Opinions on solar please ...

[basssears]

I agree the math doesn't add up, that's sort of my point. I'm just looking at specifications and they show me that the fridge is claimed to draw twice the wattage when running on 110/120 volts, so there's something about the way it's set up that makes it draw more when running on 110.

Another example item is Norcold icebox conversion (on Westmarine: NORCOLD SCQT-4408 Icebox Conversion Kit with Flat Evaporator | West Marine
"Power Requirements: 0.7A @ 120V AC, 0.35A @ 240V AC, 2.5A @ 12V DC, 1.3A @ 24V DC"
So we convert the AC numbers to watts and the DC numbers to watts using amps*volts=watts and we get:
AC: 0.7A*120V = 84 watts
DC: 2.5A*12V = 30 watts

So my conclusion (and I'm just going from specs here, maybe the specs are wrong on all of these, but my RV van fridge had similar specs) is that the fridge draws more than double the wattage when running off alternating current... why, I have no clue, but if the numbers from the manufacturer are right that's the only conclusion I can draw.

Originally Posted by newhaul

Sorry but your math doesn't add up if you have a draw of 30 watts it doesn't matter what voltage its still 30 watts which would mean 30 watts ÷ 12.5 volts nominal = 2.4 amps and 30 watts ÷ 110 volts= .27 amp draw thru inverter I would say you would draw about 3 amps at 12.5 non to provide .27 amps at 110 v ac.

[newhaul]

Originally Posted by basssears

I agree the math doesn't add up, that's sort of my point. I'm just looking at specifications and they show me that the fridge is claimed to draw twice the wattage when running on 110/120 volts, so there's something about the way it's set up that makes it draw more when running on 110.

Another example item is Norcold icebox conversion (on Westmarine: NORCOLD SCQT-4408 Icebox Conversion Kit with Flat Evaporator | West Marine
"Power Requirements: 0.7A @ 120V AC, 0.35A @ 240V AC, 2.5A @ 12V DC, 1.3A @ 24V DC"
So we convert the AC numbers to watts and the DC numbers to watts using amps*volts=watts and we get:
AC: 0.7A*120V = 84 watts
DC: 2.5A*12V = 30 watts

So my conclusion (and I'm just going from specs here, maybe the specs are wrong on all of these, but my RV van fridge had similar specs) is that the fridge draws more than double the wattage when running off alternating current... why, I have no clue, but if the numbers from the manufacturer are right that's the only conclusion I can draw.

OK now I see where the problem is the nor cold unit is rebranded Engel unit I have installed the and the power issue is that it uses an inefficient power converter to go from 110 volt dock power to the 12 volt power that the compressor runs on.

[basssears]

Gotcha, makes sense... I can't always seem to pull it off but when I can find out the "native" power of a device I always try to run it off that type of power, for exactly this reason... so if you know your compressor is 12v then if at all possible run it directly on 12 volts, no conversion, no loss.

Man that's serious loss on that convertor... 50%? Crazy inefficient...

Originally Posted by newhaul

OK now I see where the problem is the nor cold unit is rebranded Engel unit I have installed the and the power issue is that it uses an inefficient power converter to go from 110 volt dock power to the 12 volt power that the compressor runs on.

[darylat8750]

Originally Posted by basssears

Is fridge 12v or 110 only? I would not try running household current fridge off battery power through an inverter, very inefficient as you lose some in conversion but mainly because no fridge is as efficient (because they feel they don't have oto be I guess) when running at 110

As example, take Engel SCQT 4408F-U1-L ice box conversion...
12v is 1.3-2.5 amps or 16-30 watt draw
110v is 0.7 amps or 77watts... Same fridge, twice the watts... and you probably lose 10% through inverter so need of provide 85 watts to the inverter to have it output 77 watts.

If at all possible find 12v specific appliances when dealing with higher power draws.

Several of us use 120v refers to good effect. SailorChic has a lot of real world experience with something like you could use and she is a trained thinking person who knows the + and - of the thing.

[Ribbit]

Personally I'd avoid Lithium Polymer (LiPo) batteries on a boat (or in a house or car for that matter). They are VERY touchy, and if left for a while need to be discharged to a safe storage voltage. Great care has to be exercised in how they are charged, and how they are discharged. To the extent you can get explosion proof charging bags to put them in while charging (I have an explosion protection charging bag, and I use it), and shipping options can be severely curtailed due to the risks involved in carrying them. As Boeing and others have discovered, they are a bit prone to bursting into flames (as well as exploding).

Never let a 12v battery get below 12.2v, and it will last, and last (so called deep discharge batteries also get damaged if voltages go below this, and can only withstand maybe a bit more damage than 'ordinary' batteries, maybe not too). At 12.2v you are at about a 50% charge level.

An acquaintance has been testing solar panels for getting on 30 years. He hasn't had a monocrystalline Class A cell perform as low as specified age would indicate, ALL of them have surpassed their specification, and are still performing well at 20+ years.

