DC refer questions

[noworries]

my house bank is 2 6V Costco golf cart batteries
my fridge is a Adler Barbour CU-100 w/ BD35 compressor and small vertical evaporator, installed in 2003
We're going on a 9 day cruise

Couple of questions...
how long can we expect to be able to run the refer?  We've done a 3-4 day cruise with no issues... I typically run the motor for about an hour every day to heat up the water and shower.  I'm guessing I never put back everything I take out... but it lasts.

As far as regular DC load, we have the stereo (JVC car stereo), freshwater pump, cabin lights are all LED, anchor light is not on the DC system.

Our refer has a drain in the bottom... is it worth covering that to keep cold air in?  I usually put a big block of ice in the bottom to help lower the load on the DC system... any other tricks?  Put a blanket over the top? 

Also did anybody ever come up with a better ice trays than those vertical aluminum things that don't like to hand over the ice once they're frozen?

[Ron Hill]

No:  Kind of hard to answer your question not knowing your electrical system and your amp usage per day !!
If you have the original stock alternator I'd say the answer is - no you won't make 9 days with out severely draining your 210 AH house bank.  You might want to find a marina half way thru the trip and plug in.

If you are using ice I wouldn't plug the fridge drain.  What I did was to put a piece of 1/2" pipe on the drain hose to the foot pump.  I also have a thermal pad that covers the entire top.

I found that if you leave the ice cube trays in the sink for about 30 minutes and the cubes will all come out easily.  Then take the extra cubes put them in a Zip lock and back into the freezer.

[noworries]

Marina's not an option.  I'm just going to plan to have some dry food for the last part of the trip.  You can drain the 6V golf cart batteries pretty low can't you?  Isn't that why they're better than 12V?  Just trying to get a feel if anybody has ran their fridge how long it lasts...

I typically freeze a large container full of water for my ice block, so I'm not worried about a lot of water in the bottom... just wondering how much cold leaks into the bilge.

[Stu Jackson]

1.  how long can we expect to be able to run the refer?  We've done a 3-4 day cruise with no issues... I typically run the motor for about an hour every day to heat up the water and shower.  I'm guessing I never put back everything I take out... but it lasts.  As far as regular DC load, we have the stereo (JVC car stereo), freshwater pump, cabin lights are all LED, anchor light is not on the DC system.

2.  Our refer has a drain in the bottom... is it worth covering that to keep cold air in?  I usually put a big block of ice in the bottom to help lower the load on the DC system... any other tricks?  Put a blanket over the top?  

3.  Also did anybody ever come up with a better ice trays than those vertical aluminum things that don't like to hand over the ice once they're frozen?

1.  2 golf carts give you 225 ah house bank, half that useable. I recently posted about energy budgets and doing the math.  Try this:  http://c34.org/bbs/index.php/topic,6353.msg41471.html#msg41471   That gives you one day plus @ 100ah/day without having to use the engine.  When we did a trip like that in 2004, I shut the fridge down at night and covered the top with a wet towel.  Worked just fine, extended the battery bank (ours is and was 360 ah).  Your OEM alternator should do well to recharge your house bank between the 50% and 85% SOC, and the battery acceptance will govern.  You'll only see 25 amps or less if you're doing engine runs at anchor, you need to motor somewhere at cruising speed to get the most out of the alternator.  On that trip we had the OEM alternator but also an AutoMac (and old style manual voltage regulator), so we got more out of our alternator.  Worked for us. Try this, reply #1 http://c34.org/bbs/index.php/topic,5599.0.html  {added:  the firdge draws 60 ah a day:  5A X 50% duty cycle (with a cold fridge box) X 24 hrs/day

2.  Damn right, close it up.  Hot air rises...  

3.  Patience.      It's actually quite a nifty design.  Just don't compare it to the plastic quick pop-out ones you use at home.  Ron's right.  Take it out 20 minutes before you need it, or run hot water over it.  Then take the BIG cubes out of it, enjoy having to use only one HUGE cube per drink, and store the rest in a zip lock bag in the evaporator for later or tomorrow (or breakfast ).  Refill the tray with water and replace for freezing again.  Trying to reuse the tray until it's empty is frustrating, so empty it, store the icebergs, and refreeze a new one.  Your boat, your choice.

