Your thoughts please / Shunting Controllers..

Maine Sail
Maine Sail Registered Users Posts: 11
This video was taken on a sailboat that resides on a mooring. The alternator usually gets the bank back to about 80-85% state of charge and the solar panel puts the last 15-20% in.

The problem is that sailboats on moorings have no loads or less than 0.2A on the batteries and the cheap charge controller brings the voltage to absorption, in this case 14.2V, and then shuts off. This is a healthy bank of batteries and the surface charge takes time to dissipate.

This particular bank was still down 25Ah's and this is how the controller was performing. It would come on for about 5-6 seconds, the voltage would hit 14.2V and it would then shut off for close to a minute and come back on around 13.5V. It was taking 5-6 days to get from 85% SOC to 100% SOC.

http://www.youtube.com/watch?v=UUaQ2FiEh2Y

I replaced this Flex Charge PV7 with a Genasun GV-10 MPPT and the batteries are now back to full in just two days vs. 5-6 days. I don't attribute this to the MPPT at all and find it's that the Genasun does not do the same on/off behavior the Flex Charge does.

Is this how these shunting controllers are supposed to work? It takes forever to get the last 10% back into the bank. Is that normal? I have also seen this, only worse, with some of the cheap Sunforce controllers that shut off at 14.2 and don't come on until 12.9V. I had one boat with an AGM bank that would sit at 13.0V for well over an hour before the controller would come on for a few seconds and shut off again for another hour..

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Your thoughts please / Shunting Controllers..

    There's a few factors at work here.

    First of all, that's the way batteries charge. The last bit takes much longer per Amp hour gained than the first. This is all to do with the Peukart effect. It doesn't matter what batteries/panels/controller you have, this will come in to play.

    Second, el cheapo shunt controllers aren't really charge controllers; they're Voltage regulators. They turn off at a high Voltage set point and back on at a lower one. This is no way to charge a battery, especially not a deep cycle.

    A "real" charge controller will bring the battery Voltage up to the Absorb set point (usually 14.4 on a "12 Volt" system with FLA's) and hold it there until the charge is complete (the method of determining this varies). Then it drops back and maintains Float Voltage for as long as it can. PWM type controllers still switch on and off, but very rapidly so there is effectively no "range of Voltage".

    A third potential contributing factor is low Vmp panels. The greater the difference between the charge Voltage and the battery Voltage the greater the current flow and the faster the charge rate, even in the final low current stage. If the panel Vmp is 16 instead of the typical 17-18 this can prolong the final charge stage.

    Sorry if this is overly simple; writing for the benefit of anyone who might be wondering about the same situation.
  • Maine Sail
    Maine Sail Registered Users Posts: 11
    Re: Your thoughts please / Shunting Controllers..
    There's a few factors at work here.

    First of all, that's the way batteries charge. The last bit takes much longer per Amp hour gained than the first. This is all to do with the Peukart effect. It doesn't matter what batteries/panels/controller you have, this will come in to play.

    Very well aware of acceptance issues as e have to deal with them on boats too..
    Second, el cheapo shunt controllers aren't really charge controllers; they're Voltage regulators. They turn off at a high Voltage set point and back on at a lower one. This is no way to charge a battery, especially not a deep cycle.

    All charge controllers I suspect are voltage regulators as I don't know of any that have a shunt to know the current? They all control the voltage, and resulting current, slightly differently but they all "limit" voltage.. I just find it horrifying that people pay good money for these shunting regulators vs. a PWM or MPPT as they kill your charging speed when you get close to full..
    A "real" charge controller will bring the battery Voltage up to the Absorb set point (usually 14.4 on a "12 Volt" system with FLA's) and hold it there until the charge is complete (the method of determining this varies). Then it drops back and maintains Float Voltage for as long as it can. PWM type controllers still switch on and off, but very rapidly so there is effectively no "range of Voltage".

