How much solar for small ice-box conversion?

[ozsailer]

Gday Argo Sailer,
without going into detail, all the previous answers are just plainly wrong !!!! Very first and I mean very first issue is what is the total load capacity of your boat including lights, instrumentation etc etc. If you have standard globes or halogen lamps these can be quite a burden on your system if you are sailing at night and can the storage capacity of your vessel. Also consider power consumption of radar, radio and navigation equipment including your auto pilot. Once you know the load over a 24 hour period then, and only then can you even consider working out what solar and battery capacity you require. When working out this calculation add in the fridge capacity power unit. Remember that with AGMS batteries you can only really use 40% of their total capacity. IE if they are rated at 100 Amphours you have only 40 amphours of useable capacity. Please talk to a professional about your needs, you will save yourself a lot of stress and incorrect information. I apologize if I missed a post with this detail previously.

Ozsailer

[sailorboy1]

Originally Posted by ozsailer

Gday Argo Sailer,
without going into detail, all the previous answers are just plainly wrong !!!!

good thing you came along then I guess

[newhaul]

Originally Posted by ozsailer

Gday Argo Sailer,
without going into detail, all the previous answers are just plainly wrong !!!! Very first and I mean very first issue is what is the total load capacity of your boat including lights, instrumentation etc etc. If you have standard globes or halogen lamps these can be quite a burden on your system if you are sailing at night and can the storage capacity of your vessel. Also consider power consumption of radar, radio and navigation equipment including your auto pilot. Once you know the load over a 24 hour period then, and only then can you even consider working out what solar and battery capacity you require. When working out this calculation add in the fridge capacity power unit. Remember that with AGMS batteries you can only really use 40% of their total capacity. IE if they are rated at 100 Amphours you have only 40 amphours of useable capacity. Please talk to a professional about your needs, you will save yourself a lot of stress and incorrect information. I apologize if I missed a post with this detail previously.

Ozsailer

Well so much of what you posted is wrong but I won't go into it as it would cause a major thread drift .

I do however suggest you actually read the entire thread before making any statements . it was all covered in the thread already.

[ozsailer]

Originally Posted by newhaul

Well so much of what you posted is wrong but I won't go into it as it would cause a major thread drift .

I do however suggest you actually read the entire thread before making any statements . it was all covered in the thread already.

Really - please expand for my own knowledge. Happy for you to PM me and point out where I am wrong.


Ozsailer

[newhaul]

Originally Posted by ozsailer

Really - please expand for my own knowledge. Happy for you to PM me and point out where I am wrong.


Ozsailer

Read the data here
https://www.emarineinc.com/Firefly-Group-31-FAQ

What is the Firefly’s G-31 lowest voltage the battery can withstand?

10.5V is fully discharged, 11.7V is @ 60-70% discharged. You can discharge them down to 80%, @ 11.5V as long as they are brought back up with a charge rate of at least .4C. (.4C is defined as 40% of rated capacity – one G-31 Firefly battery rated at 116 A-Hrs capacity, so periodically it is good to recharge with at least 40-46 amps. Multiply this rate if more than one battery in the bank by the number of batteries).

That is a good start for all considering the AGM option

This chart will provide to be extremely useful for any and all considering battery replacement.
Thanks Adelie for compiling it

[ozsailer]

Newhaul, I am not trying to be augmentative here BUT you have picked one battery from hundreds of AGMS that are made and marketed. Granted by the stats you provided that particular battery can be run down to a rated 65%. Please note the other AGMs state they can be run down to 50%. While the manufacturer states this can occur talk to any battery expert or electrical engineer and they will tell you that for maximum life you should not run a battery down to less then 40% of its capacity. IE 100 amp hour battery you can safely use 40 amp hours of its capacity. On hour previous boat we had 800 AH of battery capacity but I liked to keep the battery capacity no lower than 70% normally it was around 80-85% of capacity used on continuing sunny days. I think you will also find that for the voltages you mentioned that you can get down to the vast majority of appliance wills stop working due to low Votlage cutouts. If these are not installed you risk damaging the appliance. Just to clarify I am only talking AGM or gel batteries. Lithium are a whole different ball game. From my experience the very great majority of people do not understand or ask the right questions regarding electrical battery questions.

Ozsailer

[newhaul]

Originally Posted by ozsailer

Newhaul, I am not trying to be augmentative here BUT you have picked one battery from hundreds of AGMS that are made and marketed. Granted by the stats you provided that particular battery can be run down to a rated 65%. Please note the other AGMs state they can be run down to 50%. While the manufacturer states this can occur talk to any battery expert or electrical engineer and they will tell you that for maximum life you should not run a battery down to less then 40% of its capacity. IE 100 amp hour battery you can safely use 40 amp hours of its capacity. On hour previous boat we had 800 AH of battery capacity but I liked to keep the battery capacity no lower than 70% normally it was around 80-85% of capacity used on continuing sunny days. I think you will also find that for the voltages you mentioned that you can get down to the vast majority of appliance wills stop working due to low Votlage cutouts. If these are not installed you risk damaging the appliance. Just to clarify I am only talking AGM or gel batteries. Lithium are a whole different ball game. From my experience the very great majority of people do not understand or ask the right questions regarding electrical battery questions.

Ozsailer

Read the attached charts it covers a lot of different batteries and the numbers are real world for the most part provided by fellow,cruisers .
BTW Firefly’s are the predominate AGM in use on our boats.

[ozsailer]

Newhaul, no worries, you follow the guidelines - good luck. I will forget about my 40 years of of real life experience in the electrical game and sailing.I only ever try to offer real world advise based on my experience. I am still waiting what else I was wrong in given your post.


Ozsailer

[newhaul]

Originally Posted by ozsailer

Newhaul, no worries, you follow the guidelines - good luck. I will forget about my 40 years of of real life experience in the electrical game and sailing.I only ever try to offer real world advise based on my experience. I am still waiting what else I was wrong in given your post.


Ozsailer

Same here as a retired shipwright . BTW my bank is the LFP battery at the bottom of the chart.

[RedneckRedcoat]

Originally Posted by argosail

So I have a boat under contract, turns out she does not have a fridge. I was looking at either a ice-box conversion (12V) or portable fridge/cooler (12V). There is only 12V on the vessel.

I've seen various units with draws from 1A to 4A, so lets say an amp draw of 2.5A.

The boat is 35' LOA. Being on the hook in Florida/Caribs, I am wondering if 800W (2x400w panels) and 1 AGM house battery (standard size, that's all I know) will be sufficient. I would rather not change the battery set-up (because $$$).

I will likely go Adler/Barbour for ice-box conversion, or Dometic/Iceco for a fridge cooler.

I don't plan to have any cold alcohol on board, I don't plan to have oodles of frozen/cold food. A minimal set-up to keep fruits and veg, and sandwiches fresh. The icebox itself isn't huge, it's small for a 35'.

There would be no other systems running other than keeping starting battery (another AGM) topped up and radio, this is on the hook, not underway.

I know there is some formula but everyone seems to have their own version of how things work for them based on their unique set-ups??

I would do two batteries, you won’t get the full 800watts on cloudy days and cloudy days can span multiple days. Other than that your setup would work fine