He hasn't had a polycrystalline solar panel last usefully more than 5 years yet (hopefully that is changing/will change).

While MPPT charge controllers are very nice, it is possible to pick up extremely well made PWM charge controllers at very good prices (e.g. I got a pile of Highway Authority heavy duty 30 amp 12v ones for £10 each). I will use mine on the small 12v system which won't have many amps flowing through it (lots of amps at 12v are bad news for the infrastructure cabling, connections, and fittings). 15 amps through a 30 amp charge controller should help provide long term reliability, as well as sensible infrastructure costs (cabling for example gets seriously pricey, beyond 170 amps, and if you utilise a lot at 12v, amp handling ramps up really fast). For DC make sure your cabling is multi strand rather than solid core too. I know it works better, but it is supposed to be because DC travels on the outside of the strands, so the more strands the better (I am not actually that sure about that, but it is more flexible and easier to work with anyway, so any excuse I suppose, and I haven't felt the need to delve right into it as yet).

My 'serious' system (not on a boat) is 48v for the sensible amperages, and for that there will be a big MPPT charge controller, 48v battery banks, and I have a humungous 8kw/24kw 230v pure sine wave inverter (I can hardly lift the darned thing it is so heavy, almost all transformers).

You used to be able to get towed generators for boats, is there anybody still making them?

eta: Yes Aquair still do them.

[NorwestR]

Originally Posted by darylat8750

Several of us use 120v refers to good effect. SailorChic has a lot of real world experience with something like you could use and she is a trained thinking person who knows the + and - of the thing.

Thanks, will try to contact her ...

I had to step away for a few days, but was pleased to find the thread has continued the debate in addition to yielding me the kind of information I was hoping for. Now I've got a pretty decent rum line to follow.... Thanks everyone!

[RKsailsolo]

Originally Posted by zboss

Its called a battery monitor. A device called a "shunt" is part of how the monitor works. Lots o companies make them. For example:

BMV-700 series - Victron Energy

Here is one of the best:

Balmar SmartGauge Battery Monitoring System

Thanks for the link to the Balmar device. It looks like the most capable choice for long term monitoring.

[SSgtPitt]

[QUOTE=Davy J;1972189]I previously owned a Catalina 25 and outfitted it with a solar panel, charge controller, Engel refer and a small freezer. I constructed the solar panel mount from SS bimini rails and the clamps from a Magma grill.

Davy, i like your mount but am curious how it performed in high winds and heavy seas. I'll be doing the same thing soon and only want to do it once.

[exMaggieDrum]

Originally Posted by NorwestR

You are partially right, the device is called an ammeter, and true, it must be inserted inline(in series) to measure the current. Most modern day "multi-meters include all three functions of measurement. The device I had in mind, I believe, was somehow inserted between the device and the battery for a real time accurate reading on current draw. I was researching this a few years back, but can't find my notes ...

I stopped reading the thread after this post and the previous one from Art on multimeters. You do NOT want to insert a multimeter multimeter in line with the circuit unless it is a VERY small current. Your manual will tell you what the max amps can be. Otherwise you will blow a fuse inside (hopefully) or just burn out the meter. What you need for this is a clamp-on ammeter. A meter that is for ohms only (ohm-meter) will measure resistance but not amps, at least not directly, and not for what you want. You can put a "shunt" coupled with a digital ammeter (or combo volt-amp meter) to read the current. Clamp-on ammeters (multimeter) can measure both AC and DC current - buy one that does, anyway. Useful to have.

[perdunulpart]

Originally Posted by newhaul

I would guess the underestimation of fridge comment is directed at me. On our Spencer we have a 7 cf refer and 2.5 cf freezer it is a technautics cool blue spill down system and it draws approx 3.8 amps when running which figures to be about 4 hours per day. In summer and about half that in winter. Also a fridge is fine on a small boat dorm type run off of an inverter however that would require more solar than a single 100 watt panel.

simple way to know your draining power; watt= volt x amp for any item on your circuit

[newhaul]

Originally Posted by perdunulpart

simple way to know your draining power; watt= volt x amp for any item on your circuit

Yes that is the correct formula to figure the power usage. You just need to know two of the values to get the third value in the flrmula.
However it doesn't tell you that you are using power . A much easier way is to use a multi meter.

[mcarling]

Originally Posted by basssears

Gotcha, makes sense... I can't always seem to pull it off but when I can find out the "native" power of a device I always try to run it off that type of power, for exactly this reason... so if you know your compressor is 12v then if at all possible run it directly on 12 volts, no conversion, no loss.

Man that's serious loss on that convertor... 50%? Crazy inefficient...

No, there is no dramatic difference in efficiency. These fridges operate with two to three times lower power using DC which means their duty cycle is two to three times higher when operating with DC than with AC. For example, the refrigerator might operate 2 hours per day using AC but five hours per day using DC. The daily power consumption will be similar (though not exactly the same).