The Eco-w's new VOC limit

[JiminDenver]

The last Eco-w 20a controller came while we we camping. The first thing I noticed was it now comes in a printed box with graphics and the info on it. The second thing I noticed is on the box the VOC limit is now 45v, not 42v. The printed pamphlet inside still has 42v as the limit so I would double check with Eco-worthy before depending on it running a pair of 12v panels in series.

[JiminDenver]

I agree.

[BFL13]

The Voc rating for a 260w Hanwha panel is 37.84. My Hanwha 230w is 36.8Voc

So the Voc does go up with panel wattage but it could be you would run out of the new wattage limit at 275w before hitting the Voc limit?

[JiminDenver]

Not only does it open up the ability to use a pair of 140w panels, it will allow use of some of the higher wattage panels with higher VOCs.

The only cold testing I did saw a panel rated for 36v Voc go over 40v for a short time but I don't think I'd see that normally. It wasn't early with the sun slowly coming up but rather I took a cold panel out and aimed it at the sun at 10 am on a super cold and clear day, hooked everything up and pulled the cover off. That's not going to happen normally, even in the clouds the panel will produce something and warm itself up a bit.

Now I just need to figure out how to sneak a few 12v panels in cus if Honey sees them, I'm dead meat. lol

[BFL13]

Mendy must be from Nova Scotia, calling everyone, "Dear." 🙂

The general rule for Voc limit is to use the voltage coefficient on the Voc rating (for 25C) and get the figure for the coldest ambient you expect to be camping in, so 45 Voc is still borderline for a pair of 12s at 22 Voc each in really cold temps.

That rule must be just for the first minute after switching on/hooking up because the panel warms up fast in the sun no matter what the ambient is. I think 45 would be just enough to get away with it in many scenarios where 42 would not be though.

I would wait till the panels did warm up in the sun and then hook in the Eco-W to give a little more margin.

Good to know, thanks!

[JiminDenver]

I got a response from Eco-worthy.

hi dear,
sorry for that.
45V is correct.
and you can use that in series.
thank you
mendy

[BFL13]

Sounds good. Scientists like us can't be stopped! 🙂

[JiminDenver]

Correct, it is the Vmp or working voltage that the controller receives. When I run the test I'll make sure as many things are identical as possible but it wasn't always one of the controllers being the low one. Which ever one is low is cooler than the other so I'd have to say it is accurate. usually at that point I pull the second controller and put it back on the trailer.

[BFL13]

I don't think it is Voc that the controller gets as input with the Isc. ISTR when attempting discover what "panel voltage" was, I got 34Voc (of rated 37) where that 34 was temp related. Panel must be disconnected to read Voc.

But then connecting up and batteries being charged , forget all the numbers, but something like battery 13v and voltage at panel now 29v and 28.x at the controller intake. So that amount less than 29 to 28.x was voltage drop on that wire, but the 29 at the panel was from being dragged down by the batt voltage I think.

So no idea where the panel watts components of voltage and amps should be taken from.

Anyway, on two chargers on one bank, the bank will accept from the higher voltage charger or take more from it than the other if the other lower voltage charger is still above batt voltage enough for a "spread" to make any amps. All normal.

So with solar controllers having mystery voltages as we are discussing, what could make the two identical controllers unequal in voltage as seen by the battery?
- wiring panel to controller
-wiring controller to battery
-connections

Now how do you measure the amps from each to the battery? (I had this happen with two controllers last year when I tried to find out how many amps each was doing of the total seen on the Trimetric reading solar only--controllers had no amps readouts)

You need a clamp- on meter. If you try to insert a meter as part of one of the two wires from one of the controllers, that increases the R (meter has thin wires) between that controller and the battery so now all the amps are chased over to the other controller to do.

Switch meter to other controller's wire and all the amps are chased back over the other way! It always looks like the one being measured by the inserted meter is not doing its share. A clamp- on meter would not have that problem. The Eco-Ws have amp readouts so not sure if each would show correctly what it was doing of the total.

[JiminDenver]

Considering that the Isc and Voc comes into the back of the buck converter and what comes out is controlled by the MPPT program deciding what will best bring the batteries voltage up, you really don't know what the panel is doing.

I have noticed that the controller likes a slower rate of charge if it just wakes up and starts charging. Start low and stay gentle even though more is there. Put a load on and get the controller to ramp up the amps and it will stay ramped up until it switches out of bulk.

Another example is when using two, they don't share the load when charging once the battery starts tapering the acceptance rate. One controller will stay high while the other will drop down to a few amps. disconnect the low controller and the other will pick up the few amps if not too close to peak but not more. 15a between two becomes 15a on one.

So I think if you really want to know what the panels are doing, disconnect them from the controller.

[BFL13]

JiminDenver wrote:
Thinking about it I can do one better with a bit of side by side comparison. I'll set up both 245w systems, run them both at peak while keeping one controller cool and letting the other one heat up until I see a difference.

I get confused about the Eco-Ws watts read-out. Chicken and egg thing. The panel has watts but the controller reads just the battery voltage times the amps it is making as output.

The panel can be in full sun with the controller in Bulk showing 200w but a minute later it can have dropped to Float and be making half the amps it was and the watts figure goes down too. But nothing really happened to the actual panel wattage.

The controller's watts figure seems sort of incestuous to me. We don't really see what the panel wattage is that is affected by the panel temperature out there so I don't feel I know what is really happening.

I do see that the little MPPT demo it does shows what the actual panel Isc is. (Compared it to my own Isc take at the disconnected panel a few times--same amps.) So one check to see if it is doing the best it can wrt insolation (being at or above rated Isc) is just do the demo and see what the Isc is.

You can only complain if the watts are lower than you like if the Isc is at or above rating. Otherwise the insolation is low and that might be the excuse for having low watts.

[JiminDenver]

Thinking about it I can do one better with a bit of side by side comparison. I'll set up both 245w systems, run them both at peak while keeping one controller cool and letting the other one heat up until I see a difference.

[JiminDenver]

I think it has to get pretty hot before it clips. The only time it has been obvious for me was when the controller was exposed to the sun and dropped from over 12a to under 6a quickly. I do know it would have shut down had I left it there.

I'll has to see if I can get the controller to warm up in the shade by pushing 16+ amps for a few hours and then see if cooling it has a affect. Not as hot as it got in the sun but still pretty warm. I'll keep track of the temps so that if it is changed, I'll know how hot it has to get before any clipping happens. I suspect it wont happen unless I don't allow the back side to get ventilation. I've seen 15-17a for hours at a time and haven't had it overheat yet.

BTW no response yet but it is the weekend, even in China.

[BFL13]

JiminDenver wrote:
My understanding of temperature compensation is that it changes the voltages depending on conditions. Higher voltage for cold, lower for hot. The Eco-W clips amps when it is hot, not voltage. It's too bad too because looking at the one I have opened up on my desk, the sensor is on two small wires and could easily be extended to the batteries.

Any info on how much it clips (reduces would be a better word?) the amps vs the ambient temp where the controller is mounted? I hope it doesn't do that in the shade where it is 25C in the compartment like mine has often been this past summer.

I thought my loss of amps was all about panel temperature and the voltage coefficient. If it is (also) the controller, then what to do? Maybe it needs a thermostat controlled fan like a converter has?

[JiminDenver]

My understanding of temperature compensation is that it changes the voltages depending on conditions. Higher voltage for cold, lower for hot. The Eco-W clips amps when it is hot, not voltage. It's too bad too because looking at the one I have opened up on my desk, the sensor is on two small wires and could easily be extended to the batteries.