Isotherm fridge

[Ketcham]

Angel,

I spoke with my brother who is an engineer. I guess the new high end inverters are very effecient. In other words, little energy is lost to heat when you convert from 12V to AC and then back to the DC use of the refrigerator. However, the ASU will not initiate during the time the inverter is on. Depending how long you have your inverter on, you may consider a switch either to the outlet or inline to the fridge. If the inverter is on briefly, to heat a meal, I would not bother.

I opted for the stove over the microwave.

[Scalf77]

Well, no matter how efficient your inverter is your still waisting battery power through the conversion. In this case your doing it twice, once to invert from 12 volts to AC and then your new converter is going from AC to 12 volts. If you use your inverter a lot while dry camping it would be worth making the AC input to your fridge switchable.

-greg

[daveb]

Most refrigerators SMB installs are 12/110. The way I understand it is if the refrigerator senses 110, it switches to the AC mode which is more efficient mode when running the refer. But with an inverter on, the inverter conversion process itself sucks all the efficiency that the refrigerator supplies @ 110AC, so you actually loose more power off the house system with the inverter on. To add to insult, when you turn on the inverter, it powers all the plugs including the microwave which lights up. The problem is there is no dedicated AC circuit to the refrigerator which can be opened at a breaker. At least that’s how mine is wired. So when I use my microwave, my refrigerator switches over to AC and runs off the inverter….this sucks unless I’m on shore power. I would like to be able to keep the refrigerator off the AC mode in the field (on DC mode) by a switch/breaker while the inverter is on.

This might not be how the Iso-Therm works.

[Ford_6L_E350]

As much as I hate to disagree with Dave, I don't believe the 110AC function of the refrig is more efficient. The assumption is the AC is from shore power and nearly unlimited capacity compared to the battery - hence it defaults to shore power when available.

Inverters really confuse the issue. When running off an inverter the AC power is more limited than the battery power (same source, losses in both conversions DC-AC and back).

Really you need an AC outlet that is only powered from shore power and isolated from the inverter for the refrig plug. Or, leave the refrig unplugged and let the batteries power the refrig all the time. Shore power will charge the batteries if you are plugged in, so no problem there.

Mike

[daveb]

Mike, you don't think the refrigerator cools better in the AC mode?

I'm just going on what SMB claimed. Very possible they were referring to loosing battery power but SMB told me the units cool better when running off AC power. Now I wonder if that's true. One of the earlier post said that Jonathon claimed they don’t sell 12/110 units anymore. What has changed in the models? Mine is what they refer to as a 2-way refrigerator. I’ve always assumed the compressor is 110. I do plug into shore power to keep the batteries from over cycling at night while at home.
Trying to get information out of anybody about these refrigerators is like pulling a tooth out of a kids mouth. I've got a good friend who works on these things...maybe he can shed some light on the subject.

[jage]

I did this as part of my fridge project:
viewtopic.php?f=13&t=487&p=2840&hilit=switch+110#p 2840

[Ford_6L_E350]

Dave,

My refrig has a 12V compressor and needs a power supply for running on AC. And that makes alot of sense, more than having an AC compressor and an AC synthesizer for running on batteries.

Mike

[daveb]

Thanks for clearing that up Mike I never knew exactly how they operated. I always assumed there was an AC compressor. I was told some don’t even have a compressor but some kind of freezing plate.

In the field SMB stated that I should turn off the breaker going to the refrigerator to keep it on 12v mode when using the inverter because it (the refrigerator) will sense AC available and draw from the inverter increasing load. I was told on shore power the inverter is bypassed and the fridge is also bypassed off the 12v house system to shore power. If so, they seem to be correct. Because there is a 12 volt input (and 12v compressor), it makes no sense to let the inverter convert 12 to 110 then take 110 in the fridge and drop it back down to 12v. What I was saying about the dedicated 110 circuit is that when I use my inverter, the fridge switches to it as well and I’d rather keep it on the 12 volt side by opening a breaker.

