Battery voltage sensor placement TrisStar 45 MPPT

[Rover]

So yesterday I put in my new TS 45 MPPT. All wired correctly. Powered it up and t appeared to be working just fine(there was no sun at the time)
System details (12V battery bank 6 GC2 batteries, 200W solar on this controller (going up to more shortly))

The TS  has a battery voltage sense option,  that allows you to connect a small pair of wires to the battery bank to improve accuracy over the built in voltage sensor. I had added this and 18g wires that went to 2 battery terminals.

At power up, the TS voltage, matched my meters, and my monitoring system, all is good.

Later on in the day, when the panels were in full sun, I look at my monitoring system, and the voltage is at 15.5, so I go look at the TS thinking its trying to equalize or I have set the wrong parameters for the battery. It reads 14.8 V. Huh? , a .7 Volt difference from the meters and monitoring system. I know the meters are correct. The TS must be reading wrong.

Then I work it out, I had placed my voltage sense contacts on the same posts as solar input lines from the TS where current was flowing, that was creating a voltage drop on the voltage sense lines.

Today I moved the voltage sense contacts to unused posts on the battery bank. Now everything is reading the same . Moral... watch where you put the voltage sense contacts. In this case if I hadn't rectified the problem I would have been continually charging at a higher voltage than spec, probably not a good thing.

Rover

[oztules]

Glad it works..... but I don't quite understand.

When you mentioned the .7v I figured a diode in series somewhere.......  but not that.... so:

I would have thought that putting the sense lines on  the input posts would have given you the opposite effect..... ie it would be at the highest EMF of any part of the bank when charging.... wondering why you found it to be the lowest by .7v....

Does not compute in my tiny mind.

I would have thought that the input posts would give you an artificially high reading in charge mode.... not the opposite.


...............oztules

[Rover]

It didn't make sense to me either, and I never cosidered the possibility of something like that when placing my voltage sense wires. So of course I dug through the TrisStar manual (which is a good manual). 

And although the section I read, related to why you should use the separate voltage sense as opposed to the onboard, was that any current carrying wire will cause a voltage drop. So if you used the onboard (sensing from the controller output) there would be a voltage drop.

Maybe, what I did was not related at all, maybe it was just moving the sense wires, maybe better contact , etc. But I find that unsual if so as tehy were clamped down the same way on the binding posts.


From the manual
"Voltage drops are unavoidable in power cables that carry current, including the TriStar MPPT
battery cables. If Battery Sense wires are not used, the controller must use the voltage reading
at the battery power terminals for regulation. Due to voltage drops in the battery cables, the battery
power connection voltage will be higher than the actual battery bank voltage while charging
the battery.
Two sense wires, sized from 1.0 to 0.25 mm2 (16 to 24 AWG), can be used for battery voltage
sense. Because these wires carry no current, the voltage at the TriStar will be identical to the
battery voltage. A 2-position terminal is used for the battery sense connection"

It is is quite possible that I have misinterpreted the whole thing.

[ghurd]

0.7V is a lot.  Guessing a bad connection somewhere.

Was there a load on the system?
Charging current goes one way.
Load current goes the other way.
Combined, the result could be either way.

The sense wire battery terminals are soldered, and the sense wire itself is soldered solid where it screws into the TS45, right?

It doesn't take much to throw if off a tad.
In the ghurd controller, the Yellow LED (dump load is dumping indicator) current (3 ~ 3.3ma) causes enough voltage change in the sensor wires that it had to be included in the design calculatons.
G-

[Rover]

Hi Ghurd,

At the time there was no load on the system. Charge current was probably around 10A.

The sense wires are nothing more than 18g wires with crimped on ring terminals to the battery posts, on ts 45 the wires go into screw terminals.

Funny thing is that now that meters all jive, really not worried about, it could be a bad connection or what not, but it was funny that only when the TS 45 was charging was there a difference.

Now I'm just worknig out how to get the TS 45 to play nice with the Blue Sky... (actually it may be playing nice just seeing behavior I'm not used to)
 

[ghurd]

I have not used a lot of Blue Sky stuff.
They are not temp compensated.

Might have to set the TS45 to a slightly higher voltage.

Probably be a very good idea to keep the Blue Sky power wires, and TS45 power wires, completely separate, except for at the battery terminals.
G-

[Rover]

Hy G,

I'm just getting used to it , I two arrays spread from each other, one is the "early" array 330 W plugged into the blue sky, the other is a "later  array"  200W going in to the TS 45. (early / later refer to part of the day when the arrays get sun, these are fixed).

Looking at my curves it makes sense now, after reviewing the absorption points, for the blue sky its  14.2 for the ts 45 I have it set at 14.6 (preset #5) . Temp has been low as well, so when the sun starts to hit the 2nd array the TS starts pushing the voltage up and the blue sky basically starts to shut down. All of this is expected, the temp compensation on the TS does really work as it will go to ~ 15V in 40-45F.

