Might as well keep the roll going and talk about how to squeeze more efficiency out of your holding plate system, since its now too hot to get in the white Tyvex suit and paint
the bottom. I'll do that this evening now.
If you can store up "Cold BTUs" in your holding plate when you have excess 12v DC power then you can use those BTUs later when your charging
source go away (alternator/wind/solar). So what are some ways to do that?
1. Old Fashioned Bigger Is Better
Bone simple takes us back to the early days of holding plate refrigeration where bigger was better in terms of holding plates, but at an increased cost and space in the box. If you increase your holding plate eutectic solution volume and are able to freeze it down during the day when you have solar/wind/alternator power to spare, then you will have less compressor cycling at night. No controls...nothing really special to do once you have installed the larger or extra holding plate volume.
2. The El Cheapo
I use the phrase fondly because I fall into this category myself. I like cheap
and I like easy, but this does put my memory to the test and some times it fails and I freeze my lettuce.
Here's how it works.
The thermostat affixed to the holding plate turns the compressor on/off based on the temperature set points and is just a simple switch that is either open and the compressor is off or closed and the compressor turns on. So you can install a bypass switch around the thermostat leads so that when you turn on the switch the compressor controller sees the "yes turn on signal" and starts up. So any time I am motoring or when my solar
controller is floating my batteries and dumping available power I turn the switch to ON and force on my compressor. This will freeze down the plate to a lower temp than "normal" and I will be able to store more "Cold BTUs" in my holding plate. So when the sun sets or alternator
turns off it will be a longer time for the 12v compressor to kick on and use battery
power to pull out heat.
The negatives of this El Cheapo Approach are:
A) if you forget to turn off the switch it can run all night because the damn things so quite you will forget it is on. (ok put a timer switch in, to prevent that, but I'm too lazy for that)
B) You run the risk of freezing your refrigerator
if using a spill over approach because you will see lower temps in your freezer spilling over and if your unit is just a refrigerator
plate, it will get much colder than the "normal" 25-degs F
3. The Tech Nerd
Come on, admit it, you know who you are and we love you but at the same time hate you for wiring
up gizmos that we can't figure out then telling us how easy it is on the chat rooms.
Here's how it works.
Take the same concept
from the El Cheapo, but rather than relying on yourself to turn a simple switch on and off, set up a voltage sensing relay to a nice full battery charge voltage...say 13.9v...and then when your battery gets to that voltage from either wind/solar/alternator the relay will close a switch and boom...the unit kicks on automatically. You would have the same negative as the El Cheapo in that on long motors or too sunny of days or on shore power
you unit won't turn off and you can freeze your beer. But a true tech nerd would also put a timer into that relay circuit to only close the switch for an hour at a time and then wait 30 minutes again before cycling on if the voltage is high enough. Heck get real cool and add an OFF function when it senses being on shore power
or make it cut off at a low temp setpoint.
4. The Money Fixes Everything Guy
For those of us that are too lazy for an on/off switch and not electrically smart enough to play electronic engineer
, there of course is the "money solves all problems" approach. SCAD makes what's called a SensiStat to optimize performance of holding plate refrigerator systems.
SensiStat | Technologies LLC
(I'm not affiliated with this in any way...but I might one day carry it as a dealer for them if I ever get around to it)
It follows the same logic as above, by turning on the unit when you have a preset and adjustable battery voltage BUT it doesn't just force the unit on and freeze your beer. It shrinks the hysteresis down to 1-deg but adds in Box and Holding plate monitoring into the equation. Plus lots of additional cool features for the money
. These babies list for $295 and from the testing I've done they do work and save you some battery power, just how much can depend on your boats energy profile. Obviously if your batteries are never at some high full charge set-point then forget it...spend the $295 on insulation
, better hatch seals
, of the famous "Beer Flywheel Affect"...ha ha