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Small Cabin Forum / Off-Grid Living / Need some pointers on new charge controller settings
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# Posted: 22 Jul 2016 17:59

I just got a new charge controller that has a few more features than my old one, such as adjustable High Voltage Disconnection which shuts off the power from the solar panels to the battery when they're fully charged. The default setting is 13.8V...I was wondering if I should leave it there or go a little higher.

I am using (3) 100ah AGM batteries with (2) 150W solar panels with a 1500W inverter. I am not at the cabin everyday. Thanks for your advice.

# Posted: 22 Jul 2016 23:54

You need to get that data from your battery manufacturer. I had to input my Deka battery specs into the Midnight Solar KID charger. Bulk, absorb, float and equalization settings among a few others. Each battery manufacturer will have its own specs.

# Posted: 23 Jul 2016 01:03

Charge Chart

# Posted: 23 Jul 2016 13:32

Note that trojan are a completely different animal from agm.

What are the specs on your batteries from the mfct?

This is the rolls agm charge page.

They specify an "absorb" charge rate of 14.8 for their 12v batteries. And float of 13.9.

So your "max" may be less than the recommended float.

# Posted: 23 Jul 2016 16:27

Quoting: creeky
Note that trojan are a completely different animal from agm.

My Trojan 31 is an AGM.

Quoting: rugercpl
adjustable High Voltage Disconnection which shuts off the power from the solar panels to the battery when they're fully charged.

The charge controller should stop charging when the battery reaches about 12.7-12.8 volts.

The charge rate and the battery charge level are two different things. Overcharging your battery will damage it.

# Posted: 23 Jul 2016 20:14

sorry dave but that is wrong. and not just a little bit erroneous. but ...

1. there is no way for your charge controller to tell if your battery is 12.7. All batteries have resistance. even my lithium batteries. so the reason Rolls (the best of the lead acid breed) says charge with 14.8 is that this is the charge that stuffs electrons into a lead acid battery quickly such that when you leave it alone it for awhile it settles down to fully charged. ie. 12.7.

In summation: 14.8 (for a high quality battery like a Rolls) is what it takes to quickly and efficiently stuff electrons into lead.

If you don't know that. Have a look at battery university dot com.

I'm not being ... what the what what. this is lead acid charging 101.

dave. your charge chart refers to battery voltage as a settled state value. not as a charge value. what I'm saying is:

batteries have a full. a diminished. a discharged. a charge. a lifespan. all kinds of values. and those values cannot be read accurately based on mere voltage measurements at the moment they are taken. sadly.

the trick is to discern what is the value that you need to achieve. based on your need.

So for your Trojan agm 31s. Your solar charger should be set to a value (according to Trojan. not according to me)

Absorption Charge 14.1 14.7

that will put electrons into the lead. (remember. resistance to absorbing energy). 14.1: longer absorb period. 14.7. Shorter absorb period. It's up to you.

Most go to 14.7 as the sun only shines for so long. Hence:

Your solar charger should be set. I would suggest. To 14.7 for a minimum of 180 minutes. This, when your battery, with no load, has a chance to rest, will result in a fully charged value of 12.7.

Trojan states your float value should be (float is your after charging value):

Float Charge 13.5

Again: that's Trojans value. Not mine.

My old Crowns were 14.5 charge (180 and as they aged 210 min). And the float was also 13.5

Float values have many variables which I won't go into here.

Stick to the mfct recommendations for longest life.

If you're using your solar charger to charge to 12.7 and think you're fully charging your battery. Well. Good luck with that.

# Posted: 23 Jul 2016 20:20

ps-typically when someone references trojan they are talking about the 105s.

So thanks for specifying that you have agm 31s.

and of course. when folks outside of the solar world talk about trojans. well.

# Posted: 23 Jul 2016 21:30

and pps.

Dave was right about the "rest voltage."

and for perspective:
I just rewired my first 1kw panel set (4 at 250w) that were 48vx11a to 2 sets of 96v at 5.5a (nominal).

and got bit like hang by mosquitoes. so. you know. it's all good.

# Posted: 25 Jul 2016 11:41 - Edited by: offgridjunkie

Here is the manual. See page 20 of the PDF for AGM battery settings. I use this battery as well and have had good results.

Trojan AGM URL

I watch my batteries while they were charging. Mine CC puts in about 14.5 at bulk and floats it at 13.7 volts. When I put a nice multimeter on it, I got 14.4 bulk and 13.5 Float, so make sure you test the accuracy of the CC.

# Posted: 26 Jul 2016 12:28 - Edited by: groingo

Your charge controller will automatcally adjust based on battery
You can set your battery input perameters to the highest setting
and the charger willw adjust based on battery resistance otherwise
everyone would be blowing their batteries up.
Your instructions should have settings for flooded and AGM so read
those directions.
Personally I set mine at full 15 volts input which gives max amps when
the batteries need it and don' t forget to check you settings if you disconnect
your controller as it will revert to the lower defaults.

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