Parallel two solar controllers??

[thomm225]

As you can see in the links, open circuit voltage (OCV) is a term used in electronics circuits and batteries as well as with solar. Voltage Open-Circuit (VOC)

No load, no current flow. No ground so it's "floating!" At least that's how we tech's used to classify it

https://www.electrical4u.com/open-circuit-voltage/

https://en.wikipedia.org/wiki/Open-circuit_voltage

This is all I was referring to when folks freaked!

Simply attempting to allow others to see into the solar world and make it less complicated for some.

I assumed folks might know about Open Circuit Voltage (OCV) since electronic circuits have been around so much longer than solar and it was a common term

[thomm225]

Originally Posted by s/v Jedi

Yeah, he clearly knows what it is but just got the wrong term “floating voltage” in there and puts heels in the sand now… doesn’t work with EE’s abound

Could simply be a language thing.

BA History here!

Our logic classes were dealing with complete sentences which is the same but different than Boolean Logic. (or for that matter gate logic in electronics and computers)

That complete sentence logic taught in the Philosophy Department when I was getting my History Degree was a lot of fun though after years of Boolean and gate logic endured during years of electronics/computer training.

It was a graduate degree course but could be used for undergrads as well and the majority of the students were those wanting a law degree.

[s/v Jedi]

Originally Posted by thomm225

Well I used the term floating voltage correctly earlier, but it just threw folks for a loop who didn't have the background I have in electronics/computers etc. I could have worded the statement a little better though

Voltage Open Circuit (VOC) in solar or floating voltage in electronics is basically the same though since there is no circuit flow. I simply thought to add that thinking it may help others understand better

As far as the Octopus and Huntron Trackers, we used those to troubleshoot and repair circuit boards when there were no schematics available or when the systems were being used and we couldn't install the board on an extender and troubleshoot it with an o'scope and schematics but had to troubleshoot on the bench instead.

We also called a voltage floating with TTL circuits. If say one output of an IC was 2 volts we said it was floating.

It should have been a high (5 volts) or a low ground or 0. TTL was used for the early binary 1's and 0's circuits so they could count later used by computers.

Another definition of float in electronics was when a circuit, system or unit wasn't grounded. It was said to be floating.

Like all the systems on my boat, there's no ground to the engine then to the sea thru the prop as before.

In the photos, I was low on battery power so hooked up my two 20 watt panels directly to the batteries and was monitoring the voltage with the meter and on one of the PWM controllers with a display

All panels were getting max Sun light for the most part. None of my panels are permanently mounted so I can aim them directly at the Sun if I need to.

The full 155 watts of panels that I had are hooked up. Two 20 watt panels direct, my 10 year old 65 watt panel, and a Renogy 50 watt panel thru controllers

The 20's and the 65 are attached using some old 14 gauge wire we had left over from another project.

I see where your confusion comes from. You confuse an open circuit with an “un-tied” circuit. Yes, a TTL output of 2V is called a floating output (-not- floating voltage) and happens when the IC is defective. Floating inputs are much more common and must be prevented by pull-up or pull-down resistors. Note that it is called a floating input, not a floating voltage.

When a power carrying network is called “floating” we do speak of “floating power”, “floating voltage” etc. but it has nothing to do with being open circuit or not having current because it actually is connected and is carrying current because it could not carry power otherwise. The reason for including the term “floating” is that the DC negative (or positive in some cases) is not connected to ground or that none of the AC conductors is connected to ground. This means it’s potential is not “tied down”, not “anchored to”, not “referenced off” ground, where ground may be earth or chassis.
Same for TTL gates: when you add the pull-up resistor to Vcc, the input doesn’t float anymore because when you remove the circuit from the input gate, the resistor makes it equal to Vcc or high.

A floating voltage is ungrounded but it is connected and not open.

[thomm225]

Originally Posted by s/v Jedi

I see where your confusion comes from. You confuse an open circuit with an “un-tied” circuit. Yes, a TTL output of 2V is called a floating output (-not- floating voltage) and happens when the IC is defective. Floating inputs are much more common and must be prevented by pull-up or pull-down resistors. Note that it is called a floating input, not a floating voltage.

When a power carrying network is called “floating” we do speak of “floating power”, “floating voltage” etc. but it has nothing to do with being open circuit or not having current because it actually is connected and is carrying current because it could not carry power otherwise. The reason for including the term “floating” is that the DC negative (or positive in some cases) is not connected to ground or that none of the AC conductors is connected to ground. This means it’s potential is not “tied down”, not “anchored to”, not “referenced off” ground, where ground may be earth or chassis.
Same for TTL gates: when you add the pull-up resistor to Vcc, the input doesn’t float anymore because when you remove the circuit from the input gate, the resistor makes it equal to Vcc or high.

A floating voltage is ungrounded but it is connected and not open.

I'm going to let the argument drop as I can see both sides.

Also I have been a manager of Techs (hardware, software, plus cyber more recently) since 1995 and don't get to do what I'm hardwired to do which is logic troubleshooting of electronics and computer problems as often so I'm definitely rusty.

Playing around with solar on my boat has really been a lot of fun. (even though my Victron MPPT 75/15 failed possibly from all my mixing of controllers and panels plus constantly connecting and disconnecting them)

Maybe this description off the internet will get across my point as to why I refer to the VOC or OCV as floating:

"Floating voltage describes any voltage which is not tied directly to a fixed reference. This is usually earth or ground depending on which term is used where in the world you live."

What is a floating voltage? - Quora

I destroyed the back of one of my panels once when it got blown off the boat when it was in the yard. After I repaired it, I saw the plate on the back and noticed the VOC voltage. So I measured the panel's output while disconnected from everything

In my head the panel was "floating" as it wasn't connected to ground or any circuit and of course I got the VOC or something close. Plus it was definitely an open circuit as there was no current flow. Nothing was hooked to the panel.