    Even MPPT controllers I have installed, Blue Sky, Morningstar & Genasun cycle on/off but not until the batteries are full and when they do go off/on the duration is usually less than a second or two in the OFF position...
    A third potential contributing factor is low Vmp panels. The greater the difference between the charge Voltage and the battery Voltage the greater the current flow and the faster the charge rate, even in the final low current stage. If the panel Vmp is 16 instead of the typical 17-18 this can prolong the final charge stage.

    Vmp is not the issue as when the controller was changed from the Flex Charge to Genasun the "top up" time dropped from 5-6 days to 2 days. Same panel, same wiring, same battery bank...

    To be sure of my test results I charged the bank to full via the vessels shore charger then re-set the battery monitor. I then removed 15% of the banks capacity or 30 Ah's from a 200 Ah bank and let the controller charge it up. With the 80W panel & Flex Charge this, over three rounds, took 5-6 days to replace the Ah's removed. With the Genasun the same Ah's were replaced by day two even with some clouding. I repeated the test three times with the Flex Charge and two times with the Genasun. The owner has since reported that the bank is consistently reading full by Tuesday afternoon with the Genasun and with the Flex Charge it was sometimes still down 8-10 Ah's on Friday when they arrived for the weekend.
    Sorry if this is overly simple; writing for the benefit of anyone who might be wondering about the same situation.

    Not a problem at all, overly simple is good!
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Your thoughts please / Shunting Controllers..
    Maine Sail wrote: »

    Even MPPT controllers I have installed, Blue Sky, Morningstar & Genasun cycle on/off but not until the batteries are full and when they do go off/on the duration is usually less than a second or two in the OFF position...
    I just find it horrifying that people pay good money for these shunting regulators vs. a PWM or MPPT as they kill your charging speed when you get close to full..

    I know nothing about the Blue Sky, or the Genasun, but I've owned and used three Morningstar controllers, one PWM, the other 2 MPPT, as well as an Out Back MX-60, and all 4 of them in normal operational settup, do not switch on and off as such, rather they control the current flow as required, through Pulse Width Modulation at a very high rate of speed, the result of which is a gradual reduction in current, all the way to zero if necessary, to control the charge.
    As to shunting regulators killing charging speed near end of charge - - not if they're of the PWM type.
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Your thoughts please / Shunting Controllers..

    The Flex Charge shunt controllers are not a particularly good solar charge controller. Shunt controllers in general pretty much went out of the picture some 10 years or so ago. For a non-MPPT controller the Morningstar are much better, especially in the "top off" algorithm.

    In addition, your changing from a "not that great" shunt controller to an MPPT controller would give you an extra 10-25% charging amps just by itself.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Your thoughts please / Shunting Controllers..

    When in a circuit, the "on/off" function of a PWM or MPPT charge controller is not noticeable. Id est: you can put a Volt meter on the battery and you will not see any change in Voltage between the time when the controller pulses "on" and when it turns "off". There will simply be a steady increase in Voltage over time until the next set point is reached (providing input from panels is consistent and there are no loads drawing from the battery).

    A good charge controller is worth the money. A bad one isn't. ;)
  • Saggys
    Saggys Solar Expert Posts: 189 ✭✭✭

    Turn up the voltage shut down set point on the flex charge and repeat test.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin

    The original post was 8 years ago, and the poster has not been back for 6 years...

    We really do not need to bring this thread back to life.

    -Bill "moderator" B.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Saggys
    Saggys Solar Expert Posts: 189 ✭✭✭

    Sorry, I did a search on this subject and came across it. I have some interest in the subject because of its simplicity. I will refrain in the future from commenting on old posts.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin

    Not a big deal.

    The post was written as if a response may happen from the original poster and to repeat the test.

    In this case, probably not.

    Posting additional information (i.e., I had a similar problem and changing....) Is always good to have.

    We have had a few zombie threads on the past, and they tended to wander.

    Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset