Seeking help with controller settings

RussOnTheRoad

Yikes! Now that I have purchased a controller with user programmable settings (Blue Sky Sun Charger 30, PWM) it has dawned on me that the responsibility for picking the best settings has shifted from the shoulders of the manufacturer of my previous controller with no user programmability onto my own!

So, here I sit, happily, but somewhat ignorantly about what the best settings would be for my setup which is 120 watts (2x60 watt PV panels), about 6.7 amps max output, two 12 volt, deep-cycle marine batteries in parallel with what I expect to be about 75 Ah capacity each for a total of 150 Ah capacity at the 20 amp rate of draw. All this in the coach section of my motorhome, separate from the chassis battery (except that running the engine will also charge the coach batteries).

The battery distributor (and manufacturer?), Johnson Controls, gave me some info regarding charging the batteries, but I think they are a little mixed up. Here is the info they gave me about charging and my interpretation of it:

Absorption (Johnson Controls called this Bulk)
14.4-14.8v, 10 amps, time can vary depending on battery condition

Float
12.9-13.1v, 1 amp

Equalization (Johnson Controls called it Absorption)
16-16.3v, 2-4 amps, 3-6 hours

Do my interpretations sound correct?

Next, since I have two 12v batteries in parallel I was thinking of doubling the length of the Absorption cycle from the factory preset of the controller which is 2 hours to four hours. Is that right thinking? I'm in the dark as to what the optimum length of time might be so I'm just basing my choice on that of the manufacturer.

Finally, for whatever reason (I haven't yet figured this out) voltage at my battery terminals is below that measured at the battery output terminals of the controller. The difference in volts varies, sometimes nearly 1.5v, at other times maybe .75v. So, what I'm doing is adjusting the controller to create the desired voltage as measured at the battery terminals rather than what the voltage is at the controller. Here to I'm wondering if I'm thinking right.

Thanks.

BB.

You have most of it down right. For Absorb--2 hours is good for a lightly cycle battery. And 4-6 hours for a deeply cycled lead acid battery. Note, in winter with fewer hours of sun, setting absorb to 6 hours is pretty much just all the energy you can get from the array into the battery bank.

Note that Equalization is an issue. You need to have the battery pretty much charged before equalization "begins". And around 2.5 to 5% of battery bank AH capacity for equalization current (100 AH battery , 2.5. 5 amps or so).

Also, equalization is sort of hard on the battery bank. Some battery mfg. say to equalize once a month, others when needed (when specific gravity is between 0.015 to 0.030 from low to high cell). Note that AGM/GEL/Sealed batteries generally should never be equalized at high voltages (can damage battery).

Get a good Hydrometer to measure / monitor your specific gravity.

-Bill

RussOnTheRoad

BB. wrote: »

You have most of it down right. For Absorb--2 hours is good for a lightly cycle battery. And 4-6 hours for a deeply cycled lead acid battery. Note, in winter with fewer hours of sun, setting absorb to 6 hours is pretty much just all the energy you can get from the array into the battery bank.

Note that Equalization is an issue. You need to have the battery pretty much charged before equalization "begins". And around 2.5 to 5% of battery bank AH capacity for equalization current (100 AH battery , 2.5. 5 amps or so).

Also, equalization is sort of hard on the battery bank. Some battery mfg. say to equalize once a month, others when needed (when specific gravity is between 0.015 to 0.030 from low to high cell). Note that AGM/GEL/Sealed batteries generally should never be equalized at high voltages (can damage battery).

Get a good Hydrometer to measure / monitor your specific gravity.

-Bill

Thanks, Bill. Should I double the absorption time because I have two batteries?

Photowhit

RussOnTheRoad wrote: »

Finally, for whatever reason (I haven't yet figured this out) voltage at my battery terminals is below that measured at the battery output terminals of the controller. The difference in volts varies, sometimes nearly 1.5v, at other times maybe .75v. So, what I'm doing is adjusting the controller to create the desired voltage as measured at the battery terminals rather than what the voltage is at the controller. Here to I'm wondering if I'm thinking right.

Much of this was explained to you in a previous thread. have you considered heavier cables or moving the charge controller closer to the battery bank?

RussOnTheRoad

Photowhit wrote: »

Much of this was explained to you in a previous thread. have you considered heavier cables or moving the charge controller closer to the battery bank?

You are quite right that in regard to the loss of voltage I received some excellent feedback in another thread. I think you misunderstood this post, however. I was not asking about the loss of voltage, but rather inquiring about controller settings in order to compensate for it until I can track down the reason for the voltage loss. Perhaps I could have been more clear.

BB.

The problem is that (every controller I have seen) cannot really be programmed properly to account for voltage drop (there are some controller with remote voltage sense leads which can help address this problem)..

If you program it to give you +0.75 volts at 30 amps, then at 3 amp when you only need 0.075 volt offset, instead, the controller is still pumping ~0.7 volts extra into the battery when finishing the charging. Not really a good idea long term (overcharging batteries).

-Bill

gww1

I may be reading this wrong but I get from the op post that the charge controller is reading higher then the real battery voltage and it is not a voltage drop issue if this is happening with no charging going on, it is a calabration issue. It is a voltage drop issue if it is happening while charging is going on but my opinion is that his settings of getting the cc to charge properly by measuring at the battery is his only real choice. I would look at two other things. Do you trust your multi meter? and Do you reconize that the most important time for this measurement to be correct is at the very end of your absorb cycle when the battery is takeing the fewest amps right before going to flote. If you get this correct it will be the best you can do.
gww

RussOnTheRoad

Thanks for your input.

Let me first reply to your opening remarks where you wrote "...the charge controller is reading higher then the real battery voltage and it is not a voltage drop issue if this is happening with no charging going on". It doesn't happen when in the Charge OFF state, only during the Charge ON state so it appears to be a voltage drop issue rather than a controller calibration problem. In the Charge OFF state the voltage at the controller and battery terminals is the same. This voltage drop has been the subject of another thread I started so discussing it here may be wandering from the reason I started this thread which is to decide how to set my controller to compensate for this disparity until I can figure out why the disparity exists and take action to correct it.

To that end the info you provided about the end of the absorption cycle vis-a-vis taking readings is not something that had occurred to me and is good to know. I will keep an eye on things and try to adjust my controller so that I get the desired reading at the battery terminal at that time. I can set the float voltage separately.

I trust my mulit-meters, BTW. I have two of them, both by Klein. While they aren't Fluke meters I think they are pretty good, and they agree with each other. One is a clamp meter, BTW, that measures both AC and DC amps

I'll endeavor to set my controller so that the voltage measured at my batteries is where I want it when nearing the end of Absorption phase.

Thanks!