Hi all, I am about to try a gas saving trick with my Dometic 3 way fridge. I want to turn the gas off through the day and run my 3000 w inverter to power the the fridge on AC.
Then at night go back to gas.
Has anyone had any success with this technique?
T1 Terry said
12:02 PM Sep 25, 2019
You need a lot of solar. We have a few customers that have done that in the past, but they have all upgraded to a household 240vac fridge since so it can run 24/7 from the dedicated inverter that powers it. This method uses less than an a 12v/24v RV fridge, works better and they already have that much solar from running the 3 way fridge they have enough spare to power the hot water instead.
T1 Terry
Dolly said
04:17 PM Sep 25, 2019
Thanks Terry, Ive heard that the 12v element uses more power than the 240v which apparently only uses 120w ...... unless they are one in the same. I have 2 x 200w solar and 300 ah battery
running a 3000w inverter.
blaze said
04:34 PM Sep 25, 2019
When I brought my coaster it had a small 3 way fridge (probably 40l) and it was run solely on 240v via an inverter, had no gas or 12 volt hooked up when I pulled it out. It had 1 house battery of 100ah which was charged via a 24v to 12 v charger. The previous owner told me she only run it whilst driving and for short periods when stopped.
cheers
blaze
T1 Terry said
05:06 PM Sep 25, 2019
Dolly wrote:
Thanks Terry, Ive heard that the 12v element uses more power than the 240v which apparently only uses 120w ...... unless they are one in the same. I have 2 x 200w solar and 300 ah battery running a 3000w inverter.
Add the inverter losses and they will be savage on a 3000w inverter powering a 120w load. If it is 120w @ 230v then the 230v load is only around 1.9 amps. The standby current for those 3000/9000w inverters can be as high as 3 amps @ 12v and the 1.9v @230vac would be enough to hold it in running mode. 120w @ 12v is 10 amps + the 3 amps stand by current = 13 amps. You should get around 23 amps out of the solar in good solar weather, so that leaves 10 amps to power all the other loads as well as recharge the battery.
If you have a Victron BMV you will be able to see what the real load is by turning the inverter off and reading the solar charging, then turn it on and see how much is left going into the battery to recover last nights use. That will give you a good indication as to whether you can do it or not, but 400w is getting close on the borderline as far as solar goes. You don't want to be using any out of the battery while the solar is charging, this is the period where it should be putting it back in not drawing more out.
One advantage you may have, I believe the 240v side is thermostat controlled, so maybe it will not be drawing power full time. Unfortunately the inverter will so that maybe 3 amp loss will be constant.
If you have a top of the range inverter, then it might not waste that much on standby, but only a battery monitor will really tell you that.
T1 Terry
Dolly said
05:15 PM Sep 25, 2019
Thanks again Terry, youve given me a lot think about.....starting to think Samsung now and run 2 more solar with seperate batteries and inverter.
Dont you just love the challenges of being a Nomad
Jaahn said
05:38 PM Sep 25, 2019
Hi Dolly
Terry has probably covered most things to say about 240V use. My only comment would be why do people buy such big cheap inverters. If you bought a better smaller one that is matched to the load and has a standby mode it might avoid a lot of the wasted power.
But i was going to say why not just use the 12V element on the 3 way while on solar. The inefficiencies should be less as there is no conversions to be done. I found they work OK when the voltage is up to charging voltage on solar. The current is high but not as bad as the inverter uses. You should put much bigger wires on it from the battery also which helps a lot. That transformed my old previous one.
Jaahn
-- Edited by Jaahn on Wednesday 25th of September 2019 05:45:19 PM
Bagmaker said
05:59 PM Sep 25, 2019
Jaaan, the only time you have too much power is when you're being electrocuted. The wife, for example, has no compunction when turning the microwave on whilst the A/C is running and the fridge is running and the freezer is due to cut in. She will not think twice about firing up a hair dryer directly afterwards, unless scorned prior.
