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How much solar do I need to keep truck batteries charged?


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#1 tyates007

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Posted 03 November 2013 - 05:44 PM

I have never used solar power before but have read as much as I can find, which is a lot of conflicting internet info. Time has come to park the truck for the long Idaho winter. I will be getting it out occasionally to work on small projects. I would like to leave the batteries in the truck on a trickle charger or smart charger. Where I have the truck parked is enclosed with concrete floor and overhead door but there is not power. I have seen small solar kits for sale but have no idea what I would need to maintain the bank of 4 batteries. My wife bought me a 45 watt kit from the local HF store but I have never used it. Would 45 watt keep the batteries maintained? Any help or suggestions would be appreciated.

Edited by tyates007, 03 November 2013 - 06:24 PM.


#2 Randy retired

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Posted 03 November 2013 - 07:51 PM

I have a 33 watt panel on my truck and it keeps the batteries charged. In fact the batteries are usually fully charged by noon so you might get by with less. My truck is a 2001 and the newer models may use a little more power at rest but I would think 45 watts would be plenty providing the panels are not shaded. Snow needs to be removed.

Edited by Randy retired, 03 November 2013 - 07:54 PM.

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#3 SuiteSuccess

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Posted 03 November 2013 - 07:55 PM

Tyates007,

I have a 15 watt BatteryMinder solar but it is not enough to keep up with 4 big truck batteries when you factor in natural discharge plus parasitic draw and darkness. My 15 watt produces about 1.25 A Not being electrically inclined I would believe your 45 watt solar would be up to the challenge and should produce about 3.5 A. Maybe Jack and RandyA will chime in since they are the gurus.

Edited by SuiteSuccess, 03 November 2013 - 08:25 PM.

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#4 Jaydrvr

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Posted 03 November 2013 - 08:12 PM

As your 45 watt system will be producing about four amps, that should be plenty.  I have, on occasion, charged my three pack with a six amp charger.  While it did take 1.5 to 2 days, the batteries were weak and extremely low.  My truck is a '99; newer trucks may have more parasitic draw.  I would be more concerned with excess voltage, which can cook your batteries and ruin them.  


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#5 tyates007

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Posted 03 November 2013 - 09:16 PM

Would it work to just use a small inverter and plug a battery tender type charger in? That way I would not need to worry about overcharging. The charge controller on the kit has a 12v cigaret type plug for this purpose.

#6 Shallow Draft

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Posted 03 November 2013 - 09:42 PM

I use a 4 amp battery maintainer and it keeps up easily. So size a solar package to get at least 4 amps.
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#7 rickeieio

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Posted 04 November 2013 - 04:56 AM

And what would the power source be for the inverter? :o

Would it work to just use a small inverter and plug a battery tender type charger in? That way I would not need to worry about overcharging. The charge controller on the kit has a 12v cigaret type plug for this purpose.


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#8 tyates007

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Posted 04 November 2013 - 05:20 AM

In thinking about it I guess to use an inverter it would have to have an additional battery wouldn't it. There is a charge controller with the kit that has a 12v socket but that is probably to charge cell phones and such not run an inverter.

#9 Jack Mayer

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Posted 04 November 2013 - 08:31 AM

4 amps is plenty to maintain a fully charged 4-battery truck bank - even on the newer trucks. Assuming nothing wrong with the batteries. I like the Batteryminder systems because they desulfate well. There is a Batteryminder that will allow you to hook in your own solar panel. 


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#10 tyates007

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Posted 04 November 2013 - 09:17 AM

Thx Jack, I will check out the Battery Minder. Is the model scc180 that you are referring to?

Edited by tyates007, 04 November 2013 - 09:24 AM.


#11 tyates007

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Posted 04 November 2013 - 10:55 AM

Should I disconnect the bank from the truck so there is 0 draw or should I leave connected for ECM power purposes?

#12 SuiteSuccess

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Posted 04 November 2013 - 11:08 AM

4 amps is plenty to maintain a fully charged 4-battery truck bank - even on the newer trucks. Assuming nothing wrong with the batteries. I like the Batteryminder systems because they desulfate well. There is a Batteryminder that will allow you to hook in your own solar panel. 


Jack,

It is obvious after use over last winter my 15 watt (1.25A) BatteryMinder is inadequate to keep my truck batteries charged. If I bought the scc180 model could I use my 15 watt panel that I already have and add in a 25 watt panel for a total of 40 watts to get enough amps to charge and maintain my batteries? Or do the panels have to be "balanced" i.e. Two panels of the same wattage? Or would it just be cheaper to buy a bigger single panel, say 50 watts?
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#13 hone eagle

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Posted 04 November 2013 - 12:15 PM

Should I disconnect the bank from the truck so there is 0 draw or should I leave connected for ECM power purposes?

