Solar and Shore Power Charger not playing well together.

[Scalf77]

The topic has come up before about the combination of multiple charging devices and what the affect would be on your charging system. The easy assumption would be that adding additional charge would be a accumulative affect and thus a positive. As with many complex things the answer is not always easy or simple. The following was an issue I found with solar and my shore power charger working together. The solar charger is question is Morningstar TS-MPPT-45 and the Shore Power Charger the standard Tripp-lite inverter/charger that Sportsmobile installed in 2004. I don’t particularly believe either of the devices is wrong or bad, this is the kind of thing that can happen when mixing things together.
I noticed this when I was updating my RV Status program http://www.sportsmobileforum.com/vie...ilit=RV+status to add more features, and particularly in this case I wanted to monitor the power usage of my existing Norcold refrigerator as I had plans to upgrade to a larger unit.





This Data is very raw, so it looks like it bounces around a lot, but for the purpose of this discussion it is workable. I have since added some smoothing algorithms to the data collection. The samples are taken every 10 seconds. In the following spread sheet you can see the yellow area as the fridge amps, the solar panel is at 16.3 volts with negligible current production, so the solar charger is not really putting anything out. The 0.05 reading would be in its level of accuracy. The inverter amps refers to the Tripp lite charger. You can see an increase in current provided go along with the increase from the fridge. Take note that the House Battery Voltage is a Float level of 13.51 volts, you will see some current from the charger because the sensors are active and also the data collection computer. So far nothing out of the ordinary sticks out.



The next collection of data is interesting and starts to show the two units competing for ownership.. After the fridge cycle ends we start to see some current come out of solar, we also see a drop in current from the Inverter (charger), and still the house battery voltage holds at float level, which is what we expect.



Now on the next sheet we can see that the inverter is still supplying some current for when the fridge comes on, but it will go to zero after that then we see the voltage jump, I think now the solar charger has gone to absorption mode. Interestingly as soon as the inverter is needed to meet the fridge demand the voltage is driven back to the 13.5 float level.




This bouncing of voltage levels continues for about a hour and forty minutes. When the fridge cycles on the inverter drives the voltage to the inverter float voltage. Finally the solar power wins out and now has enough power that the invert is not needed. It goes into absorption mode and stays there.



I have about a two hour window of the solar charger being in absorption mode, with the high voltage output. It is difficult to say if the change to float voltage was caused by a drop in solar charger output, as its current output dropped for a couple of minutes., but we are now back to float voltage,


And then we finally see the solar charger take command and staysat the proper float voltage.




In all a had a three to four hour window where I had the float voltage to high, overtime this could take its toll on my battery. Normally when I leave the van parked in the drive way for any length of time I disconnect the solar and this would not have been an issue.

I will say that this problem has been know to happen on some single charging units, no solar involved. I did go out of my way to look for that in years past and never saw it just using the tripp-lite

Once I finish my refrigerator install, I may look at some data where the battery should be in bulk charge mode, it would be interesting if I see a accumulative effect on the charge rate, this of course could be good or bad, if you have your charger set at a high charge rate, you probably do not want to add the addition rate of solar to that equation.



-greg

[daveb]

Interesting to say the least.
Kind of off topic but I very rarely set my inverter to charge while on the carport. The way I figure it is the solar handles most of it during the day and being there is basically no load (fridge is running off AC power) I'm just using the solar to keep the batteries at float. My inverter also acts as a a low voltage power supply which keeps the separator closed at night. However I've always wondered what that does when the solar is active. When its not and the inverter is set to a no state charge, I've noticed the battery voltage drops from a float voltage to about 12.9-13 volts before the sun comes up. This has always bothered me wondering if the swing from float to what is considered a full state of charge cycles the battery. In the past I thought if an AGM battery can sit on a shelf for a month at 12.8 without damage to it, I was fine on what I'm doing.

Unfortunately I can't monitor like you do Greg, but what you're seeing is interesting. Similar to what I do, I have friends who try to stay off grid as much as possible & they have chargers that run off the utility to keep the batteries up during poor weather. I THINK they also share charging. I'll have to take a closer look.