Where to put the refrigerator compressor? & Battery Float Discussion

[Dancrosswis]

Hmm.  I'm back again after reading John Nixon's message on battery chargers.  He seems to squarely address my situation.  I'll quote the relevant parts of his post:

First, let me say that I am a mixed-bagger: I keep ( for the last 20-ish years) AC power on the boat 24/7 to keep the beer cold, and to keep the inside temperature of the boat reasonable with my wonderful 16,000 btu of reverse cycle air-conditioning.
...
All battery do not like having residual charge current flowing through their plates for extended periods of time. However, for our discussion here, I'll limit my comments in particular to deep cycle lead acid batteries. As Stu accurately quoted some of our direct correspondence, the problem created by continuous charge/residual current flow through lead acid batteries in positive grid corrosion.
...
The stated 35 to 40% maximum reduction in useful life of a deep cycle lead acid battery due to continuous float charging was based upon Concorde's own testing and their experiences in field applications...
...
So, if 24/7 float charge is bad, what to do about 12 volt refrigeration ( i.e. - your Cold Machine )? The simple answer is to provide a suitable AC-to-DC power supply to run the fridge when you are at the dock, and then run it on the batteries when away from AC power. I have been doing this since 2002. There are a number of inexpensive and suitably reliable small switching power supplies out there that will do the task admirably.

John Nixon at http://c34.org/bbs/index.php/topic,4352.0.html.  (Emphasis mine).

I guess I'm going to flip flop and install the MPS-35. 

Regards,

Dan

[J_Sail]

There are two separate issues being conflated here.
1) Your originally stated worry that running the fridge from your boat's 12v system while on the charger is bad for the batteries because it places a load on them.

2) John Nixon's statement that leaving your battery charger on 24x7 is bad for the batteries due to the small charging current created by the float voltage it applies.

#1 is a misplaced worry, as I explained in my previous reply. There is no load on your batteries when they are on the charger; the needed current comes from the charger.

#2 is a theory that I do not see espoused by leading experts in the field. I have not seen the study and research that John referred to. The leading expert in the yachting community seems to be Rod at Compass Marine (aka MaineSail) and his articles on selecting and setting up marine battery chargers and his extensive writings on caring for marine batteries do not mention it. My understanding is that the general consensus is that if one sets a quality modern marine battery charger to the float voltage recommended by the battery manufacturer, it is fine to leave it on the charger 24x7. It is true that many years ago it was not uncommon to find battery chargers with wildly incorrect float voltages, and too high a float voltage can shorten battery life. In my professional field (I am an electronics engineer) I have seen that problem with some computer UPS units that had float set too high, but not in any modern marine setups I have worked on.

You are making your setup more complicated, so I suggest you consider the extra complexity and the uncertainty surrounding any potential benefit before pulling the trigger.

IMPORTANT - Regardless of how you view the above, there are two problems with your plan that must be addressed.
1) If you are going to use a small DC power supply to run the fridge while on shore power, it should output 12-14vdc, not 24-27vdc. The unit you linked to says it outputs 24 or 27v. Hopefully it can be set to 12-14v, or it won't be right for your 12v fridge.
By the way, is it a MPS-35, MPS-50 or MPS-150? I think you have referred to it as all three at various points in your thread.

2) You will need a relay and additional wiring if you want the fridge to automatically switchover from your boat's 12v system to the separate power supply. That function is not built into the devices you have bought.

[Stu Jackson]

One of our skippers did a  much simpler thing to address the issue you claim to face.  He installed a small 12V battery (in his nav station locker) and tied it to a relay, such that when he turned off his main 1-2-B switch, the fridge ran on the small battery only, bypassing his main house bank.  If his small battery died, it was almost no cost to replace it.

I agree with Jeremy, you're really over complicating this.  You might consider sending a pm to John Nixon and asking him, since that charger thread is very old.

[Craig Illman]

If you're really concerned about having the batteries on float continuously, the Sterling Procharge Ultra (ProMariner ProNautic) can run in power supply mode without a battery attached.

