charge on my battery (300Ah Enduro Power)?

Any suggestions?

EDIT: I was mistaken. There is no issue. Post 12 is what I have learned and I confirmed this with Renogy tech support. At this point, my charging system is working correctly.

I believe I was mistaken when I thought the breaker was causing a voltage drop. I think I was simply reading the battery voltage on that side of the breaker and mistook that as my charging voltage.

 

[John Frum]

Could be the breaker, or it could be the joinery to/from the breaker.
Can you bypass the breaker for a test?
While you bypass the breaker you will be the breaker.
That means stand buy with fire extinguisher and wire cutters.
Of course to make a good test you will need to put the same amount of current through the circuit when you measure the voltage drop along that part of the circuit.

 

[ohiomoto]

It is the breaker. I measured 14.4v on the input and 13.5v on the output of the breaker. I'm sure it will charge at 14.4v if I bypass it.

Is this a faulty breaker? A common problem with thermal breakers? Should I get a different breaker or fuse? Do I really need a breaker on a 12" run of 4g wire (assuming it's protected from physical damage)?

 

[John Frum]

It is the breaker. I measured 14.4v on the input and 13.5v on the output of the breaker. I'm sure it will charge at 14.4v if I bypass it.

Is this a faulty breaker?

That is what we are trying to ascertain by testing.
A 1 volt drop across a breaker at 40 amps sucks.

A common problem with thermal breakers?

With cheap breakers, yes.

Should I get a different breaker or fuse?

lets try the test first.

Do I really need a breaker on a 12" run of 4g wire (assuming it's protected from physical damage)?

Yes each circuit should have over-current protection.
I like fuses for the core.
The means of disconnect should be a double pole switch on the pv side of the solar charge controller.

 

[ohiomoto]

Bypassed the breaker and the charger output dropped from 14.4v to 13.9v but that 13.9v was carried all the way to the battery. The battery voltage drops to 13.5v when I turn the van off.

I assume the 13.9v is the "average" of the battery state of charge plus the 14.4v charge current?

And should I expect that number to go up as the SOC goes up?

 

[John Frum]

Bypassed the breaker and the charger output dropped from 14.4v to 13.9v but that 13.9v was carried all the way to the battery. The battery voltage drops to 13.5v when I turn the van off.

You have 900vm drop in the first test and 500mv in the second test.
500mv is better but its still not good.
You should be testing from the same points for both tests.
Please post a picture of the positive lead indicating the measurement points for both tests.

What awg is wire is the positive lead?

I assume the 13.9v is the "average" of the battery state of charge plus the 14.4v charge current?

And should I expect that number to go up as the SOC goes up?

Lets focus on the voltage drop over the dc2dc charger negative wire until we get that sorted.

 

[Hedges]

"Fault" - "T-Tocas" I think qualifies as that.

It is the breaker. I measured 14.4v on the input and 13.5v on the output of the breaker. I'm sure it will charge at 14.4v if I bypass it.

Measured on the studs of the breaker? Or the wire terminals?
Make sure you do not have any washers between wire terminals and breaker terminals.

Quality brands are the way to go, but those too can be connected incorrectly.
There are some decent brands of lever-action breakers. Thermal only, no fast magnetic trip.
Not as bad on a charger circuit as inverter circuit, but you might want a fuse holder instead.

 

[ohiomoto]

Measured at the studs and wire terminals. Same 13.9v at various points of the system since bypassing the circuit breaker. Pulling 14.39 volts at the input side of the DC/DC charger and it's producing the rated 40 amps.

Windy Nation 4 AWG copper wire. The negative is terminated on the load side of my BMV-712 shunt along with the negative from the 100/30 Victron SmartSolar charge controller. The positive wires terminate at the battery side of my main fuse.

No loads on the system, just the battery, shunt, MPPT, DC/DC, and an empty 12v Blue Sea fuse block.

 

[ohiomoto]

Lets focus on the voltage drop over the dc2dc charger negative wire until we get that sorted.

Do I have a negative wire voltage drop or am I reading the battery voltage?

Hence the questions below:

Bypassed the breaker and the charger output dropped from 14.4v to 13.9v but that 13.9v was carried all the way to the battery. The battery voltage drops to 13.5v when I turn the van off.

I assume the 13.9v is the "average" of the battery state of charge plus the 14.4v charge current?

And should I expect that number to go up as the SOC goes up?

These questions are important to me because I'm not one to chase a problem until I'm sure it exists. Should I really be reading 14.4v on the battery side when the battery is currently at 13.5v?

If the answer is yes, then I will proceed.

EDIT: @John Frum, I really appreciate the help. Please don't take the comment above as me being difficult.

 

[740GLE]

Pictures are worth a 1000 words toss some up!

 

[ohiomoto]

With the breaker bypassed the output of the charger gradually rose to 14.35v as the battery voltage gradually rose to 14.35v.

I think I might have answered my own question.

Bypassed the breaker and the charger output dropped from 14.4v to 13.9v but that 13.9v was carried all the way to the battery. The battery voltage drops to 13.5v when I turn the van off.

I assume the 13.9v is the "average" of the battery state of charge plus the 14.4v charge current?

And should I expect that number to go up as the SOC goes up?

I'm no electronic wiz kid, but it looks like the measured voltage output of the charger is based on the current SOC on the battery. This makes sense to me because this is simply a voltage drop, no?

Did I get tricked in my original question?

I am getting a drop of nearly 1 volt at the breaker. So instead of charging at 14.4v, I'm getting 13.5v max.

Maybe I should have written "I'm reading a drop..." instead of "getting" and "..measuring 14.4v..." instead of "getting".

I measured 14.4v on the input and 13.5v on the output of the breaker.

Is the discrepancy simply the difference in voltage on the two poles of the breaker base on what's on that pole? Do breakers isolate those two poles?

I'll put the breaker back in play and test again, but I wonder if there is actually a problem here besides my expectations and lack of understanding.

Any thoughts?

 

[ohiomoto]

I put the breaker in question back into service and I'm now seeing 14.34v to 14.35v at all points in the system.

I believe I was mistaken when I thought the breaker was causing a voltage drop. I think I was simply reading the battery voltage on that side of the breaker and mistook that as my charging voltage.

This was confirmed by Renogy tech support.

 

[Hedges]

Take multiple measurements, voltage at battery and voltage at SCC terminals. Measure voltage across breaker.
That will show things an expert can't guess from a distance.

You previously reported 1V drop across the breaker terminals. Could be there is a lot of resistance, so voltage drop with current flow. But 1V at 30A would be 30W, and the breaker would be smoking.

Photos help. We've seen washers under screws, DMM probes in wrong socket, many things missed by the user.