New Fridge Battery Drain

[sasto]

I have a 115 minute reserve capacity battery. I installed a DC fridge that draws 5 amps...while running. I understand this 115 minutes is @ 20 amps. So let's say at 5 amps, do I have a capacity of 450 minutes 'till fully discharged?

What is this draw going to do to my CCA's?

I really have more questions, but my brain can only handle a little at a time.

Thanks!

 

[Silvertip]

Re: New Fridge Battery Drain

You have the numbers partially correct. If the reserve capacity is specified at 20 amp draw and your fridge draws 5 amps while running, it does mean that "theoretically" the fridge should run for 460 minutes (115 x 4 = 460). However that means the battery would no longer provide the 5 amps required to run the fridge. It does not mean the battery is stone dead. Hopefully you are not using the same battery to start the engine as you seem to suggest. If so, that is a recipe for a "no start" situation. Another factor here is that the fridge does not run constantly so if one factors in a duty cycle where the fridge runs 25 minutes each hour then the battery should meet spec for nearly double that time. Again, you cannot reliably run the fridge off the starting battery (at least for very long) and be assured the engine will start. CCA and reserve minutes are not directly related. The CCA spec merely indicates the maximum cranking amps the battery is capable of delivering. The length of time it can deliver 350 starting amps is very short. Yes -- deeply discharging the battery will affect the CCA. Amps are amps. Use too many and there may not be enough left to start the engine.

 

[sasto]

Re: New Fridge Battery Drain

Thanks, Silvertip.

I do have a two battery system. On this boat I never dedicated a battery as house or starting. I may just do that.

If she were yours...under normal circumstances...how long would you run the fridge and still be able to fire up.

Numbers are what I'm looking for, but reality is the biggest factor. This will give me a clue.

 

[Bondo]

Re: New Fridge Battery Drain

Thanks, Silvertip.

I do have a two battery system. On this boat I never dedicated a battery as house or starting. I may just do that.

If she were yours...under normal circumstances...how long would you run the fridge and still be able to fire up.

Numbers are what I'm looking for, but reality is the biggest factor. This will give me a clue.

Ayuh,.... Can ya run it on shore power while on the hook,..??

I put 1 of those portable refs that look like an ice cooler in my pickup years ago,...
The 2nd time I went to leave a jobsite, 'n both my batteries were Dead, was the last time that thing rode in my pickup...

 

[bruceb58]

Re: New Fridge Battery Drain

I would never run the fridge on any battery I was expecting to start the engine with. Also, you never want to discharge any battery below 50% or you will be affecting its total capacity in the future.

 

[MH Hawker]

Re: New Fridge Battery Drain

Are you planning on a long hot summer and keeping a lot of beers on hand. snickers

 

[Silvertip]

Re: New Fridge Battery Drain

Thanks, Silvertip.

I do have a two battery system. On this boat I never dedicated a battery as house or starting. I may just do that.

If she were yours...under normal circumstances...how long would you run the fridge and still be able to fire up.

Numbers are what I'm looking for, but reality is the biggest factor. This will give me a clue.

You have two batteries but have not designated house/starting. Does that mean you simply have them connected in parallel? If so, you need a dual battery switch or ACR or you will undoubtedly end up at some point with a starting issue. Two batteries in parallel are the same as having one big battery. With a switch or ACR you can prevent the starting battery from being discharged along with the house battery. $30 for a switch or go for the ACR if you are switch challenged. Both have been discussed to death here so use the search feature for various installation methods. Or just follow the instructions that come with the device.

 

[sasto]

Re: New Fridge Battery Drain

Ayuh,.... Can ya run it on shore power while on the hook,..??

QUOTE]

Yes, Bond-o. I have shore power and have this battery on charge while at the dock.

I would never run the fridge on any battery I was expecting to start the engine with. Also, you never want to discharge any battery below 50% or you will be affecting its total capacity in the future.

That's my point, Bruce. I don't believe my Chrysler 318 inboard will start at near or below 50%. I am figuring maybe 80%. What are your thoughts on what % charge this engine will start at?

Are you planning on a long hot summer and keeping a lot of beers on hand. snickers

I have an AC fridge onboard (which dosen't run when out) for drinks....and a cooler. I keep food in this one. Yes, Hawker. I am planning on a long hot summer....I hope!

You have two batteries but have not designated house/starting. Does that mean you simply have them connected in parallel? If so, you need a dual battery switch or ACR or you will undoubtedly end up at some point with a starting issue. Two batteries in parallel are the same as having one big battery. With a switch or ACR you can prevent the starting battery from being discharged along with the house battery. $30 for a switch or go for the ACR if you are switch challenged. Both have been discussed to death here so use the search feature for various installation methods. Or just follow the instructions that come with the device.

Yes, Silvertip. I have a battery switch. Normally I switch batteries on each outing. I have been wiring up large boats for quite some time as a boatbuilder (in the past), but I'm no engineer. I currently have 2 battery chargers onboard. One is a trickle 2 amp and the other is a 6 amp. For the sake of this question, I will name batt 1 as a starting and batt 2 as house. At this point the 2 amp is hard wired to batt 1 and the 6 amp to batt 2. I am thinking of wiring the 6 amp to the battery common. What are your thoughts!

