12V Switching Ideas

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I have a 12V portable fridge/freezer mounted in my tow vehicle. It can
be run from either the car battery when the engine is running or from
an auxiliary 120AH deep cycle battery when parked. The deep cycle
battery is solar charged from a 130W panel mounted on the roof of the
tow vehicle. I've set it up this way because we often camp for days
away from power so we can't depend on a traditional "dual battery
management" system to keep the auxiliary battery topped up while
driving.
At present I'm using a simple SPDT relay to automatically affect the
switching, driven by whether the ignition is on or off. All well and
good except - when the ignition is turned on the relay is energised
and switchover is 'instant'. However, when the ignition is switched
off, there is a momentary pause before the relay de-energises and
trips to the auxiliary battery. This causes the fridge compressor to
stop and then a second later, restart. Most unhealthy for fridge
compressors. I need a simple seamless switch from one source to the
other. Can I 'buffer' the existing switchover? Or is there a better
way to achieve what I need? Can anyone help?

Cheers
Mark

Re: 12V Switching Ideas

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What I have done is to make a circuit up that provides a ground for the
switching relay once the oil pressure light has gone out, so that power is
held off until the engine is running. This will also stop the deep cycle
being connected to the main battery.
This same circuit is also used for the grounds of relays for other stuff
(air comp etc.) that need the engine running for use.

Cheers ............ Rheilly P



Re: 12V Switching Ideas
Thanks Rheilly. I was thinking about a blocking diode to protect
against my deep cycle battery ever being called on to provide starting
current. Thanks for your suggestion, but I'm trying to make the
switchover faster not slower by having to wait for the oil pressure
light to go out.

Mark


Re: 12V Switching Ideas
the way you have the system wired is wrong
what brand and model solar reg you using?



Re: 12V Switching Ideas
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Paul it is a Morningstar Sunsaver 10. It is wired according to the
manual that came with it, at least I reckon that it is.
A forum member, Mike, has been good enough to work with me in setting
up a simple "Diode Auction" circuit using a pair of Schottky diodes.
Basically running the fridge permanently from the auxiliary battery
and switching the charging source, whichever is available and putting
out the higher voltage. I've finished the construction and will test
this afternoon or tomorrow.
Thank you for your suggestions.
Mark

Re: 12V Switching Ideas
Not the best idea. VSR is better option.

news:ef79b600-6ca9-4b45-aca8-

Paul it is a Morningstar Sunsaver 10. It is wired according to the
manual that came with it, at least I reckon that it is.
A forum member, Mike, has been good enough to work with me in setting
up a simple "Diode Auction" circuit using a pair of Schottky diodes.
Basically running the fridge permanently from the auxiliary battery
and switching the charging source, whichever is available and putting
out the higher voltage. I've finished the construction and will test
this afternoon or tomorrow.
Thank you for your suggestions.
Mark



Re: 12V Switching Ideas
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I suspect you have a wire to the the normally open relay contact
from the ignition (or accessory) circuit.  run that vire instead
from engine battery (via a suitable fuse)  or from the wire that
supplies the horn and dome light circuits...

the turn off delay is not long enough to drain your battery.


















Re: 12V Switching Ideas

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I would be lazy and just put a diode from the battery side of the relay
switch to the compressor side.
When the switch is set to battery the diode is shorted and does nothing.
When the switch is on the car side the diode will be slightly reversed and
won't conduct (because you will tie the returns)
When the switch is switching the diode will provide enough power for the
compressor.





Re: 12V Switching Ideas
On Fri, 30 Jan 2009 19:29:08 -0800 (PST), 2EZY

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Run it from the aux battery all the time, then have a voltage
sensative relay (VSR) charging it from the vehicle. This is the
standard way of doing it, and it ensures that your starting battery
always gets charged first.

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