That is what I do ,yours may have a battery disconnect , mine is center of bank, high on frame a long arms reach in .

Took a year before I ran across it.

I turn if off every time I leave the truck sit a few days ,no ill effects. 

Starts right up and transmission 'skip shifts' first time - no relearning.


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#14 SuiteSuccess

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Posted 04 November 2013 - 12:20 PM

That is what I do ,yours may have a battery disconnect , mine is center of bank, high on frame a long arms reach in .
Took a year before I ran across it.
I turn if off every time I leave the truck sit a few days ,no ill effects. 
Starts right up and transmission 'skip shifts' first time - no relearning.


Is your disconnect on the positive side or negative since most of our accessories are frame grounded?
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#15 TS

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Posted 04 November 2013 - 01:48 PM

I always disconnect the neg first. Eliminates wires from flopping around and hitting or shorting to ground.

 

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#16 hone eagle

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Posted 04 November 2013 - 04:28 PM

Is your disconnect on the positive side or negative since most of our accessories are frame grounded

It is exactly dead center of the 4 batteries.I have to reach in blind and grope for it.Thats why I never knew it was there,Gregg never mentioned it and I always wondered if he knew about it.


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#17 Jack Mayer

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Posted 04 November 2013 - 05:00 PM

I would not buy the panel that the batterminder setup comes with. I would buy the solar charger they sell alone and add a panel myself. Probably whatever I could find at a low cost per watt up to 180 watts. That is the SCC-180. You do have to use a nominal 12-volt panel, NOT a high voltage panel in the high 20-volt plus range. Look for a panel in the Vmp=21V or less range.


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#18 RandyA

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Posted 05 November 2013 - 07:11 PM

I'm a little late chiming in.  But, here is my 2 cents worth of advice:
 
Lot's of variables - amount of sunlight, angle of panel to sun, build up of ice and snow or just plain old dirt on the panel.  Ambient temp around the battery(s) also influences charge/discharge.  Solar panel output may also influenced by temp but concern is more hot than cold.  Age and prior condition of the batteries is another factor.  The older a battery is the faster the self-discharge rate will be.

First thing is to disconnect your battery(s) from any external current drawing source.
 
Let's look at some "average" numbers.  Group 31 truck battery.  About 1 year old.  Outside temp average over 24 hours = 32 degrees F.  Battery disconnected from all external parasitic sources.  15 amp hours of self discharge per battery for a 4 week period under these conditions is a good number to work from.   For a bank of four batteries this will be 60 amp hours.  Convert that to watt hours - 12.6 x 60 = 756 watt hours.  Take the maximum sustained output of your HF solar kit.  45 watts out is really optimistic and only attainable under the most favorable conditions but we will use that figure anyway.  Divide 756 by 45 = 16.8 hours of sunlight needed capable of providing full output during a month.
 
You can run similar numbers for a 15 watt panel and the full output number goes up to 50.4 hours or 12 hours of sunlight capable of peaking the panel to full output per week.
 
Go back to initial variables of temp, battery condition, peak sun, etc. and the numbers can skew 200% or more - most commonly toward the lower values.
 
IMHO your Harbor Freight 45 watt package would make a good system - not Rolls Royce quality but good enough to get the job done unless you want to spend a lot more $$$.  As Jack noted the HF controller is a straight, single voltage output PWM module.  No de-sulfation mode but that is not as important on starting batteries as it is on deep cycle.  More important is maintaining a float voltage in the range of 12.3 to 12.6 applied to the batteries.  The HF controller does include a blocking diode to prevent discharge back through the panels when sunlight is too low to provide the unregulated input needed for the controller to function.

Edited by RandyA, 05 November 2013 - 07:14 PM.

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#19 Dave & Jenney

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Posted 05 November 2013 - 09:54 PM

Just a quick note, very good comments from Jack and Randy, they have a lot of common sense. A rule learned in my past life said:
     For wet cell lead acid batteries approx 1ma of maintenance charge per ampere hour of bank capacity.
  
Much more than that and you will be carrying a lot more water than you need to. Remember, this is just to keep them up,
If they are discharged, much more current will need to be available.
 
Because I have power I use a constant voltage charger set to 13.38vdc at battery terminals. Water needed twice per year.
Really like idea of solar for battery maintenance when not near power and am looking into small solar charge controllers, 

they are very inexpensive as are 100-200watt solar panels.

 

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#20 tyates007

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Posted 05 November 2013 - 10:22 PM

Thanks for all the replies. I will use the HF panels and see how it goes. I did order the scc-180 solar batteryminder to replace the one in the kit. Hoping to get it set up in the next couple of weeks. Ill report back on how well the setup does. I am going to be into the system about $215 including the batteryminder. This seems pretty reasonable in my mind compared to dragging all the batteries out of the truck.