Power source selector switch

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I was not saying anybody proposed that, but a switch could allow that to happen quite easily and I think steps should happen to insure it cannot, and that a suitable delay is incurred before switching from 12 to 24vDC or back.

I've no idea the risks, but I would not assume it does not exist.
 
What steps do you think would be involved beyond:

1 Use that BS 3-position switch, and wire it so that power to the fridge and to its compressor are controlled together.

2 Pause in the OFF position for at least ten seconds when changing selected voltage

?
 
I would turn the refer off with the switch on the refer, then switch voltages, then turn the refer back on. but like I said before this comes from a lifetime of using power tools. I would never leave a power tool switch in the on position and turn it on by just plugging it in. highdesertranger
 
I'd do as HDR does.
I'll be questioning my electronics Whiz contact but the answer will likely be 'it depends' and what it depends on, he would likely need to see the components and would prefer to have a schematic, is my guess.
 
Would love to see the AFD feature of the Blue Sea switch adapted for that purpose, see your PM.
 
OK, PMs disabled.

If you want to ask your guy, I'd be willing to buy a switch, drop shipped out to him, in exchange for a clear step by step, maybe posted by you if you want, your detailed HowTos are amazing!

And I get the switch back when he's done , cover all costs of course.

The things we do for Science! :cool:
 
Air conditioner and refrigerator compressors should turned off and immediately back on. Five minutes used to be the recommended time to let the pressure balance. Some industrial ones had timers to prevent this, but I think most home ones just let the self-resetting over-temp switch trip if the compressor stalled.

Mechanical switches don't care which way the current flows.
 
blars said:
Air conditioner and refrigerator compressors should turned off and immediately back on. Five minutes used to be the recommended time to let the pressure balance.
I'm assuming you meant "should NOT" in the first sentence?

OK, change "counting" to "five minutes" in the above. Maybe an appropriately sized timer relay circuit? Complex, I know.


blars said:
Mechanical switches don't care which way the current flows.
Yes, but what issue does that bring up in this setup? I see everything here as inherently one way.
 
John61CT said:
I'm assuming you meant "should NOT" in the first sentence?
Oops, yes. Just don't flip the switch when the compressor is running, the thermal inertia will provide the delay.

John61CT said:
Yes, but what issue does that bring up in this setup? I see everything here as inherently one way.
This was an answer to one of the replies further up the thread that thought SPDT was only for selecting two outputs, rather than two inputs. It does either.
 
John61CT said:
OK, PMs disabled.

If you want to ask your guy, I'd be willing to buy a switch, drop shipped out to him, in exchange for a clear step by step, maybe posted by you if you want, your detailed HowTos are amazing!

And I get the switch back when he's done , cover all costs of course.

The things we do for Science! :cool:

I was going to ask my guy how switching between 12 and 24vDC on the fly would/could/cumulatively might damage the '350$ to replace' Danfoss compressor controller.  His answer will likely be a large 'it depends' and he would likely need to see a schematic and parts list for a definitive answer, but he would then give then give a 'generally, they would do it like 'this. which is good or bad in this scenario depending on whether they did x b b or possible y and c in addition to x y and Z in reverse order while hopping on one leg with the moon in a 1/3 waxing gibbous phase '

Don't hold your breathe on an answer
 
Maybe cause my ignorance, but tgat is not what I mean.

I am NOT talking about

SternWake said:
switching between 12 and 24vDC on the fly

while ANYTHING is on.

I'm talking about asking him how to use that specific switch, which AFD feature is designed to automatically power down the field current on a high-amp alternator BEFORE the OFF position is engaged, to do the same with the compressor.

So the compressor is automatically shut down when you use the switch to power down the fridge.

Then apparently we need to sit at OFF for five minutes before enabling 'the other' circuit.

What I'm after should be exactly the same functionality as if you had two ON-OFF switches, one connecting/disconnecting each bank to the fridge+compressor (maybe DPDT?), but preventing the possibility of having both circuits ON at the same time (boom!)
 
John61CT said:
I'm talking about asking him how to use that specific switch, which AFD feature is designed to automatically power down the field current on a high-amp alternator BEFORE the OFF position is engaged, to do the same with the compressor.

So the compressor is automatically shut down when you use the switch to power down the fridge.

I guess I'm missing something here.  The AFD kills the power to the alternator fields (the windings that serve as electro magnets) BEFORE the main part of the switch leaves the alternator output with nowhere to go. In other words, the switch is controlling two separate power circuits, input and output.

With a refrigerator, there is only incoming power to the compressor.  I'm not sure what rpm the Danfoss is spinning at, but I would think inertia would leave the compressor spinning  at full rpm even if you killed the power to the compressor for a second via the AFD before hitting it with twice (or half) as much voltage a second later.
 
While this thread title is about the switch, for switching power source from fridge from 12v to 24vDC, I have no personal interest in the switch itself, and I have already typed what my personal solution to this function would be if it were an option in my own system, or I was setting it up for someone else..

My concerns with doing such a thing, would be the possible destroying the Danfoss compressor controller which costs some 350$ to replace, which is likely more than half the price of the fridge itself.

