Hello All! Tristar vs. MPPT?

System

Hi all! Great forum and great guys here!

I'm designing a system for my RV.

2 Panels max, maybe 135 watts each.
2 6 VDC GC T-105 batts, wired in series.

10' max run from panels to combiner box, 15' from combiner to controller. 6' to batteries.

Panels will be mounted flat most of the time. Most expected weather is 50-90* F ambient, some shading expected at sun rise and set. Minimum 4 hours direct sun. No winter conditions.

In a real world situation, would you get the Morningstar MPPT controller or the Tristar 45?

I'm (almost) convinced that the most important factor in real world performance is the absorption phase of the charging cycle. I "think" 14.8 VDC is optimum (temp compensated), for a minimum (more is better with these batts), 1 hour. I'm thinking the DC to DC conversion of the MPPT controller, accounting for loses, won't exceed the harvest of the Tristar at this setting.

Besides the obvious head room problem, am I forgetting anything?

(a recommendation on optimum wire size would be very helpful. I have a crimping tool and can use welding cable).

Thanks for any help!

System2

Re: Hello All! Tristar vs. MPPT?

bodfish wrote: »

I'm thinking the DC to DC conversion of the MPPT controller, accounting for loses, won't exceed the harvest of the Tristar at this setting.

I've used (it's sitting on a shelf now) a Tristar TS-60, but shifted over to an MX-60 and would never go back. That said, I live in an area with real winter and the cold temps that go with it, allowing the MX to make use of the higher winter PV voltages.
In your area with year round warm temps, you may well be right.
One advantage of the MX over the Tristar, is the many user adjustable parameters, giving you much finer control of things, than with the TS.
The TS has only limited adjustments in that area. One thing I did not like about the TS, was the way it determined when to switch over to FLOAT. It monitors the PWM of current going to the batteries, and that PWM must register I think it was only 20% of the max, for several hours before the switchover will take place. Seems it was designed to function properly with a PV size matched to the battery size, and if you're outside that range, it won't work right. Another thing, if you have any intermittent load, such as a fridge, every time the fridge goes, it disturbs the PWM % and resets the time needed before switchover to FLOAT. In 2 years, I only ever saw mine go into float half a doz times. In the meantime, I feel lucky that I had flooded batteries, as they handled this abuse better than I understand other types will.
The MX-60, monitors voltage and time as the reference for when to transition to FLOAT, regardless of the loads on the system. I'm very happy with that, am able to run both fridge and freezer, and as long as the battery voltage stays up where it should be for the required time - - BINGO, FLOAT!
So keep that in mind too, as you make your decision.
Best regards
Wayne

System2

Re: Hello All! Tristar vs. MPPT?

Regarding your panels mounted flat most of the time, are you able to get at them esily to clean them off? Or do you have regular rains to wash then off? Dirt buildup will greatly reduce their output.
Also, you mentioned shading. Be aware, that these panels are much like the old Christmas lights that were wired in series, in that if one goes out, they all go out. Likewise, shade any part of one panel and BOING goes your output from that panel. AND, if you wire them in series, BOING goes the output from BOTH panels.
Cheers and good luck, I hope this has helped.
Wayne

Solar Guppy

Re: Hello All! Tristar vs. MPPT?

No question, the MorningStar Sunsaver Mppt ... Its a good match for your panels and will out havest the Tristar for sure. The MX-60 for this power range will consume more power ( tar loss ) than it would increase harvest with its Mppt features, the SunSaver tar loss is less than 400 milliwatts. Your application was the target market for the Sunsaver Mppt

System2

Re: Hello All! Tristar vs. MPPT?

Wayne from NS Cana wrote: »

- BINGO, FLOAT!
So keep that in mind too, as you make your decision.
Best regards
Wayne

Thanks, Wayne..........very interesting. Yet another ingredient to add to the mix, heh?

I never thought of the problems of float while using a load, especially unpredictable ones. I'm wondering whether using the bank continuously would ever allow the batteries to be fully charged?? And to equalize? Have to factor in the limits on any sensitive circuits, too..

But still, my opinion is that the last 15% of capacity is never achieved due to the algorithm (on most controllers) switching to float much too soon.. The Trojan Company advises 14.8 V, at the batteries for a minimum of 1 hour, and more is better to a point. Most won't even allow 14.8 VDC at all.

Why is this important? Well, for a small system wasting the top 15% of capacity is really about 30% when you recognize that the higher voltage equals more watts in that top area. And this may save a panel..

Naturally this is for deep cycle flooded.

Solar Guppy

Re: Hello All! Tristar vs. MPPT?

The SunSaver Mppt can be programed for custome values on all the charging state transistion points ( voltage ) and it automatically transistions back to absorb if in float when a load pulls the voltage down

System2

Re: Hello All! Tristar vs. MPPT?

Solar Guppy wrote: »

The SunSaver Mppt can be programed for custome values on all the charging state transistion points ( voltage ) and it automatically transistions back to absorb if in float when a load pulls the voltage down

Ok, thanks a lot!

So, I assume you would wire the panels in series? Or maybe one big 24V panel?

If I can program the SunSaver to my specs, then I think you all are right!

Say 10 GA to the combiner, and #2 to the controller and to the batts?

BB.

Re: Hello All! Tristar vs. MPPT?

The MorningStar MPPT manual is here.

Don't over size the wiring--just follow the manual's recommendations. Also, if you have a choice, keep the controller to battery wiring as short and heavy as practical. The control needs to monitor the battery's voltage accurately--and too long and small of wire can cause the battery to not charge as well as desired.

-Bill

They also have a solar panel array string calculator too (doesn't work for me on FireFox?).

System2

Re: Hello All! Tristar vs. MPPT?

BB. wrote: »

The MorningStar MPPT manual is here.

Well the 15V max allowed charge voltage is a deal breaker for me.

Charging at 14.8 V, I wonder what the voltage should be when, say at, 40* F?
I just don't understand these specs, guys. WHY do all the makers think we all use AGM batteries? This would be fine for them. But not for Deep Cycle flooded.

I really mean it.....getting the top 15% charge in a small bank is crtical.
Most guys NEVER get a full charge and waste tons of money on batteries, un-needed panels, higher priced controllers, you name it.

Solar Guppy

Re: Hello All! Tristar vs. MPPT?

Those values are the DEFAULT values, you can program what ever you like to the unit including changing the 15V value.

From the Sunsaver Modbus doc:

ETb_max
[57375][0xE01E](C) Maximum temperature compensation limit
Maximum temperature to clamp temperature compensation.

EV_hvd
[57372][0xE01B] High Voltage Disconnect @ 25ºC
Flag a fault/alarm if the battery voltage exceeds this setpoint. Also attempts to open the MOSFETs to
stop charging. Set to zero to disable HVD


MorningStar ships units with values that keep novice users out of harms way, the 15V value is to prevent electronics connected to the battery from being damaged when a battery compenstated for tempatures would call for a higher value. Its all programable for the end-user to tailor to their needs