Auto switch voltage between AC & DC

[Scubadoo]

Does anyone know where I can obtain a dual input (AC & DC Voltage) power supply to Output 12v or 5v DC?

Basically looking for an auto switch power supply that detects which voltage is available either AC or DC. Similar to what is used on fridges that auto detect power input ac/dc.

Thanks.

 

[William_H]

Most people find it satisfactory to run a battery charger into ships batteries when mains power is available. The device you want to run then runs on 12v dc from batteries. So not a changeover as such but really running on 240vAC when available. Even if you want it entirely isolated from ship's batteries you still need a battery of some sort for 12v source. So suggest small charger to that battery.
Now if you really want a changeover device. You need a power supply ( known as a "transformer" ) to give you the 12v or 5v on 240 v AC. This is fed to a small relay which will operate when 240vAC is supplied. The contacts of the relay would be a changeover contact with the output form the power supply at the normally open contact (NO) the 12v source on the normally made contact and the contact that goes between the 2 going to your load. ol'will

 

[Scubadoo]

Thanks William for your comments. I had already thought of several options like leaving the battery charger on etc, however, I was looking for a solution for when the boat is unattended as I don't like to leave the charger on constantly and all the 12v circuits are isolated via the battery switch except the bilge pump.

The idea was to leave the 240v AC on when the boat is unattended, and when onboard to switch over to 12v DC via the battery switch and when away from shore power. I was hoping maybe someone was aware of a changeover device that I could simply plug in rather than build something with a relay as you describe.

My other option is to use a solar panel to top up the battery and simply connect this way without worrying about AC power etc. The current draw I think will be 100ma, so not a huge amount.

 

[Yngmar]

I've just removed such a device from our boat fridge. It is made by Waeco and outputs 24V (as the fridge itself accepts 12 or 24V - but I added a 12V only digital thermostat, so it can no longer cope with 24V). Happy to sell it for a fair price if it helps, although with shipping from Italy I'm afraid. Perhaps Waeco still make them, and maybe even in 12V. It's probably a bit too specialized to find for cheap on Ali/eBay.

They were fitted exactly for the reasons you describe above, leaving AC shorepower connected to keep the fridge running when away from the boat without any risk of draining the batteries.

Update: Found a online seller for the one I've got (alas, only 24V version available, but if your fridge has a Danfoss controller like most of them, it'll be fine): https://cooltechleisure.co.uk/shop/shopdometic-waeco-coolpower-eps-100-mains-adaptor/

 

[matthewriches]

Depending on what you are doing with it then a fridge power pack would be my possible answer too. Although would be good to know your intended application.

Yngmar - if you'd like to sell your fridge power supply and the OP is not interested, could I be considered? My saloon fridge supply has blown the mains board and I cannot repair as chunks have blown off it!!

 

[Scubadoo]

Thanks yngmar, unfortunately it is not quite what I am looking for, I think yours is simply converting AC to DC, whereas I am looking for two inputs AC & DC to DC, ie switching on sensing between AC & DC.

The purpose is not for a fridge but a couple of 5v USB devices suchas mifi router and other equipment which will be hard to access to manually swap over connections, so was thinking of a device to do this for me and save draining the battery when not on the boat to remote access etc.

 

[rogerthebodger]

Thanks yngmar, unfortunately it is not quite what I am looking for, I think yours is simply converting AC to DC, whereas I am looking for two inputs AC & DC to DC, ie switching on sensing between AC & DC.

The purpose is not for a fridge but a couple of 5v USB devices suchas mifi router and other equipment which will be hard to access to manually swap over connections, so was thinking of a device to do this for me and save draining the battery when not on the boat to remote access etc.

Am I correct in saying your USB devices of power by 12 VDC either through a mains to 12 VDC power pack or direct from the boats 12 VDC supply.

If so all you need id a mains relay connected to the incoming mains supply that will switch the 12 VDC output from the power pack to the USB device. When there there is no mains supply the relay will de energise and connect the boat 12VDC supply to the USB device.

A simple double pole changeover relay with a 240VAC coil will do the job.

 

[Yngmar]

Thanks yngmar, unfortunately it is not quite what I am looking for, I think yours is simply converting AC to DC, whereas I am looking for two inputs AC & DC to DC, ie switching on sensing between AC & DC.

Nope, it has DC input terminals as well as output. If AC input is present, the DC output is supplied from the AC (converted to 24V DC) and if there is no AC it switches the DC input through.