How much inverter power is needed to start a mini fridge?

[lrrowe]

Dustboy, I am nervous for you. Are you concerned for the moisture you might get inside your electrical work while driving in the rain and then have it present when you start to go live with power to the components? I am not saying I am right with this concern, just cautious.

[dustboy]

Don, good suggestion.

I suspect mobile audio geeks must have less money than yacht owners. I ordered this inline fuse block, plus two spare fuses and it was still half the price of the Blue Sea unit, and it seems better protected:

http://smile.amazon.com/gp/product/B00SG9HJE2/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Bob, thanks for the concern, somehow this makes me feel better:



Because the vehicle chassis and inverter are grounded together, any stray AC voltage traveling through moisture would shunt to ground. The manual on the Xantrex website shows this inverter with a GFCI outlet, which oddly this one does not have.

[lrrowe]

[dustboy]

Okay, here's a bit of data for you:

Battery: Single 12V Group 24DC
Solar: UPDATE: I have been victim of false advertising by Coleman/SunForce. The kit I bought clearly advertised an 85w panel, but I have since looked for the same kit and it says 15 watt. Reviews on Amazon confirm same. Spent $120 on that kit and for that price I almost could have had the Renogy 100w kit. Sigh.
Inverter: Xantrex X1000
Refrigerator: Kenmore 4.4 cu ft mini fridge

Started the fridge halfway cooled (it was cold and sat without power for 1 hour) at about 11 am. It was a warm sunny day, about 80 degrees. Battery read 12.73V. According to the chart here, that is 100% http://www.solar-electric.com/deep-cycle-battery-faq.html#Battery%20Voltages (voltage readings are a little skewed due to solar input).

At 11 am the next day, the battery was down to 12.06V, which is 50%.

So, 24 hours ain't bad. If I could get 2 days, that would be fine, as we rarely stay in one spot for more than a weekend, and the TV can charge the battery after that.

Granted, this is with no load from other appliances, such as lights or water pump. My conclusion is that the battery capacity is sufficient. With more solar capacity, I think we could gain a couple of days before the battery needs a charge from the TV. What do you think, would another 100w panel do it?

[GuitarPhotog]

The problem with your calculations is that you never want to run your battery down to below 50% charge, so you're at 24 hours, not 48.

<Chas>

[dustboy]

Which, er, I meant to say was that if I added another solar panel (this time a REAL one, dagnabbit) and got 2 days that would be the bee's knees.

Have a line on craigslist for some 80 watt BP brand polycrystalline panels, dude is asking $1/watt. Think I'll get 2, reckon that should keep us with chilled prune juice indefinitely. 'Course then I'll want the MPPT charge controller to go with it...yes this is what we call the "snowball effect"!

[MtnDon]

PWM vs MPPT charge controller. Going off on a tangent; hope nobody minds....

With a small PV system it can be a crap shoot as to what controller is best.

80 watt panels will have a Vmp voltage of around 17 to 18 volts and a maximum amp output close to 5 amps. The 17 - 18 Vmp is about ideal for charging a 12 volt battery. We need some voltage cushion to cover hot days, as voltage drops as panels get hot. We need around 14.4 volts to get a charge going into a 12 volt battery. We also need a voltage cushion for less than ideal sun to PV angle.

MPPT controllers really shine when we have large distances between the PV panels and the CC and the batteries. That will let us place the PV in series, double the voltage (with 2 panels) and keep the current the same. Low current = smaller wires needed to achieve best performance. Panels in series like that will require an MPPT charge controller. PWM controllers would waste a lot of power with panels in series. Put simply the MPPT controller takes the high volts and makes the CC output just high enough to charge the battery at its present state of discharge. The extra volts get changed into higher amps output.

Panels in series have some drawbacks too. Any shading on one of the panels will cut the output of not only the shaded panel but any other panels connected to it in series. One other disadvantage is the price difference, easily 3x that of a PWM, sometimes more. Conversely if we have two panels in parallel one can be 100% shaded and the other in bright sunshine will produce full power (in ideal conditions). A PWM controller can work fine in that case.

If you have good, non shaded sun, on both series connected panels you will also start producing power earlier in the day and continue later in the day. That's good.


If you are spending $1 a watt for 80 watt panels that is a good price on that size panel. But look around locally. You may be able to find a local company whose main business is installing residential solar power. The panels they use these days are frequently less than $1 a watt. They are larger, 250 watts and up, but will roof mount fine. Their voltage will require an MPPT charge controller. So IF you are bent on having an MPPT you may be able to have newer, more powerful panel for the same $/watt, or less, as those 80 watt panels.


Just trying to say that an MPPT CC is not always the best deal, but sometimes is needed. Small PV systems can be more difficult to design than larger ones.

[dustboy]

Huh! Good stuff to know, although this business of designing a solar system is turning out to be way more complex than I thought. These 80w panels have a Vmp of 32V so I think they will not work without a MPPT. Here are the specs:

http://www.posharp.com/bp-apollo-980-solar-panel-from-bp-solar_p1695817616d.aspx

I'm not married to these panels, there are some other deals on craigslist that might be a better bet. Also some 12 year old Kyoceras on eBay for under a buck/watt. By the time they're clapped out we'll have solar powered hoverboards.

[MtnDon]

Those are strange 80 watt panels. They would need an MPPT for charging 12 volt systems.

[twinight]

I use this type of fuse and bolt it directly to the battery and cable without a fuse block.
http://www.amazon.com/Fuse-Mega-32V-125A-card/dp/B001FXGLE0

[dustboy]

Picked up this big dog on craigslist, a 190 watt panel that takes up near half the roof. The little black panel aft of it is the not-85-watt-but-actually-15-watt panel that I had before, now to figure out what to do with that.



The new panel runs about 36 volts, so a new Tracer MPPT is on the way. All in, this little project will be about $300, and I will have lots of power to play with.

[jss06]

That looks like the same panel I run. 190 watts is nice to have when you also have a 12 fridge.

[dustboy]

JSS06, it's a Solaria 40" x 65". I tested the panel out in the guy's yard, on a cloudy day it was only pushing about 40 watts. Which is a little concerning because we sometimes are parked in shade. He said these panels are a little underrated, at full sun he said it would make over 200w.

[Gold5one]

A few years ago I tried building a small solar panel- it worked, but not for long, as moisture soon corroded the panel and expansion cracked a solar cell. Here is a picture of a solar cell- it is fragile silicon measuring only .016 inch in width. If you just breath heavy they will break. I have a 120 watt commercial panel that I was going to use on my build, but I decided it wouldn't take the vibration. IMO, the bigger home use panels will eventually fail on a camper- don't go over 40 watts in size per panel. The ones that RV stores sell are built better, so they can handle the vibration. Unfortunately, they cost considerably more money. I have a 5 watt epoxy panel I am going to roof mount for a battery top up charger- neither rain nor hail nor wind will destroy it. I saved that big solar cell panel money and bought a 800 watt 120VAC generator for $89- it has a 100 watt (8.3 amps) DC battery charging outlet, too.
There are some panels that use a style of silicon that is flexible and while they have lower output, I think they might survive better.

[dustboy]

Got the 20A Tracer MPPT charge controller. This thing is cool!

It needs a better home away from the water system. I'd like to use an enclosure but I'm afraid it will get too hot. Don't really have a good place inside the trailer.

Ideas?