You are right on the cheap ones though, one gets what one pays for (- says this one, about to upgrade )
The best way to fix a 3 way fridge is drill a small hole about 50mm from the rear, on top, and about 80mm from one side (preferably the side away from the chimney) The hole should be about 12-13mm dia, max you can get with a standard battery drill. Drill it through as far as possible, until fresh air is met. Run some heavy wire or chain through the hole and form a strong loop. This makes a handy point to attach an anchor chain for a small boat, the door should be removed first in case it comes free and floats away. Replace it with a decent, modern compressor fridge, inverter controlled if you have the room.
People will try and tell us how good an aircooled VW engine is but seldom compare it to a modern watercooled porsche engine.
T1 Terry said
12:44 PM Sep 26, 2019
Bagmaker wrote:
Jaaan, the only time you have too much power is when you're being electrocuted. The wife, for example, has no compunction when turning the microwave on whilst the A/C is running and the fridge is running and the freezer is due to cut in. She will not think twice about firing up a hair dryer directly afterwards, unless scorned prior.
You are right on the cheap ones though, one gets what one pays for (- says this one, about to upgrade )
The best way to fix a 3 way fridge is drill a small hole about 50mm from the rear, on top, and about 80mm from one side (preferably the side away from the chimney) The hole should be about 12-13mm dia, max you can get with a standard battery drill. Drill it through as far as possible, until fresh air is met. Run some heavy wire or chain through the hole and form a strong loop. This makes a handy point to attach an anchor chain for a small boat, the door should be removed first in case it comes free and floats away. Replace it with a decent, modern compressor fridge, inverter controlled if you have the room.
People will try and tell us how good an aircooled VW engine is but seldom compare it to a modern watercooled porsche engine.
:lol: love it. You are right about trying to run small loads with a power hungry cheap large inverter, but they all have their place. A household fridge on the market today will run happily from a 375 Victron inverter and can be left on 24/7 with a second lead to charge the computer/mobile phone. Only turn the big power hungry unit on when the big loads are required and turn it off when they are no longer in use.
Another method is to use a Projecta IP2000 to run the fridge, small kitchen appliances, the washing machine and what ever else won't exceed the 2000w limit for too long if somehow they all got turned on at once. It will scream at the operator if they attempt to over load it but as long as the over load isn't more than 20% it will carry it for a while, like a 2400w kettle will actually boil the water but you have a migraine from the inverter complaining before the kettle boils. The roof top rattler will run on an IP2000 where it won't run on a Honda Ei2.0 unless you use that ridiculously short lead and have the generator right beside the van, that changings things from hot and bothered to either hot or bothered, the solar/battery inverter method is quite, pity about the noise from the roof top rattler but that is just part of their design
Now if more things need to be used all at the same time, the big power hungry inverter can run the air con, the water heater, the microwave and all those other power hungry devices, just turn it on when you need it. This does involve wiring the power points into 2 separate circuits, but most big vans have that already so not that hard to do. I've set up a few this way, one has a family of 5 living in it when mum is one the teaching/training circuit, the other runs leads from their caravan to house circuits when they are home and run quite a bit of the house from the free power the caravan can supply.
It doesn't take very many mths free camping rather than paying caravan park fees to pay for itself and the freedom it gives is priceless
T1 Terry
Aus-Kiwi said
04:21 PM Sep 26, 2019
I have seperate 600 watt inverter for 240 when I have smart TV ? Etc . I guess this option
Would work on fridge too . Yes better to have inverter screaming than trying to explain power usage !
T1 Terry said
12:02 PM Sep 27, 2019
Dolly wrote:
Thanks again Terry, youve given me a lot think about.....starting to think Samsung now and run 2 more solar with seperate batteries and inverter. Dont you just love the challenges of being a Nomad
Missed answering a bit of this post. No need to separate the batteries into different packs. If you want to add more batteries then add them to the original battery pack, just make sure you wire them correctly, not just daisy chained from one to the next because this will murder the first battery in the chain and that will kill the others if not isolated quickly.
T1 Terry
cheers
blaze
Add the inverter losses and they will be savage on a 3000w inverter powering a 120w load. If it is 120w @ 230v then the 230v load is only around 1.9 amps. The standby current for those 3000/9000w inverters can be as high as 3 amps @ 12v and the 1.9v @230vac would be enough to hold it in running mode. 120w @ 12v is 10 amps + the 3 amps stand by current = 13 amps. You should get around 23 amps out of the solar in good solar weather, so that leaves 10 amps to power all the other loads as well as recharge the battery.