Disclaimer:  No attempt at humor has been employed in the creation of this answer.

[Stu Jackson]

You can drain the 6V golf cart batteries pretty low can't you?  Isn't that why they're better than 12V?  

just wondering how much cold leaks into the bilge.

No, no, no.  It's a lead acid wet cell battery.  That's not why they're better.  Please don't.  Guess you don't have a battery monitor either.

All of it. That's why it should be plugged.  You wouldn't leave your fridge door open at home, would you?

[Tom Clay]

Noworries,

Our boat has the original 4D batteries from the factory, 320 amp hours in the house bank,. We have done 2 trips similar to what you are anticipating (one 10 days and the other 17 days) and found that the stock alternator kept up with our use as long as we moved (motored) every 2-3 days. We have full electronics, refrig, LED lighting, CD etc. The batteries never got below 50%, and as Stu mentions would charge to 80-85% within 2-3 hours. .

With what you have for a battery bank (225 amp hours) you are going have to really manage your electrical usage or motor every 1-2 days. I would not recommend you pull your batteries below 40-50% of capacity or you will start to reduce their life. Adding a couple more golf cart batteries should give you ample power for a 3-4 day stretch depending on use, and would be a very good idea if you will be doing more extended cruising.

Stu mentions a battery monitor, I would highly recommend as a minimum a gauge that shows percentage of battery voltage left.

Enjoy the cruise......

[2ndwish]

Stu- You mentioned that you actually need to move the boat to get the full charge current from the alternator. I'm confused by this. It seems to me that the alternator only has the engine belt speed as a variable. If the engine is running at a fixed RPM, the charge rate must be limited by that. If the charge load is increased, the engine will work harder to maintain fixed speed or may slow down. But at a fixed RPM isn't the available charge rate independent of vessel motion? Is the limitation that it is bad for the engine to run at high RPM under low load?

Also on our boat, the drain does not go straight to the bilge but to a pump. The pump prevents free flow of air to the bilge and the hose size limits the formation of convective cells.  In that case the thermal leak is limited to the increased conductivity of the small area of the hole and may not be a big leak. If the drain passes directly to the bilge, air will flow freely from the icebox to the bilge under gravity, being replaced by cooling cabin air, representing a substantial leak.

On a related thread.. we recently found that the top of the ice box was cold and noticed separation between the lid insulation and the and the lid. We removed the insulation and found it was reasonably saturated with water and ice. We dried it out and sealed the exposed foam before reinstalling.

T
 

[Stu Jackson]

Stu- You mentioned that you actually need to move the boat to get the full charge current from the alternator. I'm confused by this. It seems to me that the alternator only has the engine belt speed as a variable. If the engine is running at a fixed RPM, the charge rate must be limited by that. If the charge load is increased, the engine will work harder to maintain fixed speed or may slow down. But at a fixed RPM isn't the available charge rate independent of vessel motion? Is the limitation that it is bad for the engine to run at high RPM under low load?
 

Move boat = running engine at cruising speed, say 2500 engine rpm

Boat at idle = 1200 to 1500 rpm

Slower rpm means less rpm at the alternator and the belt moves slower and the alternator puts out less amps

You shouldn't run your engine at 2500 rpm in neutral.

Is the limitation that it is bad for the engine to run at high RPM under low load?

Yup.

Maybe I've been missing things for years.  Have folks actually been running their engines in neutral at anchor for an hour or more at 2500 rpm?  Maybe that's why they get hot water...

