DC-DC supply for router.

Glas Robin

Glas Robin

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I have a spare EE home broadband router which I’ve repurposed as a router in the motorbaguette to keep everyone happy. Our home SIM comes with us when we are travelling. Outside of the van we just use our phones, so no point buying a mifi unit.

It’s great when we are on EHU as we just plug in the usual 240v charger power supply which outputs the 12v 2a that the router needs. Less useful when we are off grid. I’m succumbing to the plaintive wailing of the kids who can’t live without a stable connection. We much prefer to be off grid than on organised sites.

I was thinking of hooking one of these into a 12v lighting circuit, and chopping the socket off the end of the adapter, so we have a simple 12v dc-dc supply for the router regardless of whether we are on or off grid.



Anyone see any problems?

Thanks.
 
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To be honest for the cost of the above kit you could get a good MIFI which you can run direct from 12v.
 
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this will work as its stabilised at 12v. running straight off the leisure battery could see 14 volts at times and those routers are sensitive
 
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TheBig1 said:
this will work as its stabilised at 12v. running straight off the leisure battery could see 14 volts at times and those routers are sensitive
Click to expand...

Thanks. Isn’t that exactly the same thing electronically (except yours has a fixed current output) but in a nicer case and with a cigarette socket adaptor?

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Making a stable 12 volt supply from an automotive supply is more problematic than stepping down to 5 volts for a USB supply, or stepping up to 19 volts for a laptop supply. The automotive supply can vary from below 11 volts to above 14.5 volts. For full regulation, a supply must be able to step either up or down as required, and is known as a 'buck/boost' supply.

Some supplies, including the one in your link, will only step down and will not step up. It needs some 'headroom' above the output voltage, so will probably not give 12 volts out if the input is less than 12.5 volts. It's not a problem while the engine is running, but after a long stay without EHU the battery voltage could easily be 12.5 volts or less, and the output voltage will drop too.

Routers designed for a 12 volt mains-powered supply will probably be very fussy about the voltage, and will probably be damaged by the unregulated automotive supply. A step-down supply like the one in your link will probably have problems as the battery discharges and the supply input drops below about 12.5 volts.

The supply in @TheBig1's link is described as 'fully regulated', so should be both step up and step down if that is true. I'm not 100% convinced by the description, but I may be wrong - I'd only be sure if I tried it out for myself. Maybe someone who's used one can verify it's OK.
 
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I have run several "12vdc" routers and mifi that have come with 230vac power supplies. I connect them direct to the 12vdc house circuit in the van as you are proposing with to date no issues. The voltage will mostly be 13-14vdc or so. There are 12vdc cigarette plug adapters and these do not have voltage regulators incorporated. Many years ago when I was fitting similar kit to my boat I sought out routers and switches (ethernet) that ran from the former power supplies specifically so I could hard wire them into the boats house bank. They all worked for years. I have had 3 routers in my Rv and motor homes, together with a Ubiquiti bullet in each with no ill effects. As your unit is used anyway what have you got to lose? You just need a cable with a jack to match the router check its dimensions and polarity.
 
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I would not hesitate to connect it directly to the 12v sockets. Never had an issue with any piece of equipment that normally used a 230vac/12vdc adapter and that includes TVs, Media Players etc.
 
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12V to 12V is really 10.6-14.7V to 12V, so you'll need this device:



If you can persaude it to run at 9V you can buy the 10A buck (down) converter as it's more efficient, but if you need 12V you need the above device.

You need to adjust it to the correct output voltage with a multimeter before using the output. Also don't leave it permanently connected as it will always draw a small current. I have one for my LED dome lamp and it works quite well.

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Thanks all. Will go with a buck boost and report back when I've fitted it.

Incidentally - since the router supply is 12v 2a - does that mean it is drawing 2amps per hour whenever on? ie with a 95ah AGM leisure battery it will drain the battery to around half in 24hours?

Or is the actual current drawn different to what the supply is rated at?

Schoolboy electronics is a good 30 years ago for me....
 
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Glas Robin said:
since the router supply is 12v 2a - does that mean it is drawing 2amps per hour whenever on? ie with a 95ah AGM leisure battery it will drain the battery to around half in 24hours?
Click to expand...

It just means the router wants a 2A supply, it may use that at startup or all the time or under heavy (network) traffic, difficult to say.

Assuming for safety it wants 12V 2A all the time that's 24W. Add in a double converter like the one I linked to and that's probably worst case 85% efficient so you need to supply it 24 / 0.85 = 28W.

Switch-mode devices convert powers to powers so to supply 24W at an efficiency of 85% it will suck 28W out of your leisure battery. That's about 2.25V if your battery averages 12.5V - so it's similar in this case because the voltage you are converting to is very similar than the one you are converting from.

If it really does use 24W it should get slightly warm, you can always meaure the current it draws in normal usage with a meter like this:
https://www.ebay.co.uk/itm/UNI-T-UT...-AC-DC-Multimeter-Diode-MAX-Mode/153326790916
 
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BTW if you are using your leisure battery more rather than just buying a bigger one you should consider adding a solar panel, even if it's a portable temporary foldup one, a small 50W one should replace some/all your router uses in most weather.
 
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GPW said:
BTW if you are using your leisure battery more rather than just buying a bigger one you should consider adding a solar panel, even if it's a portable temporary foldup one, a small 50W one should replace some/all your router uses in most weather.
Click to expand...

Thanks. It's on the list - especially as we are planning to be charging electric scooters too (there's another thread about this somewhere), as well as the usual phones, laptops, LED lights, heater fan and water pump.

But first off, I'm planning to assess our off-grid consumption/travel plans before deciding what size battery bank and solar kit to invest in. I reckon it's one of those things you should do once and right first time (or so the ever-fragrant MrsW advises me!)
 
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Sounds like MrsW has approved a proper off-grid mains upgrade to me, involving big Victron Multi inverter chargers, MPPT Solar and neat little rows of AGM batteries :D

Just keep the 'But you told me to do it properly dear' phrase to hand when the card bill comes in LOL.
 
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