Like when you test a new panel for VOC as soon as you take it out of the box. It's just the panel alone......floating! (and the circuit is open because there is no circuit except the one created when you attached the meter......hopefully the meter circuit doesn't cause more confusion! (as it's super high impedance)

So I interchange the wording as it seems to fit but as I mentioned when I used the float word earlier it can cause confusion when introduced within a solar discussion

[goboatingnow]

As a recently retired EE I fully support Nicks post on explaining panel dynamics

Secondly the term floating voltage is never used out side of batteries where the term refers to the “ float “ part of battery charging

Ungrounded circuits are indeed “ floating “ but the term floating voltage is meaningless. Please stop respectively justifying a mistake. If you learnt this term , in that way , in your EE career it’s simply wrong. The term “ open circuit voltage “ is common place and well understood . The term “ the logic input /output is “ floating “ is also used but again this is a specific context

Could I make a few points

A PV panel is not a battery , it’s not primarily a voltage source it’s actually more equivalent to a current source. People get confused around current sources

More importantly for PV panels the relationship between Vout and Iout is not linear over a series of illuminations , this is because the transfer function is not linear.

That’s means there exists a “maximum “ power point that for a given level of illumination where a particular voltage operating point results in maximum current , ie max power.

This is what mppt controllers do , yes unlike PWM they convert from higher voltage lower current to lower voltage higher currents ( known as buck conversion ) but MPPT controllers move the conversion point to ensure the best power transfer for a given illumination. ( this is essentially done at a theoretical level by changing the input resistance of the buck converter )

So yes you can connect PV panels of any voltage directly to a battery as they are current sources but of course you get an inefficient power point and the issue also is as the current tapers off , the panel power point moves the voltage up , potentially damaging the batteries.

Since the VMp also decreases with increasing panel temperature you can find that mppt controllers are very ineffective over pwm where the panel array voltage is only a few volts above the battery , hence mppt is more effective for higher voltage arrays

The other thing is mppt controllers only work effectively if the load , or the battery is pulling power close to the max point of the panel in the first place. If the battery isn’t loading the panel mppt doesn’t actually offer any benefit.

[kmacdonald]

The technicalities mean little to nothing to the average boater. The science has already been done for us. Just read the data sheets and chose the equipment accordingly. It's really that simple.

[mitiempo]

Originally Posted by kmacdonald

If you read the data sheet for the victron solar charge controllers it clearly say exceeding pv short circuit current rating of the controller may damage it. For the 75/15, it is 15 amps.

True but hardly ever an issue.

[thomm225]

It's always enjoyable to discuss old school electronics.

I for one certainly miss it whether you agree with my terms or not my training has served me well.

Solar is the closest thing to the old DC Circuits that I can find which is why I enjoy it so much.

I may instead of installing some sort of small bimini on my boat install a support for a 100 watt or higher panel and have that be the Sun blocker plus charge the batteries

These days it's all about computer certs, software to include Linus OS, and cyber security which will be the next thing all techs will have to be certified in

[s/v Jedi]

For anyone wanting to learn about solar panels, controllers and practical applications on boats: first go here: https://www.victronenergy.com/upload...WM-or-MPPT.pdf

then to find controllers matching your panels, go here:
https://www.victronenergy.com/mppt-calculator

[thomm225]

Also if you get the Victron 75/15 or any Victron Controller, I would recommend getting the one with bluetooth. It's a little more expensive but worth it.

I still had a flip phone when I bought mine so I got the cable and adapter.

It was a PITA.

So as I have an iphone now my next controller will be a Victron 75/15 with bluetooth so I can monitor the panel(s) so much easier.

I may have it as the controller to my 12 volt backup battery and allow my older panels and PWM controllers to charge the two 6 volt golf cart batteries I have.

Or vice a versa

[goboatingnow]

Originally Posted by kmacdonald

The technicalities mean little to nothing to the average boater. The science has already been done for us. Just read the data sheets and chose the equipment accordingly. It's really that simple.

True , but if you understand the first principles it’s let’s you understand what’s happening , or not , let’s you evaluate how your system performs against theoretical maximums and let’s you intelligently debug you’re system when it doesn’t work.

[goboatingnow]

Originally Posted by s/v Jedi

For anyone wanting to learn about solar panels, controllers and practical applications on boats: first go here: https://www.victronenergy.com/upload...WM-or-MPPT.pdf

then to find controllers matching your panels, go here:
https://www.victronenergy.com/mppt-calculator

That first link is a great panel summary and should be read by anyone with PV panels

[skipmac]

Did a preliminary test with one of the new panels today. Batteries were already fully charged, in float made accepting less than 1% of the bank capacity. Disconnected all charging sources, ran some large loads for about an hour to drop the voltage a bit so the controller would go into bulk charging mode.

Connected the panel. By that time it was well after midday and the panel was partially shaded by the mast. Still was able to see 15 amps output until the battery voltage jumped back up.

Based on this I'm pretty sure I'll see well over 20 amps with the batteries discharged and good sun on the panel

[s/v Jedi]

Originally Posted by skipmac

Based on this I'm pretty sure I'll see well over 20 amps with the batteries discharged and good sun on the panel

Ha! Iirc my math said 22.22A to hit rated capacity

[noelex 77]

Originally Posted by skipmac

Did a preliminary test with one of the new panels today. Batteries were already fully charged, in float made accepting less than 1% of the bank capacity. Disconnected all charging sources, ran some large loads for about an hour to drop the voltage a bit so the controller would go into bulk charging mode.

You don’t have to deplete the batteries or wait to measure the maximum solar output (in watts). Just put on a load greater than the array wattage.