[2ndwish]

We cruise at ~2000 rpm at 5- 5.5 knots. Charge the batteries at ~ 1800 rpm. Either way the engine temperature is ~160-165 degrees.
While I understand that diesels prefer to run under load, what is the negative impact of running it at 1800 rpm under alternator load (for a few hours at a time)?

ps . Just consulted Calder on this- The issue comes up in two places. He recognizes it is common practice to see engines running near idle for hours at a time saying in the long run it is bad for the engine and should be minimized by using a high output alternator. Earlier he describes how the inefficient low load/low rpm running ultimately leads to carbon buildup.  What is unclear to me is how serious a problem this is for occasional cruising and given that the engine is used under load at high RPM much of the time. Nowhere could I find what an "acceptable" charging idle speed is.  In my sailing training, I was taught to run the engine for >1 hr /day at >1800 rpm while cruising-even at anchor.

[RV61]

Some thoughts,

Take a portable generator and run it an hour or two a day to recharge is possible option.

We don't put a lot food  in the freezer but do put water bottles in and when frozen scatter the bottles in the fridge.

You could add insulation around the box to aid in efficiency. I remember reading about that on the board 

We chartered a boat in BVIs 7 days and ran engine a 1800 to 2000 RPM every AM and  evening for an hour (not sure the battery pack or the alternator size) and had all usual electronic usage and 2 refers and never had an issue.

[Stu Jackson]

In my sailing training, I was taught to run the engine for >1 hr /day at >1800 rpm while cruising-even at anchor.

Well, the whole idea is to minimize the run time of your very expensive engine under an essentially no propulsion load, as compared to only an alternator/charging load.

The subject was discussed in the links I provided earlier (reply #3, end of paragraph 1):  an energy budget will determine when you need to run the engine, not to do so "blindly" for an hour a day "whether you need to or not," unless I'm misinterpreting what you wrote.  A large-as-you-can-make-it house bank will simply extend the amount of time you can go with recharging (however you choose to do so) - engine: least preferred 'cuz of the use of a relatively big diesel for a small load; generator: good alternate; solar or wind power.

Does that answer your question?

Charter boats are different.  First, they're not YOUR boat or engine; next, they get a lot of abuse; third, they don't have large house banks; last, it's easy to tell charterers to run the engine for an hour every day - simple.  'Nuther reason to seriously question buying a "retiring" charter boat.

[RV61]

Stu,
Good point on the charter boats as I not thought it out from that angle..

[noworries]

My refer has foam insulation around it, as seen from the hatch below the sink.  There is a hose that comes off the drain but I'm pretty sure it just drains to the bilge.  I never checked it, I know there's no pump, but maybe there's a valve. Will have to look.

I'm not sure what kind of alternator I have.  It does not look original.  Our boat has a M35.  On day #2 when I start the motor on the engine bank, then switch over to the house bank, and I can hear the engine take up a load. 

[Ron Hill]

No : Origionally your boat should have come with a Whale foot pump attached to the fridge drain.  Then it "T'd" into the sink drain. 

If your drain does empty literally into the bilge then I'd put a drain valve on it so you could open and close it.  Then the "cold air" wouldn't fall out!

With no battery monitor you'll still need to get an idea of your house bank status.  To do that the battery bank need to be in a steady state - no charge or discharge for about 30 minutes. 
Then check the steady state Voltage.  Use the following readings :

12.75V = 100% charge
12.65   = 90%
12.55   = 80%
12.45   = 70%
12.35   = 60%
12.25   = 50%

As mentioned you get the best longevity out of your deep cycle batteries if you recharge at 50% and don't let them get below 50% charge. 
 

[tonywright]

I was on a charter boat (twin engine catamaran) last January that had the "run the engine at 2000RPM" for 1 hour AM and PM regime. I have never seen engine oil that looked so black.

That's why I use the Honda generator for an hour instead when at anchor.  Defintely saves the engine, and cuts down on the noise as well.

Tony