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Old 12-03-2014, 19:15   #151
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Re: MPPT Charge Controller for LifePO4 Batteries

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No issue designing a SEPIC mppt to handle the low voltages can't see why someone hasn't din it
There are a couple of MPPT controllers that will boost voltage (Ganasun make one). They are designed for using 6v panels with a 12v system, or 12v panels with a 24v system.

For 12v (nominal) panels with 12v batteries there is no advantage in low light. There could be an advantage with isolated shadowing if the circuitry could be designed to be as efficient in the normal voltage reduction mode.
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Old 12-03-2014, 19:34   #152
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Re: MPPT Charge Controller for LifePO4 Batteries

Lessee, a keel cooled refrigeration system cooling the back sides of the panels...running on the panels, a net plus??
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Old 12-03-2014, 19:49   #153
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Re: MPPT Charge Controller for LifePO4 Batteries

I have sometimes thought using the underside of the solar panels to heat up fresh water for showering could be made to work. It is hard to gain much improvement in solar output even a 25c reduction in temperature would only produce a 12% improvement and the pump would consume some power, but by running the water during the peak solar times you could certainly heat up your shower water and as a side benefit slightly cool the solar panels.

The important take home message is some air flow under the panels is worth considering.
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Old 12-03-2014, 20:04   #154
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Re: MPPT Charge Controller for LifePO4 Batteries

At the moment, I'm not near my solar arrays, they are each on top of an RV. However, on a nice sunny day, I'll take pics of the solar panel temps from my IR thermometer, then pics of the inout and output voltage based on the MPPT controller and a calibrated DMM, input and output current based on the MPPT display, and compare them to the published Vmp and Imp of the solar panels installed.

About 6 mos ago I installed a very cheap 20A MPPT controller with 2 x 205w Sharp panels. Right after I installed them, I played around with the display a lot during peak hours and put a pretty good load on it to see just how far it would go or if it would damage it. I was pleasantly surprised at the output power and input and output voltages, I don't recall ever seeing panel voltage any more than 1 or 2v lower than advertised, but I'll take pics next time just to make sure I wasn't hallucinating. I'm sure I would have noticed if input voltage and current or output voltage and current had varied much from what I was expecting.
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Old 12-03-2014, 20:23   #155
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Re: MPPT Charge Controller for LifePO4 Batteries

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I wasn't hallucinating. I'm sure I would have noticed if input voltage and current or output voltage and current had varied much from what I was expecting.
A lot of MPPT show input and output figures enabling the MPPT to be readily seen, but unfortunately they are a little deceptive (at least all the ones I have measured). They exaggerate the output current and display a slightly lower input current so that the gain from the MPPT conversion is exaggerated.

All meters have some error, but there seems to be quite deliberate (but understandable) desire to err on the side of emphasising the improvement from the MPPT conversion.

The voltages are usually reasonably accurate and on my display agree with expected Vmp's of typically 15-16.5v, but I would measure them with external meter before you draw too many conclusions.
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Old 12-03-2014, 20:32   #156
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Re: MPPT Charge Controller for LifePO4 Batteries

I have meters I can use to measure voltage and current, I'll check and see just how far off these MPPT controllers are. One is a Blue Sky SB2000e and the other is a cheap $100 Chinese controller. It looks surprisingly well made for the price, and it's fully adjustable via push button menus.

I won't be able to do it for a few weeks, but I'll be sure to post back in here when I do.
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Old 12-03-2014, 23:08   #157
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Re: MPPT Charge Controller for LifePO4 Batteries

Can you please tell us which cheap Chinese controller you used?
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Old 12-03-2014, 23:52   #158
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Re: MPPT Charge Controller for LifePO4 Batteries

For those that have not seen this sort of display before this is a result from my MPPT controller in typical conditions near the middle of the day

The 330w of panels I have are actually producing 310w.

The input voltage (or Vmp less wire losses if the controller is doing its job) is 15.8v. The output voltage is 14.0v (battery voltage plus wire losses). The voltage conversion is raising the input current from 19.6 A to 22.0A.

