Better wire for solar panels -> charge controller?

[dwh]

Maybe you need to go measure the voltage of your system at the output of the solar panel and the input to the controllerwhen it is running 10 amps and see for yourself.

In other words...

Create short circuits bypassing various sections of the loop and see if I get different readings on different short circuits.

Which, of course, I would.

None of which would measure what the entire loop happens to be doing.

Of course since we are talking voltage drop in the wires it will be a very small voltage.

You still dont get it. The wire resistance is going to manifest as a current drop on the charging loop, not a voltage drop, because the battery is regulating the voltage of the loop.

 

[dwh]

So for battery charging, you dont need to upsize the wire to compensate for voltage drop that doesn't exist anyway.

You upsize the wire to compensate for current drop, which does exist.


Having said that, it should be noted this applies to charging the battery. Feeding a load, such as an inverter, from the battery is a different situation.

Internet voltage drop calculators are all designed with the basic assumption of feeding loads, not with the basic assumption of charging a battery.

Which is close enough most of the time that it won't hurt anything..other than misleading people into thinking that voltage drop always exists.

 

[verdesardog]

So for battery charging, you dont need to upsize the wire to compensate for voltage drop that doesn't exist anyway.

You upsize the wire to compensate for current drop, which does exist.


Having said that, it should be noted this applies to charging the battery. Feeding a load, such as an inverter, from the battery is a different situation.

Internet voltage drop calculators are all designed with the basic assumption of feeding loads, not with the basic assumption of charging a battery.

Which is close enough most of the time that it won't hurt anything..other than misleading people into thinking that voltage drop always exists.

haha ****** is current drop????? A reduction of current flow will be only be caused by a reduction of voltage or increase of resistance. I=E/R. If R=0 you would have infinite current. I'm not even going to look at this ridiculous thread any more.

 

[dwh]

A reduction of current flow will be only be caused by a reduction of voltage or increase of resistance.

Or.

Exactly what I've been saying.


And I guess you find it unacceptable to refer to a "reduction in current" as a "current drop" ...

Offends you does it?

Good.

As offensive and insulting as you've been, I'm happy to return the favor.

 

[dwh]

http://support.morningstarcorp.com/...WM-vs-TrakStar-MPPT-Whitepaper-March-2015.pdf

Guys...

Read what it says about pwm charging. Read it again until you understand it.

What they describe (array voltage pulled down to battery voltage, array operating at battery voltage), is exactly the effect I've been describing.

Now I suppose someone might argue that Morningstar doesn't understand how their stuff actually works...

Yea...right.

 

[dwh]

What they describe (array voltage pulled down to battery voltage, array operating at battery voltage), is exactly the effect I've been describing.

And yes...while that's happening you can goof around and stick your meter across the terminals of the pv and you'll see a higher voltage.

Yea? So what? Big whoop. It don't mean jack. Fugedaboudit.

 

[dwh]

So if the battery is at battery voltage...and the pv is at battery voltage...then the wire must be at battery voltage...and that would mean that THE ENTIRE FRIGGING LOOP IS AT BATTERY VOLTAGE!

So...where is the voltage drop?

Nowhere. Doesn't exist in that situation.

Its all in your mind.

 

[haven]

Hey everyone, please bring the tone of your comments down a notch or two. Saying "You don't have a clue what you're talking about" or "Don't be so dense" doesn't advance your point, it just makes people upset. Thanks.

 

[dwh]

I'm not upset, I'm just hard-headed.

So...what's different about feeding a load from a battery?

Well you don't have an extra energy input source with a higher voltage potential trying to push up the loop voltage.

So you start out at the maximum voltage potential of the source (battery voltage) and it's all downhill from there.

The faster you extract energy the more the voltage of the loop falls.

So say a big inverter under heavy load. It might pull the loop voltage down to 11v, even though the battery itself is actually at 12v.

Wire that's too small will make the problem worse.

You can fool yourself with your meter. You measure at the inverter and see 11v and measure at the battery and see 12v.

So you think there is a voltage drop along a straight line from battery to inverter. Not so. There is a voltage drop, but the voltage has dropped around the entire inverter loop.

When you measure the battery, you bypass the inverter loop and read the source potential directly.

 

[dwh]

When you measure the battery, you bypass the inverter loop and read the source potential directly.

Same with charging. When you measure at the battery, you are seeing the actual working voltage of the charging loop.

When you measure at the source, you are bypssing the charging loop and seeing the potential of the source.

Apples and oranges.

 

[LeishaShannon]

Hmm. If you measure the voltage across one of the wires between the panel and the controller you'll measure the drop. There is voltage drop, but its irrelevant in a PWM solar charging circuit because PWM (or direct connection) pisses away the potential energy between Vmp and Vbatt anyway. (Unless you had grossly undersized wires that brought the Vmp down below Vbatt)

 

[dwh]

Hmm. If you measure the voltage across one of the wires between the panel and the controller you'll measure the drop.

Again, that's a measurement error, which i've already explained in detail.

First you created a short circuit, bypassing part of the charging loop, then you measured the voltage of that short circuit.

And sure, you can do that all over the place and get a variety of voltage readings which are all ultimately worse than meaningless because they are in fact misleading.

There is voltage drop, but its irrelevant in a PWM solar charging circuit because PWM (or direct connection) pisses away the potential energy between Vmp and Vbatt anyway. (Unless you had grossly undersized wires that brought the Vmp down below Vbatt)

No, there's no voltage drop in that situation.

And the effect I've described happens regardless if the battery charging loop is being fed by pwm, mppt, vehicle alternator or shore powered charger.

The only reason I mentioned pwm was to iilustrate the fact that the voltage is the same all around the loop.

 

[LeishaShannon]

Interesting. So if I stick a shunt/ammeter between the panel and the controller I won't measure any current (remembering an ammeter measures the voltage drop across the shunt...)

 

[dwh]

No, an ammeter shunt does *not* measure voltage. It has no way to do that, it's not grounded.

It measures current flow through a bypass loop.

All the resistor does is create a bottleneck in order to force a bit of current through the bypass loop.

 

[dwh]

https://www.bluesea.com/articles/552