Solar panel to recharge battery from fridge drain?

[Superu]

Since my trip is approaching fast and I haven't had time to install a dual battery setup, I'm thinking of alternatives to keep the battery going on the off days when the vehicle is stationary without having to leave it idling.

Here's my thought and what's been done so far.

• Install permanently hot 12v outlet in cargo area. DONE (West Marine twistlock)
• Purchase Sunsei Solar Charger SE-1200 & Sunsei Charge Controller CC-10000. Shipped cost for both less than $200.
• Run my Engel MT45 from the hot outlet.
• Use SE-1200 (Power: 1200mA, 15V (18W) ) to top off battery during the day when the car is sitting and we are hiking, swimming, etc.

The car will be run for several hours on various excursions at least every other day and I'll have a fully charged boost pack with me just in case. I estimate the longest the fridge would be on battery and solar charger is upon first arrival and setup. Potentially 36 hours with 16 or so at night.

The Engel will be set at 1 to maintain standard fridge temps. No freezing necessary for what we're bringing. Every test I've found indicates that draw from the fridge should be between .8 and 1.5 amps depending on outside ambient temperatures when set to run as a fridge.

The battery is an D34 Optima Yellow Top that is rated as follows:
Capacity (C/20 Rate) 55ah

The solar powered roof vent will help prevent excessive heat buildup inside the car.

Thoughts on the efficacy of this system would be greatly appreciated.

Thanks,
Bill

[Ursidae69]

I googled the SE-1200 and it looks like it is 18 watts. Is that right? According to my math that would be about 1.5 amps in good light, and if that is right, that would be less than average fridge usage during the day. I'm just learning myself though, so please post up your real world results. Good luck.

[Superu]

Forgot to mention that the MT45 is wrapped in the Engel Transit bag which provides for better insulation than normally would be achieved. Also, although the car may be in the sun, the fridge itself will be sheltered from direct sunlight. Thoughts? Anyone?

[Nuclear Redneck]

Talk to Mario at Adventure Trailers. He has a good knowledge of solar power and the Engel fridges. I'm sure that he would be able to steer you in the right direction.

[tdesanto]

I think at 18W maximum, the panel will extend the useable power of the battery, but not indefinitely. You can only get power during the day (sorry to overstate the obvious), but the fridge will run full time. Also, the solar panel won't always be at the optimum angle to maximize power collection.

So, at maximum collection, the solar panel is effectively putting back into the battery what the fridge is taking out. So, you're probably only draining the battery for about 12-14 hours/day.

I have that fridge w/transit bag and I have a group 31 Optima. I've run my fridge for over two days without any solar charging and still was able to start the vehicle (keep in mind that this is a bigger battery than the group 34). So, since you say that you'll be running the alternator somewhat at least every other day. I think you're probably good to go. I would definitely keep that backup battery booster handy, just in case.

[Superu]

After input from tdesanto and a conversation with ICP Tech Support, I ordered up the following from West Marine.



CHARGER, SOLAR 1500MA, SUNSEI

• Battery type:12V vehicle
• Current, output:1500A
• Voltage, output:15V
• Length / Height, external:30mm
• Width, external:350mm
• Depth, external:1048mm
• Power rating:22.5W
• Weight:4.3kg

10A CHARGE CONTROLLER

• Ideal for use with solar panels/ chargers generating up to 10A of current
• Reduces system maintenance, prevents overcharging of 12V batteries
• Protects all 12V battery systems and ensures batteries reach maximum capacity
• LED charging status indicator
• Avoids solar panel overcharging of battery systems
• Integrated screw terminal connections for easy installation
• Built-in surge protection and automatic reset for battery protection and ease of operation
• Reverse polarity and reverse current protection
• 2 year manufacturer's warranty

Should arrive by Tuesday next. Will report back on test results before the trip and will follow up with info in the trip report for anyone interested.

[elcoyote]

Measuring consumption on an Engel 45 at our shop using a "Doc Watson" from www.powerwerx.com, we have seen daily consumption of 20 to 28 A/h per day at 12 VDC on the "Ref" setting (around 38-40F) with ambient temps is the 70-80F range. Our experience with solar panels is that unless they are mounted on a tracking system, perfectly aligned for latitude and the season, the weather is cool and the the sky is un-obstructed by clouds, we can only expect 70% performance. This means for example that a 100 watt panel will only produce 70 watts per hour. This means 5.8 A/h rather that the rated 8.33 A/h @ 12 VDC.

