Solar or Wind???

[walt]

I hope this is not taken personal at all - this is just how I might deal with the fridge - it certainly would be nice for this trip I would take with my wife and dogs. Its a couple years off so I’m still undecided.. leaning towards the simple side of things (ice chest only). But anyhow I had made this spread sheet that made looking at some options somewhat easy so Ill post them.

This is based on the battery test numbers that Maine Sail provided in this thread and scaled for two golf cart batteries with a capacity of 225 amp hours.

50% capacity = 112.5 amp hours
80% capacity = 180 amp hours
40 amps charging current = 0.18C
Delta between 50 to 80% = 67.5 amp hours

The charging numbers (Maine Sail) showed you could charge at .2C from 50 to 83% battery capacity. So this assumes that with the 225 amp hour battery, you could charge between 112.5 to 180 amp hours with a constant 40 amps - with batteries in good condition. To get 40 amps charging, I would use a 40 amp three stage battery charger (AC input) and a 1000 watt gas genset. Genset somewhere near the rear of the boat, battery charger near the batteries at the front of the boat. This would require 110 AC to be strung along the lenght of the boat - which is almost no issue for power loss in cables (higher voltage is better for long runs) but would have some safety considerations.

The solar estimate here should not be taken too seriously as this can vary a lot - but at least you can see what was used. MPPT vs PWM would change the solar output by about 10% but daily variations are likely a fair amount larger than that so I didnt bother with that detail. For the larger panel, use MPPT, I currently only need PWM for my smaller setup. Since solar can vary a lot, I think if you stay out very long, you pretty much need to bring along some method (such as a gas genset and charger) to compensate for a string of cloudy days. The more solar you add, the less chance of needing the gas genset - but you probably still need to bring it along if there is any chance of more than two or three cloudy days. Total daily amp hours used is based on my normal 15 amp hours plus 35 for the fridge = 50.. The fridge certainly complicates things, the charging is way simpler with just an ice chest.

Keep in mind this is a sailboat with an under 10 hp outboard and corresponding small charging system. Also another thing this points out - being able to tell the battery state is "kind of" important here. You probably could get by just watching voltage.. but either a charge monitor or something like the Balmar battery voltage monitor might also be good to have (and make the boat more complicated.. more expense.).

The first configuration is with my current 50 watt solar panel (40+10). I could go for about four days without using the genset and then would need to run it about an hour every other day.

The config below is with a 100 watt solar panel. It pretty much would supply all the power I needed (still plenty of power after nine days)

Finally the last one (below) is with 50 watts of solar and no extra charging. I could go for about 4 days starting with a full charge and getting good solar everyday.

 

[MrBill_FLL]

Used with the batteries at or above 50% the most I ever saw it putting out was about 24 amps, way below the 60 amp rating.

That was only for the first few minutes of charge and they it would continue downwards from that point and within 30 minutes or less it would only be putting about 10-12 amps into the batteries. At this point we are at diminishing returns so I would stop and let the solar top the batteries off while they also supplied the power for the fridge.

...
A lager alternator would do nothing to increase the charge time with our batteries. Now there are other charge circuits that can be made that can force a charger to charge at a higher rate than the batteries acceptance rate. I didn't feel the need to go that way as you need to be very careful doing this.

The lager alternators come into their own when cruisers with lager boats have larger battery banks that can accept more and when at times they draw them down below 50%.

Are you saying the batteries determine how many amps are generated due to how much they can accept?

Or this is just typical of all alternators.

21 amps, is NOT what I expected to hear... out of a 60amp alternator...

 

[walt]

You should find your answer in posts 89 and 93.. The alternator should have been able to put out at least 36 amps (20%C) in the bulk charging mode - alternator or AC battery charger. If every thing was working correctly (the alternator regulator must allow voltages up to 14.4), you should also be able to put in this current from between 50% (90 amp hours) to 80% (144 amp hours) for a total bulk range of 54 amp hours.

2 group 27 Deep Cycle batteries are likely 90Ah each or 180Ah's for the two:

180Ah Battery = 36A of current to hit 20% of "C"

FYI, in all the cases I had posted in my last post, the one I like the best is just a 100 watt solar panel (or so..) and NO genset. If you ever get low on charge, just turn off the fridge and throw in a bag of ice, leave the fridge off for a couple days while the ice is good.. I have never seen these portable fridges but seems like a good assumption that a fridge has to be able to tolerate some water in the bottom.

 

[MrBill_FLL]

if only I could get FedEx to deliver ice in the 10k islands...

I don't have a fridge or solar, but do like to cruise where you can't get a bag of ice within 30 miles..


re-reading the posts, it sounds like the wire used between the alternator and batteries could be a bottle neck. or reason for the lower amps output.




snip:

You’re diagram shows #8 wire. I thought you had 4 gauge between the battery and the charger but if you are using 8 gauge, might be another reason you had relatively low current. You’re batteries are up near the front of the boat and the gas charger is near the rear so when its putting current out to the batteries (on the other end of the boat), it is sensing the voltage for when to cut back – at the generator. If you have a round trip of say 50 foot of 8 gauge wire, that has a resistance of maybe .03 ohms. This doesn’t seem like much but would drop 0.6 volts at 20 amps. So the sensing on the generator would think the battery voltage is 0.6 volts higher than it actually is and would cut back the current too soon.

and MS post
-snip-

Sumner it was a 20% of "C" / Ah Capacity charge rate. Battery was a 125Ah group 31. Just like your Group 27's it is an "adapted" for marine use battery.

20% of "C" occurs very similarly across all flooded batts.

100Ah battery = 20A Charge Rate
125Ah battery = 25A Charge Rate
90Ah battery = 18A Charge Rate

2 group 27 Deep Cycle batteries are likely 90Ah each or 180Ah's for the two:

180Ah Battery = 36A of current to hit 20% of "C"

12.5A would be a 7% of "C" charge rate.

The simple rule for current limiting / attaining absorption voltage is this:

The HIGHER the charge current rate the sooner you hit voltage limiting / absorption

The LOWER the charge current rate the later you hit voltage limiting / absorption

 

[alfred gamil]

one 12 volts dep cycle
my solar panl works very very well ,40n watts is much more than enough ,depnding on your consumtion of course ,i use it for lights ,gps , filling cll phone,filling inflatable dinghy,