Craig

[Dancrosswis]

Thanks for all of the great input.  I appreciate everyone's efforts. 

J_Sail.   Thanks for clearly setting out this unfolding discussion.

Issue #1.  You've got me convinced that there's no load on my battery to run the refrigerator when the charger is working. 

Issue #2:  On the second issue, which could be generalized as "is my float charge harming my batteries", I think I'll follow Stu's advice and contact John for an update.  I've also emailed Interstate for their recommended float voltage for my SRM-27's and to ask them whether my charger's' (Xantrex Truecharge 20+) float voltage of 13.5v can harm the batteries.

MPS-35.  Well, I never called it a MPS-50.   And, I only called it a MPS-150 once, before I wised up.  It is a MPS-35, designed for the Danfoss BD35F compressors.  Those compressors operate on either 12v or 24v, so my (limited) understanding is that the compressor will run fine on the MPS-35's 24v output voltage.  The MPS-35 has automatic power source switching (from AC to DC) built in.  No additional relay is needed.  The attraction of the MPS-35 was that it looked to be mostly plug and play.  But, if I don't need it to help my batteries--then I don't need it.

Stu.  I'll follow your suggestion to contact John.  And, thanks for passing along the other solution.

Craig.  Thanks for the suggestion.

I'll send additional information and results as I go along.

Regards,
Dan Cross
Ennui Went
1986 C34 #159

PS  Got sidetracked the last couple of days.  My bilge float switch died, which led to my first contact with my bilge pump wiring.  Yikes.  The pump runs off an "Auto-Off-Man" panel switch.  I've got an older Rule 3700 that draws from 15A-20A.  The wire run is about 20 feet. My iPhone app says ABYC demands 8AWG for less than 3% voltage drop.  The wire I pulled was about 18AWG at the panel switch, had two unprotected butt splices (no shrink tubing, tape, liquid tape... no nothing) at the bottom of the bilge, stepping down to 22AWG single strand.  All unfused.  I think I read that electric bilge pumps were an option in the early 34s.  This didn't look like a factory installation.

[Noah]

Not to side track you further, but make sure your bilge pump is wired with constant power direct from the battery (and properly fused), bypassing your main DC house bank battery switch--so it (and your float switch) stay powered when you power down your main panel.

[Dancrosswis]

Good advice Noah.  All done.

[mainesail]

Guys,

Float charging in a marine application is not the Devil here, and certainly arguably may not warrant a stand alone power supply or the complexities that go along with them.

Even battery engineers disagree on the topic of floating. The inventor of the Firefly, a fellow Mainer who's brain I get to pick pretty regularly, prefers these batteries to ideally not be floated. He agrees though that they have to be, in the real world, due to parasitic loads etc.. His compromise is a float of 13.2V. Only recently has he very, very reluctantly said 13.4V was okay. He has only done this because knuckleheads spent $500.00 per battery but were then too cheap to buy a proper charger. They then complain on-line about the "Odd and very low Firefly float voltage". yet another case where the average Joe consumer knows more than the inventor of the product so the manufacturer is forced to adapt to something they actually disagree with... D'oh....

Kurt still stands firm in his no-float as the best practice and 13.2V if you really have to, and 13.4V for knuckleheads who refuse to buy the correct charger. (grin) The Firefly is a prime example of a battery not designed for UPS type float service, it was designed for active cycling and floating it serves no real benefit unless you have parasitic loads like most boats do then it is more of a necessity than doing any actual good for the battery.

Float charging can cause grid corrosion, and is a higher risk in VRLA than it is in flooded batteries due to the recombination process creating excess heat. Despite this your batteries placed in 100% float time service, think emergency UPS back up type use, would still outlast perhaps 99.99% of the batteries used in a PSOC deep-cycle manner in the marine space. In other words your biggest enemy is not floating it is deep-cycling, crappy chargers, non-temp compensated charging, chronic undercharging, dock side power losses with DC loads running, PSOC use etc. etc. etc....