It’s still a wild guess on my part, but I resist keeping the charger on 24-7 while on shore power. Because the batteries are heat sensitive, the charger does seem to shut down when it’s hot outside, common in the summer where I live. There are times when charging an AGM is not advised and fairly sure one time is when the battery temp reaches a specific temperature. Also I have yet to fully understand how my Prosine supplies its smart charge. I’ve noticed (on mine) while on charge, it seems to reach a point and than shuts down to a float mode. During the night, the refrigerator cycles on and off and at least in my case, the inverter appears to stay in the float mode. The house batteries are depleted to a point around 12.5. Before the sun comes up and the solar kicks in, I can go out and restart the charger where it will kick back into a higher charge state and I read a good 9 amps or so charge going to the batteries. It’s a fairly quick charge but I prefer to not cycle the batteries while the van is sitting on the driveway. Solar keeps everything topped off during daylight and at night the batteries sit static with no use because I’m plugged into shore power to run the fridge. This all came up when trying to figure out why Angel’s batteries went flat in only a couple of years. She might have just had a battery fail, so time will tell if she sticks with the same procedure. Also I don’t know how different inverters charge or how the Isotherm works so it’s kind of a guessing game when dealing with different setups.

Does this seem correct?

[Ford_6L_E350]

With your solar power and plenty of daylight, why do you feel the need to plug in at night? We go camping for weeks at a time, solar during the day, refrig running all day and night, batteries are usually around 12.2V in the morning. Solar brings them up to 12.6V in short order. A little load on a battery won't hurt it.

Mike

[daveb]

Originally Posted by Ford_6L_E350

With your solar power and plenty of daylight, why do you feel the need to plug in at night? We go camping for weeks at a time, solar during the day, refrig running all day and night, batteries are usually around 12.2V in the morning. Solar brings them up to 12.6V in short order. A little load on a battery won't hurt it.

Mike

Because most AGM batteries companies suggest that constant or over cycling of the batteries is a negative thing and will shorten the batteries life. At 3-400 bucks a pop I’m a bit concerned with that. They suggest taking the batteries down no lower than 50% then bring them back to 100% within a couple of weeks. I could be wrong but here is what I see that is considered improper battery usage is from worst to best:
1. Taking your batteries to well below 50% and letting them sit for over a month without any charging.

2. The same as above but between 50 and 90%.

3. Taking your batteries down to below 50% constantly but applying a correct charge afterward.

4. Again, same as above but between 50 and 100%. This is normal usage and what I try for in the field. An Alternator will bring the battery back to about 90% but solar will top it off to 100% and is a good thing. People W/O solar should consider this.

5. Keeping the batteries at no lower than 60% or more during usage and returning them to 100% ASAP.

6. Cycling the batteries as little as possible (usage the lowest % possible) and returning them to 100% ASAP.

7. Never using the batteries and keep them at 100%. Actually I’m not too sure about this because there is some discussion about exercising batteries but the engineer from Concord is where I got some of this info. He said it’s not necessary to exercise an AGM battery. Obviously nobody purchases a battery and lets it sit with a light charge never to be used so it’s N/A.

There are no problems with letting AGM batteries sit without load for up to a month without charging. I’m just saying why cycle the batteries unless you are out in the field and doing what they are made for? I don’t have a problem when camping. It’s at night especially during summer when the heat is on and the fridge is on and off constantly throughout the night while sitting on my driveway. I have a nasty habit of leaving my fridge stocked ready to head to the hills and my charger seems to let them drop to like 70% by morning. Maybe it has to do with me never turning off my fridge? I’ve had my batteries for several years now and they still have a good resting voltage of 12.8. I’m sure that will change with age.

I’m far from any kind of expert on this but have discussed it with a few who supposable knew what they were talking about and have read up a bit on the issue. A little knowledge can make someone like me look like an idiot but discussion is good and what makes this forum excel. I could be getting poor info or not taking it in correctly. I remember when I read several wet cell battery articles about how to treat my bass boat batteries years ago. Later I found out most of those articles were….well full of it. Sorry if I’m going techno ballistic here.

DaveB