As I have mentioned the display is fibbing slightly on current, but my display becomes reasonably accurate around 20A so this is not far off reality.
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Old 13-03-2014, 00:11   #159
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Re: MPPT Charge Controller for LifePO4 Batteries

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Originally Posted by noelex 77 View Post
For those that have not seen this sort of display before this is a result from my MPPT controller in typical conditions near the middle of the day

The 330w of panels I have are actually producing 310w.

The input voltage (or Vmp if the controller is doing its job) is 15.8v. The battery voltage is 14.0v. The voltage conversion is raising the input current from 19.6 A to 22.0A.

As I have mentioned the display is fibbing slightly on current, but my display is reasonably accurate around 20A so this is not far off reality.
What is the brand of controller Nolex? outback?
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Old 13-03-2014, 00:14   #160
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Re: MPPT Charge Controller for LifePO4 Batteries

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What is the brand of controller Nolex? outback?
Yes
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Old 13-03-2014, 00:24   #161
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Re: MPPT Charge Controller for LifePO4 Batteries

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Can you please tell us which cheap Chinese controller you used?

It's the Eco-worthy 20A MPPT solar controller. $102 with free shipping from China.

20A MPPT Solar Charge Controller Free shipping |Eco-worthy


I'm not endorsing it, or saying it's a great one, but I have been using it on a system with 2 x 205w Sharp panels charging 4 x 6v golf cart batteries. I can turn on the 110v fridge which then draws 29A from the system through a Xantrex inverter, if the batteries are floating, the controller immediately goes into bulk mode and will top out at about 22A @15v output. The panels are a bit large for the 20A controller, a better match would be around 300-330w for a 20A controller, but I got them cheap so I didn't really care.

One interesting side effect is that although I'm not getting the full 410w at peak sun, I am getting closer to 20A earlier and later in the day than I would have with 300w of panels, kind of a longer, flatter power curve. Considering my panels are mounted flat and don't track the sun, this is working out OK, producing an alleged 20-22A for a cheap setup costing only $400 plus cabling.
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Old 13-03-2014, 00:30   #162
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Re: MPPT Charge Controller for LifePO4 Batteries

Looks decent! So you can adjust max voltages, absorption times, disable temp comp etc? Might be suitable for a lithium bank.
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Old 13-03-2014, 00:44   #163
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Re: MPPT Charge Controller for LifePO4 Batteries

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Originally Posted by socaldmax View Post
into bulk mode and will top out at about 22A @15v output. The panels are a bit large for the 20A controller, a better match would be around 300-330w for a 20A controller, but I got them cheap so I didn't really care.
It is a shame to throw away power because of the limit of the controller, but if you have excess its not really important.

The controller has to protect itself to limit the current and it may be doing this by selecting a higher input voltage than the true Vmp perhaps giving you the impression the Vmp is higher than it is in reality.

15v is a bit high for the bulk voltage of most batteries.

The maximum of 20A is usually governed by the current rating of the components used. 22A suggests the meter is over reading (most likely) or the protection circuitry is slightly miscalibrated. Try and keep the ventilation up with the controller operating at its peak for long periods of time.
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Old 13-03-2014, 00:46   #164
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Re: MPPT Charge Controller for LifePO4 Batteries

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Originally Posted by noelex 77 View Post
For those that have not seen this sort of display before this is a result from my MPPT controller in typical conditions near the middle of the day

The 330w of panels I have are actually producing 310w.

The input voltage (or Vmp less wire losses if the controller is doing its job) is 15.8v. The output voltage is 14.0v (battery voltage plus wire losses). The voltage conversion is raising the input current from 19.6 A to 22.0A.

As I have mentioned the display is fibbing slightly on current, but my display becomes reasonably accurate around 20A so this is not far off reality.
Very nice!

It's indicating 15.8v from the panels, what is the advertised Vmp?

According to the display, 309.68 watts coming in, 308 watts going out. You're getting an indicated 22A from 330w of panels. That falls right in line with the owner's manual for the Eco-worthy controller, which recommends 300w of solar panels for a 20A output.
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Old 13-03-2014, 01:02   #165
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Re: MPPT Charge Controller for LifePO4 Batteries

Do you know if the controller manual is available online?
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