Controllers alternating?

zozomike · January 2015

Hi, we have had two weeks of foggy weather, ( which freezes on everything) and off and on snow. I have used the generator several times. Today we got some sun around 10:30 and thinking I needed to boost the battery, ( SP barely 1.25 and cells unequal) So I put both controllers on equalize, Oddly only one would charge at a time, one went to sleep when the other was above 1 KW. I could shut one down, the other would wake up. Now it is cloudy again and both are charging in the 500 watt range. I know in the past both have been able to produce fully and simultaneously. Seems there is a threshold around 1.5 kw? What could be going on?

Cariboocoot · January 2015

Re: Controllers alternating?

Why would you put them on Equalize? The batteries need to be recharged before this can be done.
In effect you just set the controllers to trying to raise the Voltage above EQ level and one was affected by the other causing it to think it was done.

Always recharge normally before trying an equalization charge.

Vic · January 2015

Re: Controllers alternating?

mike,

Generally multiple MPPT CCs will all contribute all the PV power that they have in Bulk. Then when a voltage regulating stage, like Absorb or EQ is reached, it can be difficult to have each charge source contribute fairly equally.

Slightly changing the Absorb or EQ voltage on one, will help, but what will allow good sharing on a particular week, may change in the next week.

Sometimes, having a PV array on one CC larger than the array on the/an other CC, you might be able to make the larger-arrayed CC the Leader, with slightly higher Absorb/EQ voltage. This might help, although, have tried this with a two thirds/one third ratio ... your arrays are fairly similar in size.

Have not found a good solution. The MidNite Classics DO have a FollowMe capability, where multiple Classics will follow into the same charge stage, but they still do not necessarily contribute up to the maximum capability of each of their own PV arrays.

There is a lot of variability, including any possible difference in perceived battery temps etc (although, the OB system can share a single RTS, if suitably configured).

Even when you manage to get good sharing in most of Absorb or EQ, one CC may feel that it is time to go to Float, and the remaining CC does not have enough PV power to maintain Vabs, and it falls back to Bulk, and do on. Lotsa variables that are too variable.

FWIW, Vic

zozomike · January 2015

Re: Controllers alternating?

Wow, you guys are fast! I guess I put them on equalize because the Trimetric said we were at 98% full. Should not have trusted that. Did not check the SP until after and was unhappy.... Situation is complicated by the fact that it tried to live without me for the last 7 months while I was out of state working. Guess I'm lucky to have anything working. Thanks for the advice.

BB. · January 2015

Re: Controllers alternating?

If each charge controller is on its own branch circuit back to the battery bank (through its own breaker/circuit breaker).

And you have checked the voltage at the battery bus and at each Vbatt terminal on each charge controller (should be pretty close to the same. For a 48 volt battery bank, I would suggest that you should see a maximum voltage drop/rise of ~0.2 to 0.4 volts on a 48 volt battery bus).

What is the battery charging voltage? If it takes 1,000 Watts to hold 58.0 volts (or whatever your set point is)--Then it really does not matter if one controller does 1,000 watts and the other is 0 watts, or both are at 500 Watts.

-Bill

mike95490 · January 2015

Re: Controllers alternating?

I use 2 different charge controllers, and found that with the remote app, I can easily fine tune the voltages on the Midnight Classic, so that it tracks and shares power well with the morningstar controller, which is more awkward to program.

Vic · January 2015

Re: Controllers alternating?

Getting differing CCs to share Absorb is not too difficult, generally, especially for a given Inverter loading. But having CCs continuing sharing fairly equally can change when a larger load, like A/C starts ... this can change the balance, or even cause one CC to give up.

If an MX-60 CC is in the mix, if it ever sees the battery voltage pulled very much at all above its Vabs (or Veq), it quits charging at all, and will be in Float when the battery voltage descends to Vfloat. So after the point where the other charge sources' voltage decreases to/below the MX's Vabs (or EQ), it will be useless in contributing to charging the battery for the rest of that solar day.

It is easy to set things for a given situation of PV power and AC loads on inverters, but if that changes much, things can become upset. Different CCs behave differently. Am not familiar with just how the FM CCs behave in the above scenario.

FWIW, YMMV, Vic

gww1 · January 2015

Re: Controllers alternating?

I have an fm80 and a mx60 and both have there own little quirks. The mx60 has a lot more quirks that are easy to reconize. When you start adding ssr to run loads from one of the auxilary off one cc the quirks become even more pronounce. I say the mx60 has more quirks you can see but with the exact size aray on each it also produces a bit more power. Both of these cc have a voltage calibration setting. This setting can be used to get them closer to seeing the same thing from the battery and can also be mulipulated with your normal settings to get the cc to work better together.

I have not seen what vic has seen with the mx60 just stopping for the day but did have the fm80 freeze one time and have to be restarted with one of the buttons that makes that comand. I have seen the controllers seem to fight. I have seen the mx hit absorb (it hits absorb first meaning the fm80 take a smidgin more to reach absorb) And then start reducing the voltage even though it is dropping way below the absorb voltage. It will do this till "new voc" pops on the monitor then will go to zero and then start producing again.

It will do this quite a few times like it is learning till finally it will start going up and down as it should and hold absorb. In eq the other day it kept cycleing to new voc. The fm80 with the aux. hooked to it will also show production cycleing up and down but does not zero out for a bit like the mx does. when the load kicks on through the fm80 it is slower then the voltage climb and makes the mx do its mini cycles even longer. In the end however they both always seem to level out and go into absorb for the same amount of time except rare occasions when the mx might finnish first. I Can't believe the little bit of fighting that goes on between them and believe it causes a tiny bit of production loss however in the end they level out and the batteries get charged at the proper settings. When it is windy and the turbines hooked strait to the batteries send power the cc adjust down and up really well to hold the absorb voltage. If I could I would fix some of the quirks but have to say even with the quirks the two cc work really well with each other. It did take lots of Hours of observation to get the settings correct and my confadence that they were correct.
Gww

zozomike · January 2015

Re: Controllers alternating?

Thanks everyone for the input. Bill's point well taken, why worry about it. We have plenty of other real problems.

Controllers alternating?

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