What is damaging & bad about "floating" is that very few marine chargers can hold a continual float during refrigeration compressor cycling. This is causing the charger to switch back and forth between a float level voltage and absorption level. Poor chargers with high ripple are also damaging especially to VRLA batteries. Also very damaging is the use of a non temp compensated charger that lacks an on-battery temp sensor. The solution to prevent reverting to absorption, from always on loads, is to simply create a charge profile for dockside charging with it set for only float level voltages at just a tick over resting voltages such as 13.2V. Charge to 100% SOC and then switch to "forced float" or simply turn off the DC loads......

Most "marine" chargers out there SUCK DONKEY BALLS. There is no perfect marine battery charger, it has not yet been built, so be sure you buy one that has a forced-float feature/switch or one that you can custom program to remain in float while dockside, if you really must run dock side DC loads. Forcing the charger to stay in float will not allow compressor start up to launch the charger back to absorption multiple times per day.

It is fairly well known that I am not a proponent of shore side charging & always-on dock side loads, for any reason, and I like cold beer like everyone else. I see FAR, FAR, FAR too many destroyed banks due to charger failures and AC power interruptions, on the order of about 15k in ruined batteries yearly due to shore power interruptions & DC loads left on. In contrast I have seen none destroyed by loss of power who run solar instead of plugging into shore power... Shore charging with always on loads are simply a risky practice.

I generally prefer to maintain the batteries unplugged from shore and using solar. Last time I checked the sun has not been interrupted for millions of years yet dock side power is routinely interrupted. Once the batteries are full it takes very, very little sun to maintain them and even in pouring rain there will be sufficient charge to maintain them.

Plugging into shore power without a properly wired isolation transformer is simply a risky practice too and NO a galvanic isolator is not the same as an isolation transformer.. Even with an isolation transformer leaving loads running leaves you with the potential to MURDER your bank when the power goes out, which it does on docks with surprising regularity.

If you really must leave DC components running when dock side:

#1 Use the smallest current charger you can to maintain the DC loads and battery. It should be able to be "forced to float" with no way to revert to absorption.

#2 Install a DC low voltage cut off/disconnect set to at least 12.1V for the "always on loads".

#3 Install a properly wired isolation transformer.

#4 Consider using your "cheap" starter/reserve battery as the DC buffer/float power instead of an expensive house bank. It should have it's own charger if you do this not just one leg of a charger..

[J_Sail]

Thanks for all of the great input.  I appreciate everyone's efforts. 
...
MPS-35.  Well, I never called it a MPS-50.   And, I only called it a MPS-150 once, before I wised up.  It is a MPS-35, designed for the Danfoss BD35F compressors.  Those compressors operate on either 12v or 24v, so my (limited) understanding is that the compressor will run fine on the MPS-35's 24v output voltage.  The MPS-35 has automatic power source switching (from AC to DC) built in.  No additional relay is needed.  The attraction of the MPS-35 was that it looked to be mostly plug and play.  But, if I don't need it to help my batteries--then I don't need it.

I mentioned the MPS-50 because the link you included took me to a page on the MPS-50, thus I asked about all three possible P/N's. As it turns out, though, it looks like the MPS-50 is just a slightly more powerful version of the MPS-35. More importantly, you are correct that the MPS does indeed include the relay built-in. I finally found the instruction manual online. Also, you are correct that the fridge compressor will auto-switch dynamically between 12v and 24v operation (I was concerned that it had to be pre-set to either 12v or 24v). So, it appears you could fairly easily add the MPS-35 to your setup.

As MaineSail correctly noted, it is true that some battery chargers will react to the on/off load of the fridge by invoking a higher-voltage charge cycle for some period of time. It looks like the Xantrex you have checks the battery voltage every 15 minutes, so hopefully that would limit the duration of any mis-provoked charge cycle. So, it's unclear if the potential benefit outweighs the extra complexity; you could go either way and someone will disagree!

