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Old 07-20-2019, 08:15 AM   #1
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Charge controller comparisons! Running two controllers

I found a very interesting video on comparing charge controllers. It talks about Mttp vs PWM and the age-old "Can I run two different charge controllers to one battery bank".

The gentleman uses a testbed to compare two controllers at a time with real-time output measurements.

None of his charge controllers interfered with each other during the bulk charge process. He basically calls it a myth. He is testing with a lithium battery which can take in a lot of power before backing off, but I would think that even lead-acid would benefit from two arrays.

Have a look. The "myth" starts at 11:35.

https://youtu.be/kF_cVEYxj3E
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Old 07-20-2019, 08:33 AM   #2
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Hi

Full current full load charging with the battery well below the charger output has never been the issue. The gotcha is the "tail" of the charging process (the last 20% that may take many hours) on lead acid's.

Bob
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Old 07-20-2019, 08:53 AM   #3
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Hi

Full current full load charging with the battery well below the charger output has never been the issue. The gotcha is the "tail" of the charging process (the last 20% that may take many hours) on lead acid's.

Bob
But isn't it true that you may not need both solar arrays to finish the charge cycle? Let me try to explain with my so limited battery knowledge!

If at the end of the cycle, isn't it a much smaller amount of energy that "tops off" the batteries? Like the last 80%. Do you even need both arrays providing power at this stage? And is it true that lithium can accept the higher current (hmmm here is where I get myself into trouble!) for a longer time and benefits with both arrays contributing as the lithium is accepting a bulk charge?
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Old 07-20-2019, 09:02 AM   #4
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Great video. That guy (Will Prowse) has several good how to videos. Thanks.
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Old 07-20-2019, 11:05 AM   #5
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This is our second Season of using solar...I have never gotten back to 100% while camping. Two Zamp 160w panels thru two controllers.
If we can stay above 60% 'til we are back on the pad it's all good. 👍

Bob
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Old 07-20-2019, 11:41 AM   #6
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Originally Posted by ROBERT CROSS View Post
This is our second Season of using solar...I have never gotten back to 100% while camping. Two Zamp 160w panels thru two controllers.
If we can stay above 60% 'til we are back on the pad it's all good. 👍

Bob
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So you are saying you never get out of bulk mode? 60% would still be in bulk.

I have 270 watts and usually recover by midday when there is sun.
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Old 07-20-2019, 03:47 PM   #7
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So you are saying you never get out of bulk mode? 60% would still be in bulk.

I have 270 watts and usually recover by midday when there is sun.
No...60% is the lowest I go before unfolding the suitcase.

I never expected to reach 100% with 360w and 4-6hrs of Sun.
I'm happy with 80-85% with an afternoon of full Sun.
I'll save 100% for on the pad plugged in.

Bob
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Old 07-21-2019, 05:57 AM   #8
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But isn't it true that you may not need both solar arrays to finish the charge cycle? Let me try to explain with my so limited battery knowledge!

If at the end of the cycle, isn't it a much smaller amount of energy that "tops off" the batteries? Like the last 80%. Do you even need both arrays providing power at this stage? And is it true that lithium can accept the higher current (hmmm here is where I get myself into trouble!) for a longer time and benefits with both arrays contributing as the lithium is accepting a bulk charge?
Hi

The point is that for possibly 5 hours you will only have one device doing its thing. Maybe that works, maybe it doesn't work. The current tapers so no it's not 30 to 50A at the tail end. Most of us don't have solar setups that will supply 50A into the batteries. If you are looking at something like 10A, (maybe as 5 + 5) that *is* the taper current ....

The basic math:

200 AH worth of capacity (maybe)
20% of that is 40AH
40 AH for 5 hours is an average rate of 8A

Yes, you will start off higher and end up lower.

Bob
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Old 07-21-2019, 06:17 AM   #9
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Quote:
Originally Posted by ROBERT CROSS View Post
This is our second Season of using solar...I have never gotten back to 100% while camping. Two Zamp 160w panels thru two controllers.
If we can stay above 60% 'til we are back on the pad it's all good. 👍

Bob
🇺🇸
My bad...two 180w🥴
Bob
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Old 07-22-2019, 06:33 AM   #10
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Hi

With 4 panels on the roof and a power hungry electronic control system (and all the WiFi and computer stuff) we run a bit less than 100AH a day on a typical day out camping. If we luck into a site with enough sun, the solar takes care of that on most days. We typically stay in the 70 to 100% range on the batteries. (if there's sun).

Yes, there's a lot of differences. We're running a single controller and it's set up specifically for our batteries. We also run Lithium's. That makes them easier to top off quickly.

Bob
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