Its unusual for me as my Bz used to control the 2nd array , and had a lower set point than the Blue Sky .. so the blue Sky array would win out.

(For anyone else, the blue sky and the BZ have factory set absorption set points, the TS does not , but without reprogramming you have to choose one of the presets)

In any case the bank has been at 90% SOC before charging so the effect of getting into absorption is pretty quick (hour or so) . When I start using the bank more and the daily SOC falls, this will all be less of an issue

Other words, no real concerns.

Rover...

[ChrisOlson]

Rover,

Does your TS MPPT seem to be getting your panels to all they can put out?  I got a TS MPPT 60 on my Sharp 123's wired for 109.0 Voc and it rarely reaches full rated power of the panels even on a good day.  And it's been terrible on cloudy days.

I got two TS's - a 45 on my Schott array and a 60 on my Sharp array.  There has been days when I've been able to see the orb of the sun thru the overcast, when I figure I should be getting at least 30% from the panels, and they barely make 20%.  I'm pretty sure I used to get more from the Sharp 123's when I had them direct-hooked on 12 volt.  There was many days in the winter when the sun would peek out for a bit and I would see them hit 80 amps @ 14.5 volts.  With the TriStar controller on them (now 24 volt) I've seen 38 amps only a couple times.

So I dunno, but I can't really say I've been exceedingly happy with their performance. 
--
Chris

[rossw]

There has been days when I've been able to see the orb of the sun thru the overcast, when I figure I should be getting at least 30% from the panels, and they barely make 20%.

The eye is a truly terrible estimator of light intensity.
A cheap lightmeter is a help, but a pyranometer is the proper instrument for the job.

Ever since I installed mine, I've been *far* better equipped to compare output achieved with what I'd "expect".
It's surprising how much difference a high-humidity day, or day with moderate amount of smoke for example, makes to solar output.

[Rover]

Chris,

All I can really say is that it does better than BX MPPT did. Although this is all relative and I only have 2 100's on the ST 45 MPPT right now, (that will increase 2 4 shortly) and the panels are wired parallel.

Ask me in a month or so, after I get a few more panels on line and change to a series parallel configuration.

Rover

[Rover]

I should probably add that I will very likely never see the rated capacity of the panels as it feeds a battery bank which I don't discharge more than 30% on average. Also since these panels get sun after my other set, there already has been charge going to bat when these go active.

Rover

[ChrisOlson]

What's BX MPPT?

Ask me in a month or so, after I get a few more panels on line and change to a series parallel configuration.

What I'm considering doing it putting a Classic on my Sharp 123's to test it.  I bought another Classic 150 controller because I'm going to put it on another wind turbine.  If I get more power from the panels with the Classic on it, I will probably re-wire my Sharp 123's for 218.0 Voc and get a Classic 250 for them.  In that case I'll have a used MPPT 60 for sale.

There's some other things I like about the Classic - one being it has HyperVOC so wiring the panels up near the voltage limit of the controller won't hurt the controller on really cold days.  The other being it can melt the snow or ice off the panels, which for me is a main thing here.
--
Chris

[Rover]

Hi Chris,

Assuming you feed to bats, what is the SOC of the bank when the panels come on. Quite honestly if you are doing so well with wind and acknowledge a bad solar area, isn't it pretty much to be expected?

I have the reverse... crappy wind and mediocre solar, but my solar has a 20X gain over my wind. Do I still put up mills , yep, cause its a hobby and I'm a nut job.

Rover

[ChrisOlson]

Assuming you feed to bats, what is the SOC of the bank when the panels come on. Quite honestly if you are doing so well with wind and acknowledge a bad solar area, isn't it pretty much to be expected?

Usually they're from 50-80% SOC - it depends.  The bank is rarely below 24.0.

The solar actually works good here in the spring, summer and fall.  I just don't think I'm getting what I should get on overcast days during the winter.  I don't know if there's a way to measure how much solar power is getting thru the cloud deck.  But some days I can see the bright circle of the sun thru the overcast - like looking at the sun thru a welding helmet, and the panels are still only putting about 20%.  Most guys claim I should be getting more than that.

When the sun actually peeks thru so it's shining direct on the panels and it's really cold out, they will get to rated power.  But isn't the idea of MPPT to get more power from the panels under less than perfect conditions?

Frankly, I don't think I'm getting any more with MPPT on them than if they were direct hooked.  That's why I want to try a different controller.
--
Chris

[Rover]

Chris,

Don't think there is an easy answer here. In order to come up with a conclusion you will need to data log your sources over a large period of time (large enough that you can average out and hope you have a decent best day / worst day comparison) . Then you have the successful wind power ...  In order to evaluate the performance of the solar panels you would need to isolate them as the sole charging source.

Way too many variables to define how your solar is doing. Course covered in snow is never ideal

Rover