As to proper float voltage, according to the manual I looked at, you can influence the profile by both selecting the battery type and the temperature setting (if you don't have the optional Battery Temp Sensor). Normally I would recommend the Batt Temp Sensor option, but I suppose it is conceivable you could instead set the temperature switch to HOT on the charger panel and get reduced float voltage at the expense of slower charging. That *might* make sense if your boat sits on the charger 24x7 with short sailing periods and the batteries rarely get run down much. (Caveat, I have not looked carefully at the numbers, so take with a grain of salt). As to which battery profile to pick, as MaineSail has said elsewhere, look at the voltages in the spec sheet for each profile and compare them to the specs of your specific batteries rather than assuming the names the charger manufacturer called them make sense. In your case, since Interstate is a re-labeler rather than a manufacturer it may be harder to get precise battery specs.
Your charger sounds like this one:
http://www.xantrex.com/documents/Discontinued-Products/TC20_40(445-0050-01-01_Rev-A).pdf
Look at the sections on Battery Temperature and the profile definitions in the Specs section.

[crieders]

I put my unit under the rear lazarette too. How often do folks re charge it? Mine has been in quite a while

[Noah]

Cliff, how old is your reefer? If it is the "original" 1990 vintage compressor, recharging is an expensive operation. It uses the EPA banned R12 Freon, which is hard to get and expensive when you find it. Also, the system is sealed and the refrigerant lines will need to be tapped with a special fitting in order to charge.

[Stu Jackson]

>>>>>>>>>>>>>>
How often do folks re charge it?

Cliff, mine's been in since 1986 and is still working, I did have to replace the electronic module in 2016.  Do a search on "rParts" for the details.

There is NO "how often" to this system.  It's like asking how long did your freshwater pump, raw water pump, domestic water pump, water heater, macerator pump, shower sump pump or last wife last?!? 

I could tell you how long mine have, but your experiences are guaranteed to be different.  I have an "ancient" boat, but with due diligence and USE, I have been blessed by having stuff continue to work.  Jon W recently posted his list of repairs he did on his boat, a few years newer than mine.  While he'd be welcome to do that work on my boat, it wasn't needed.   

I did replace our water heater in 2013, detailed in a tech note in 2104.  They last 12-16 years.  My PO did a new one before we bought his 12 year old boat in 1998. Run the hot water even if you don't have hot water to keep it moving through the coil and it will last longer.  Our dock mates have a beautiful Island Packet, but they had this incomprehensible aversion to using the built in hot water system on their boat.  Ever. They use a Solar shower at their dock!!!    Crazy.  They are replacing their heater, although it is 16 years old.  Your boat, your choice.     But there are tips and techniques we've been sharing for decades.

Cliff, how old is your reefer? If it is the "original" 1990 vintage compressor, recharging is an expensive operation. It uses the EPA banned R12 Freon, which is hard to get and expensive when you find it. Also, the system is sealed and the refrigerant lines will need to be tapped with a special fitting in order to charge.

Noah is quite right.  Reason is the old system did NOT have Schrader valves on the refrigerant lines.  This may well be why my system had no leaks, dunno.  The Schrader valves allow re-topping with refrigerant without disassembling the connectors.  Somehow the logic of the "damned environmentalists" escaped me:  they wouldn't allow Schrader valves on the older units to avoid contaminating the ozone layer, but would on the newer units.  Ken Heyman got an R12 certification and he and former C34IA Commodore Bob Kuba recharged their system a few years ago, on their 1988 and 1990 boats.  IIRC, Ken did quite a good writeup of it right here on the forum.  I'll leave it to you to do the search work.

[Hugh17]

Hi,
My compressor is located under the stove.  By previous PO.
Might not be ideal, but works.
Pretty close to box.  No venting issue.  I made a small panel to cover the area with vent slot.
It is not close to the berts, so it does not disturb at night.

Do you have a picture? What unit? I'm considering this type replacement.
Thanks