The safest way to ensure that there is no risk, at all, is to make sure that when switching from 12 to 24vdc or visa versa, is that the fridge thermostat is turned off and compressor shuts down. Then after possibly a period of time whose duration is unknown, move the power feed to the compressor controller to from 12 to 24 or 24 to 12v, then turning the fridge thermostat back on.

I have absolutely no interest in a switch, or anything automatic to accomplish this task, as I see nothing but a possible blue smoke release from multiple areas on setting up something which can be accomplished so easily, and safely, manually in 30 seconds? instead of 2.

Now as far as if a quick switching from 12 to 24vdc or back, and how the compressor controller would handle that, I have no idea. It is not a risk I would be willing to assume does not exist, nor that this 'convenience' is worthy of effort or expense. I fully understand other's opinions on the deisre for this convenience, are different.

I do have an interest, though well over my head, regarding the electrical components inside the compressor controller, and how they they would handle, or not handle, and abrupt change in DC input voltage. I will ask my knowledgable source on this possible risk, but that will only take a few moments of his time to type a response. If he chooses to do so. He has chosen not to, or forgotten to respond to some of my questions before, I am not going to ask that he dissect parts and take time from his life and his personal projects where he desires to spend his limited free time.
 
Optimistic Paranoid said:
I guess I'm missing something here.  The AFD kills the power to the alternator fields (the windings that serve as electro magnets) BEFORE the main part of the switch leaves the alternator output with nowhere to go. In other words, the switch is controlling two separate power circuits, input and output.

With a refrigerator, there is only incoming power to the compressor.  I'm not sure what rpm the Danfoss is spinning at, but I would think inertia would leave the compressor spinning  at full rpm even if you killed the power to the compressor for a second via the AFD before hitting it with twice (or half) as much voltage a second later.
No, the ?five minutes? pause on the switch's OFF position is an integral and obviously key part of the process.

It seems to me, as long as that is followed, there will be no problem.

Even more so if indeed there isn't as much complexity, number of circuits involved as I inferred from concerns expressed.

But feels like a dead horse by now, even as a theoretical curiosity issue, I let it rest in peace.
 
A preliminary response from my electronics tech contact says the break before make Switch is vital, as stated earlier in this thread,Here is a cut and paste
My take on a recovery time is that since the fridge power supply is under load by the compressor, and by its own internal losses, and switching power supplies generally don't have the large filter capacitors which were used as substantial energy reserves as in times past, that the collapse of power upon disconnection would be on the order of tens of milliseconds. Most heavy duty switches don't actually move all that quickly, so there would likely be ample time to avoid bridging the input voltages by using a heavy switch.

I would tend towards a rotary switch for this application. They require more time to actuated, and can be had in hefty current ratings.

I went further into my DAnfoss PDF bookmarksd and found this statement:
BD35/50/80F/250GH/100CN: 12V DC systems: 10.4V cut-out (or 9.6V with optional setting) - 17V max. ;
24V DC systems: 22.8V cut-out (or 21.3V with optional setting) - 31.5V max.
The low voltage limits can be established if a connection is made between the terminals C and P, please
see also the passage Optional battery protection settings page 9.
The electronic unit will calibrate to the applied voltage. This means that if the battery voltage is less than
17V, the electronic unit assumes that it is working in a 12V system. If the voltage is higher than 17V, the
electronic unit assumes that it is working in a 24V system. Consequently, the compressor does not run
at power supply voltages between about 17V and the desired battery protection cut-out voltage for
24V systems. A continuous voltage range from 9.6V to 31.5V can be established if a 220kΩ resistor (wiring
diagram item 9) is connected between the terminals C and P. This wide voltage range makes the BD
compressors very suitable for photovoltaic powering.
BD35F/BD35K: Solar systems (electronic unit 101N0400): 10V - 45V, no battery protection
BD35/50F: AC power supply systems: Nominal voltages from 100 to 240V AC,
50/60Hz. 85V min. - 265V max., 50/60Hz. Power consumption is limited
to 100W with the BD50F compressors. Earth connection required.
All voltages are measured on the terminals of the electronic units.

Source:

http://files.danfoss.com/TechnicalInfo/Dila/06/bd_compressors_11-2009_pk100c902.pdf

Page 6.

Please note I still am not advocating this approach, even though my fears of a potential risk to $$$.$$ compressor controller appear to be low/ unfounded.
 
To me the robust Blue Seas is worth the extra $$ for this application, but great to see a cheap alternative for lighter use cases.

In both, the OFF being located between the two circuits guarantees a good Break before Make even if a switch didn't specify.

Thanks so much as usual SW; caution is always a good thing with electricity and pricey gear.
 
Test result here. Indel-B. Compressor not running, pulled fuse, waited a minute or so, plugged in fuse, Inde-B back to on, compressor not running. Compressor running, pulled fuse, waited, replaced fuse, delay in controller, then compressor runs. The digital controller seems to have a built-in time delay when current is disrupted while the compressor is running.
 
Break before make switches are the most common, make before brake are a specialty item you would have to pay extra for. If not specified, it's break before make like 99.9% of switches.
 
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