Are you sure about the five amps? Seems awful low and if it's correct thats not much cooling at all.

I was suprised as you Bubba. Yes 5 amps. Double checked. I actually have it turned to 4 out of 7. Suites my needs and cycles off quite frequently. I will gladly give you the info on fridge if needed.

 

[Don S]

Re: New Fridge Battery Drain

You need one of the Bluesea add a battery setup installed. Then you don't do anything but turn the battery switch to on, and go boating. When wired correctly, you can shut the engine off, run the fridge till you kill the battery and never touch the starting battery. Then when you start the engine, the house battery will get recharged. With you never touching the battery switch.

Add-A-Battery - 120A - Blue Sea Systems

http://www.iboats.com/Blue-Sea-Syst...0157784--session_id.559227902--view_id.729810

 

[sasto]

Re: New Fridge Battery Drain

I thought about that Don. I would really like to just switch batteries each outing. My main concern/question is how long would you run the fridge without a charge and still expect to start the engine? I would like to run the house and engine off of one battery, then if needed...use the other battery in an emergency. I would then switch back to the discharged battery and charge it with my alternator on my return trip.

 

[Don S]

Re: New Fridge Battery Drain

My main concern/question is how long would you run the fridge without a charge and still expect to start the engine?

That is an impossible question to answer.
Depends on exactly how many amps it takes and for how long to start your particular engine, and how long the fridge runs each cycle, and how many times the door gets opened and closed, and the condition of your battery.
Old batteries gradually get worse over time.
Now add in any other electrical usage on the boat during the time (stereo, lights, etc.) and there is just too many unknows.

 

[sasto]

Re: New Fridge Battery Drain

That is an impossible question to answer.
.

Kinda what I figured, Don. I spend alot of my time on this boat. I sleep on her at the dock frequently. She is somewhat my office. She would "turn over" slowly 'till I recently rebuilt the starter. The batteries are a couple years old. I seldom run any other DC, except maybe the stereo once in awhile.

Maybe the best thing for me to do is experiment at the dock. If she dosen't suit my needs....I guess I will just turn the fridge when not running the engine, if needed.

Thanks!

 

[sasto]

Re: New Fridge Battery Drain

That is an impossible question to answer.
.

Kinda what I figured, Don. I spend alot of my time on this boat. I sleep on her at the dock frequently. She is somewhat my office. She would "turn over" slowly 'till I recently rebuilt the starter. The batteries are a couple years old. I seldom run any other DC, except maybe the stereo once in awhile.

Maybe the best thing for me to do is experiment at the dock. If she dosen't suit my needs....I guess I will just turn the fridge off when not running the engine, if needed.

Thanks!

 

[Don S]

Re: New Fridge Battery Drain

If you spend that much time on the boat, then why not fix it up so you don't have to worry about a dead starting battery?

 

[bruceb58]

Re: New Fridge Battery Drain

Seems to me that the starting battery needs to be totally seperate from the fridge. My dad's boat that had a fridge on it had one battery dedicated to the fridge.

 

[sasto]

Re: New Fridge Battery Drain

If you spend that much time on the boat, then why not fix it up so you don't have to worry about a dead starting battery?

I'm not sure what you mean, Don. I will always have a battery to start with. Am I missing something?

Seems to me that the starting battery needs to be totally seperate from the fridge. My dad's boat that had a fridge on it had one battery dedicated to the fridge.

It really is, Bruce. On any given day I can choose between 2 batteries. One for house, and one for starting. I thought it might be a good idea to keep one battery fully charged if needed to start. If I do run one battery down, I can use the other to start......then switch to the dead battery and charge it using my alternator.

 

[bruceb58]

Re: New Fridge Battery Drain

Ok...so you are never in a situation where you can't start. You always have that one battery that is fully charged still.

 

[sasto]

Re: New Fridge Battery Drain

Ok...so you are never in a situation where you can't start. You always have that one battery that is fully charged still.

Yes, Bruce. I remember a reply by you one time where you gave numbers on a draw such as this one. All things being perfect, which they aren't. How long can this fridge run before I can't start the engine on the same battery?

 

[bruceb58]

Re: New Fridge Battery Drain

As usual it depends.

Depends on how old the battery is and how many times it has been discharged and how deeply. Every time you discharge and recharge a battery, you lose a little bit of its capacity. You lose more the deeper you discharge it. So if you like to discharge it more than 50%, you start losing a lot of its capacity. The 50% point is around 12.0V so I personally would not go further than that. If you need to discharge more than that, I would get a bigger battery.

Not sure how much room you have but I would dedicate 2 6V Trojan batteries in series to a fridge and add it to the 2 you already have. A fridge is a heavy hitter especially in Florida.

I am assuming your fridge is a compressor type. Make sure all your condenser coils are perfectly clean with no dust and lint on them. That will help your battery usage.

 

[sasto]

Re: New Fridge Battery Drain

Thanks for the informitive and quick response, Bruce.

50% is 12v. Good to know. I am more interested in my long term battery life than I am keeping my stores cold. I can always turn off the fridge while at anchor if needed.

I have room for the batteries. I am very familuar with the Trojans, just bought them for the golf cart. If my boating habits change where I spend more time at anchor, I will take your advice.

Yes, compressor. I will also take your advice on keeping the coils clean.

Thanks!