If you have a Victron BMV you will be able to see what the real load is by turning the inverter off and reading the solar charging, then turn it on and see how much is left going into the battery to recover last nights use. That will give you a good indication as to whether you can do it or not, but 400w is getting close on the borderline as far as solar goes. You don't want to be using any out of the battery while the solar is charging, this is the period where it should be putting it back in not drawing more out.
One advantage you may have, I believe the 240v side is thermostat controlled, so maybe it will not be drawing power full time. Unfortunately the inverter will so that maybe 3 amp loss will be constant.
If you have a top of the range inverter, then it might not waste that much on standby, but only a battery monitor will really tell you that.
T1 Terry
Hi Dolly
Terry has probably covered most things to say about 240V use. My only comment would be why do people buy such big cheap inverters. If you bought a better smaller one that is matched to the load and has a standby mode it might avoid a lot of the wasted power.
But i was going to say why not just use the 12V element on the 3 way while on solar. The inefficiencies should be less as there is no conversions to be done. I found they work OK when the voltage is up to charging voltage on solar. The current is high but not as bad as the inverter uses.
You should put much bigger wires on it from the battery also which helps a lot. That transformed my old previous one.
Jaahn
-- Edited by Jaahn on Wednesday 25th of September 2019 05:45:19 PM
Jaaan, the only time you have too much power is when you're being electrocuted.
The wife, for example, has no compunction when turning the microwave on whilst the A/C is running and the fridge is running and the freezer is due to cut in.
She will not think twice about firing up a hair dryer directly afterwards, unless scorned prior.
You are right on the cheap ones though, one gets what one pays for (- says this one, about to upgrade
)
The best way to fix a 3 way fridge is drill a small hole about 50mm from the rear, on top, and about 80mm from one side (preferably the side away from the chimney)
The hole should be about 12-13mm dia, max you can get with a standard battery drill.
Drill it through as far as possible, until fresh air is met.
Run some heavy wire or chain through the hole and form a strong loop.
This makes a handy point to attach an anchor chain for a small boat, the door should be removed first in case it comes free and floats away.
Replace it with a decent, modern compressor fridge, inverter controlled if you have the room.
People will try and tell us how good an aircooled VW engine is but seldom compare it to a modern watercooled porsche engine.
:lol: love it. You are right about trying to run small loads with a power hungry cheap large inverter, but they all have their place. A household fridge on the market today will run happily from a 375 Victron inverter and can be left on 24/7 with a second lead to charge the computer/mobile phone. Only turn the big power hungry unit on when the big loads are required and turn it off when they are no longer in use.
Another method is to use a Projecta IP2000 to run the fridge, small kitchen appliances, the washing machine and what ever else won't exceed the 2000w limit for too long if somehow they all got turned on at once. It will scream at the operator if they attempt to over load it but as long as the over load isn't more than 20% it will carry it for a while, like a 2400w kettle will actually boil the water but you have a migraine from the inverter complaining before the kettle boils. The roof top rattler will run on an IP2000 where it won't run on a Honda Ei2.0 unless you use that ridiculously short lead and have the generator right beside the van, that changings things from hot and bothered to either hot or bothered, the solar/battery inverter method is quite, pity about the noise from the roof top rattler but that is just part of their design
Now if more things need to be used all at the same time, the big power hungry inverter can run the air con, the water heater, the microwave and all those other power hungry devices, just turn it on when you need it. This does involve wiring the power points into 2 separate circuits, but most big vans have that already so not that hard to do. I've set up a few this way, one has a family of 5 living in it when mum is one the teaching/training circuit, the other runs leads from their caravan to house circuits when they are home and run quite a bit of the house from the free power the caravan can supply.
It doesn't take very many mths free camping rather than paying caravan park fees to pay for itself and the freedom it gives is priceless
T1 Terry
Would work on fridge too . Yes better to have inverter screaming than trying to explain power usage !
Missed answering a bit of this post. No need to separate the batteries into different packs. If you want to add more batteries then add them to the original battery pack, just make sure you wire them correctly, not just daisy chained from one to the next because this will murder the first battery in the chain and that will kill the others if not isolated quickly.
T1 Terry