So...if you were to back into the consumption of an Engel 45 you would need 60 to 80 watts of PV based upon 20 to 28 A/h of consumption per 24 hr period for a PV to keep up with your needs on the "Ref" setting on the MT-45.

The 22.5 W panel per our calculations will produce as follows: 22.5W/12VDC = 1.875 A/h x .7 = 1.312 A/h x 6 hrs of average usable sunlight = 7.85 A/day ( 6 hours is based upon information from sources such as http://www.energyatlas.org/contents/default.asp). Considering that your draw is 20 to 28 A/h per day, you will be coming up short 12 to 20 A/h short with 22.5 watts.

I know this is a lengthy explanation but is is based upon Ohms law:
Watts / Volts = Amps. As in all equations, you can flip this around such as Amps x Volts = Watts etc. Throw in the factoring of .7 to the PV for performance and you will not be disappointed.

Based upon these formulas and numbers, we supply 80 watt panels to our trailer customers who express a desire to be "self contained" with their fridges and laptops for indefinite periods. The calculations have been successful to date.

I hope this will help you in your solar endeavors.

[Superu]

Mario,

Thanks for the excellent feedback.

On this particular journey, my aim is not to fully keep up with the draw from the Engel, but to offset it enough that I won't drain my Optima beyond its reasonable capability to start the engine when required. Cost is a consideration, as well as storage space for the panel which is why I'm trying this route initially before possibly having to increase the PV power.

Without precise test equipment at my disposal, I've started my basic examination by loading my pre-cooled Engel into the transit lock in the back of the Superu last night and allowing it to run as a reefer for a 12 hour period until starting this morning for work. Voltage was still comfortably above 12 volts prior to starting and I then ran at highway speeds for 70 minutes to reach my office.

The car is now sitting outside my office window keeping my lunch cold and I'll see where the battery sits on the voltmeter mid-day and then again when I leave much later today. I am able to monitor the interior temp of the Engel so I'll track that as well.

My plan forward until the panel and controller arrive is to run the Engel from 7:00 pm this evening until 8:00 am Sunday which will effectively simulate the longest length of time it will be run on our camping trip without the engine being run to recharge the battery.

Should be interesting to see where we are on Sunday morning and also what impact the charger has come Tuesday.

[elcoyote]

Mario,

Thanks for the excellent feedback.

On this particular journey, my aim is not to fully keep up with the draw from the Engel, but to offset it enough that I won't drain my Optima beyond its reasonable capability to start the engine when required. Cost is a consideration, as well as storage space for the panel which is why I'm trying this route initially before possibly having to increase the PV power.

Without precise test equipment at my disposal, I've started my basic examination by loading my pre-cooled Engel into the transit lock in the back of the Superu last night and allowing it to run as a reefer for a 12 hour period until starting this morning for work. Voltage was still comfortably above 12 volts prior to starting and I then ran at highway speeds for 70 minutes to reach my office.

The car is now sitting outside my office window keeping my lunch cold and I'll see where the battery sits on the voltmeter mid-day and then again when I leave much later today. I am able to monitor the interior temp of the Engel so I'll track that as well.

My plan forward until the panel and controller arrive is to run the Engel from 7:00 pm this evening until 8:00 am Sunday which will effectively simulate the longest length of time it will be run on our camping trip without the engine being run to recharge the battery.

Should be interesting to see where we are on Sunday morning and also what impact the charger has come Tuesday.

You're welcome. Your testing approach sounds like it will give you a good feel for your battery capacity. I would suggest that you monitor temperature inside your vehicle if you can as your fridge compressor will be drawing more as the ambient temperature rises. This way you can put a correlation together of draw vs. ambient temps.

[JIMBO]

This is probabky a little late, but we go back from the Sierras yesterday afternoon and I put a short blurb, in the completed adventures

Here is the solar system I use, for my KOOLATRON and it has worked all summer, but I just got the ENGEL MT40 from Martyn, so we'll see a definate increase in my cooling abilities

-JIMBO