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Bypassing power bricks and wall warts.

corporate.joe

Solar Enthusiast
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Jan 25, 2021
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If I were to delete some of these power bricks and wall warts for low power laptops or an LCD monitor, how would I go about determining the allowable voltage range for these devices?

Lets say we have a low power PC and a monitor that both use 19.5 volt AC-DC power bricks, each near 50 watts max. How could I determine the upper voltage range these devices would accept without damage? I would like to find out if these or similar devices could be powered on an 8s LiFePo4 battery that can of course vary between 20-29 volts with out employing a buck converter.

I'd imagine that inspection of the ratings on the capacitors or perhaps some other components nearest the input would be informative but beyond that it could get expensive testing such devices with my variable DC lab power supply to see when things heat up or let out the magic smoke.

Anyone have a rule of thumb to find this kind of information out? Would manufacturers be forthcoming with this information when asked?
 
Anyone have a rule of thumb to find this kind of information out?

Yes. Provide as close to the specified voltage as possible.

Would manufacturers be forthcoming with this information when asked?

Probably, but actually finding someone that knows the answer is the big challenge.

Use a voltage regulator.
 
I saw a video of a Spanish speaking man that connects devices with a transformer like the one a laptop or PC monitor have to 220V DC approx. from solar panels and they work. It even used an electric cooker but he constantly mentions what he is doing is risky and dangerous.

Using 19,5V DC from a battery, even If you regulate the voltage with a buck is in most of the cases a waste of time. Most brands have laptop chargers with 3 cables and the third performs some checks to evaluate whether the charging can start. Fooling that system is difficult. I tried and the charging was not starting.
 
I saw a video of a Spanish speaking man that connects devices with a transformer like the one a laptop or PC monitor have to 220V DC approx. from solar panels and they work. It even used an electric cooker but he constantly mentions what he is doing is risky and dangerous.

Using 19,5V DC from a battery, even If you regulate the voltage with a buck is in most of the cases a waste of time. Most brands have laptop chargers with 3 cables and the third performs some checks to evaluate whether the charging can start. Fooling that system is difficult. I tried and the charging was not starting.
You can not connect things like transformers to DC. I've run some electronic wall warts with as little as 60V DC right from panels. These will have reduced current at this voltage. and get hot Over 120V DC you should get full current. I run lots of things from panels as I also have a 120V array. Your results may vary, some supplies will not work at all if they use voltage doubling. I don't really care if things burn up, your feelings may be different.
 
If I were to delete some of these power bricks and wall warts for low power laptops or an LCD monitor, how would I go about determining the allowable voltage range for these devices?

Lets say we have a low power PC and a monitor that both use 19.5 volt AC-DC power bricks, each near 50 watts max. How could I determine the upper voltage range these devices would accept without damage? I would like to find out if these or similar devices could be powered on an 8s LiFePo4 battery that can of course vary between 20-29 volts with out employing a buck converter.

I'd imagine that inspection of the ratings on the capacitors or perhaps some other components nearest the input would be informative but beyond that it could get expensive testing such devices with my variable DC lab power supply to see when things heat up or let out the magic smoke.

Anyone have a rule of thumb to find this kind of information out? Would manufacturers be forthcoming with this information when asked?


I always treat devices such that they need the exact voltage that the wall wart was providing. I have done this with all my AC equipment to make it run on DC (various input voltages). It also provides a better safety-net to do DC-DC stabilizing. I will post a few useful links.

I have purchased a bunch of DC-DC converters from here, as they have a great selection (scroll down the list to see all the input voltage options), this is probably the best link here. I bought a couple here for stabilizing DC-DC for a bunch of routers I had running off battery power.

I recently bought a bunch of these for Raspberry Pi's and they seem to work good up to 60v DC input:

This one is a boost rather than buck, but it allows me to connect my Makita XRM10 bluetooth radio/battery charger 24v input to the 12v on my truck:

This one, is good for 12v 6a boost to laptops up to 24v (I had purchased 2 back in the day):

I bought 2 of each these before, for mine and wife's MacBooks:
and:

Here's another one I had thought about buying before (also can do boost):

I've also used several of the boost/buck converters like from Drok on Amazon, where you can set the output to CC or CV to get custom setting, like one of these examples (some of their models even have LCD voltage displays):
or:

These style you find on Amazon, don't all do buck AND boost, so if you want both in one converter, then make sure it says boost/buck (or else it may only do one or the other)...

When I'm shopping converters, I always look at the input voltage range, and make sure it falls within my boundaries...

Anyways, you can filter through the above links and decide if any of these seem useful in your scenarios or not...
 
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Some good discussion in here. I'll have to look at these links. I've browsed the following site in the past when I was really interested in building a car PC for mp3 playback and the like. This was some years ago(almost 10) before the head units with bluetooth and SDcard/USB mp3 playback got very affordable. I've managed to find a fairly intelligent DC-DC 100 watt adjustable output voltage power supply. Wide input range. Sounds pretty neat. Can change the settings via USB connection.


They have a 100 watt and 200(150 cont.) watt version. This whole idea started when I switched to using a low-power very small form-factor PC for day to day use. I have it velcroed to the back of my 32" monitor and I noticed that both of them operate on 19.5v bricks. Monitor maxes out at 50 watts and the brick for the HP elitedesk 800 maxes out at 65 watts.


Joe-
 
Most brands have laptop chargers with 3 cables and the third performs some checks to evaluate whether the charging can start. Fooling that system is difficult. I tried and the charging was not starting.

Correct. I made a step-down from 24V to 19 for my Dell Latitude 7440. Power-On-Self-Test beeped and complained it was not an "approved charger". It did charge, but then it would only run with the charger connected - even its own one, even though the battery was full.

It took months to fix. I scrapped the DC-DC adapter.
 
Correct. I made a step-down from 24V to 19 for my Dell Latitude 7440. Power-On-Self-Test beeped and complained it was not an "approved charger". It did charge, but then it would only run with the charger connected - even its own one, even though the battery was full.

It took months to fix. I scrapped the DC-DC adapter.
On Youtube you can find a video of a guy by-passing that Dell charger security check. It's like the third cable needs to sense there is a certain current flow available or so. Your experience is confirming us that doing tests this way is not advisable. What a pitty...

My failed test was with a Lenovo. Fortunately it did not have consequences; but it did not charge at all.
 
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