Why won't tablet charge directly from 12v supply via fuse block?

Q

QPiepelr65

Ford Transit Connect
Rather than repeat myself here is a post I made already elsewhere and people have come up short as to solutions. Floating here to see if anyone has any other possible solutions.

I reaaaally don't want to have to do the whole dc to ac back to dc as it seems silly and very convoluted. When building my system I had no intention of incorporating ac and still do not want to just for this. If all else fails I would just buy a different pc instead that could charge from battery or rather usb if starting from scratch. It seems a shame to waste a tablet that has been given to me though to want to ensure I looked at every possibility. Even so the dc ac dc still seems pointless to me as in that case due to costs I would still prefer just getting a compatible machine.

Below is an image of the charger with power specs.

Here is an amazon link to the device itself showing its specs.

As you will see from the original thread the issue is the device charge indicator will light up when plugged in to fuse block indicating charge as well as indicator showing on windows however it never charges or at least so slow as to be imperceptible and even leaving on a full overnight it had not increased when I looked in the morning. I tried changing with a new barrel head in case the connection could be at issue but no difference.

Ideally I want to be able to charge it direct from the fuse block but am stuck and don't understand why it doesn't pull the right amount of juice to charge.

smaller.jpg
 
My guess is there's OVP (over voltage protection) built into the charge circuit on the tablet. Not usually something on lower end devices, it's more common on high end or at least what I'm experienced with and that's medical devices. If it charges OK on the ac adapter then a simple dc dc buck converter to keep it at 12v rather than 12.8-15v of a vehicle battery should suffice.
 
Do you know what voltage is being supplied at the fuse block when the device is connected ?

The link isn't working for me.

Some devices charge intelligently and it may be that the voltage being supplied isn't quite right.

Pete
 
plug the adapter in and use a volt meter to get the real voltage from the power adapter.

the case shows 12vdc @ 3A. - but it may be higher?

................

assuming the engine isnt running, you should get 11.9v - 13.6v from the van.

if the van is running you may get 11.9v - 15v,

+++++

a lot of electricals can be fussy of voltage. . . so you might need to use a mini dc-dc regulator and set it to 12v output.

............


the other option is that you are getting volt drop on your charge cable. so its trying to pull 3A, but is getting a drop off in voltage, causeing the tablet charge to role back.

....








1709015785323.png
 
Reading the description in the picture, first bullet: "the input should be 3V higher than the output"
It is a step-down converter only, not buck-boost
 
Pete C said:
Do you know what voltage is being supplied at the fuse block when the device is connected ?

The link isn't working for me.

Some devices charge intelligently and it may be that the voltage being supplied isn't quite right.

Pete
Click to expand...
i havent checked while connected but have checked the barrel for power and polarioty before and was ok. i dont have a recent voltmeter to give fine grained readings. it is my late grandads probably from the 50s or so which only has a needle so only roughly showing the volts. i know new ones are cheap but had not had cause to upgrade until now.
 
Dellmassive said:
plug the adapter in and use a volt meter to get the real voltage from the power adapter.

the case shows 12vdc @ 3A. - but it may be higher?

................

assuming the engine isnt running, you should get 11.9v - 13.6v from the van.

if the van is running you may get 11.9v - 15v,

+++++

a lot of electricals can be fussy of voltage. . . so you might need to use a mini dc-dc regulator and set it to 12v output.

............


the other option is that you are getting volt drop on your charge cable. so its trying to pull 3A, but is getting a drop off in voltage, causeing the tablet charge to role back.

....








View attachment 230978
Click to expand...
as reply above. i am using leisure battery btw not starter so i guess talk of engine running doesnt apply?
 
How can a 3 pin plug attach to the fuse block? You can't use that adaptor without using an inverter. If you cut off the wire and connect the wires to the fuse block then you are bypassing the plugs internal voltage controls and risk damaging your tablet as the car/leisure battery supply voltage fluctuates. (the leisure battery has a dc-dc charger I assume?)
If that plug works at home then I would buy a cheap low wattage (150w) inverter for £20 off amazon and hard wire that to the fuse block instead. I know you said you can't see the point of dc-ac-dc but if it works and gets the job done then it's the easiest solution and you can then move on with your life.
 
ShooglyStu said:
Reading the description in the picture, first bullet: "the input should be 3V higher than the output"
It is a step-down converter only, not buck-boost
Click to expand...
which image are u referring to mine of the adaptor or later amazon link by other poster?
 
Howzat said:
How can a 3 pin plug attach to the fuse block? You can't use that adaptor without using an inverter. If you cut off the wire and connect the wires to the fuse block then you are bypassing the plugs internal voltage controls and risk damaging your tablet as the car/leisure battery supply voltage fluctuates. (the leisure battery has a dc-dc charger I assume?)
If that plug works at home then I would buy a cheap low wattage (150w) inverter for £20 off amazon and hard wire that to the fuse block instead. I know you said you can't see the point of dc-ac-dc but if it works and gets the job done then it's the easiest solution and you can move on with your life.
Click to expand...
i never said i was using that in the van. yes the plug works as intended at home charging in a couple of hours. the whole point is i dont want to use an inverter. i posted that image only as reference to show the original adaptors power requirements when used in the house, which is aside from using in the van. in the van i have made a fused wire with the correct barrel connector to plug into the device which is connected to fuse block which in turn is connected to leisure batt.

hmm i wasnt aware they would only be 20 quid. i assumed more like 60-80. even so, if at all possible i would like to connect direct to fuse block, even if more work, if it can be done. call me a stubborn bugger but just like the idea but if all stones are overturned and still nothing comes up i may then admit defeat but want to make sure i tried all other options first.
 
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i suppose the main issue is trying to diagnose the issue in order to know how to proced. so i shuld find out the voltage being supplied while plugged n to help with that, will that help illucidate a solution if there is one?

having checked with the imperfect voltmeter i have currently just at the barrel when unplugged at pos and neg it certainly looks close to 12 though could be a margin between 10-14 odd. would that be different when trying while plugged in, which i havent tried yet?
 
QPiepelr65 said:
which image are u referring to mine of the adaptor or later amazon link by other poster?
Click to expand...
Referring to amazon image posted by @Dellmassive as the link in your OP is broken

You probably want something like this:
 
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I suspect your leisure may only just be at 12v or maybe even a bit below and with load it drops v's hence the issue you're seeing.
Does the device charge % go up any quicker if the leisure is charging via hook up or DC whatever your setup is?
 
Howzat said:
I suspect your leisure may only just be at 12v or maybe even a bit below and with load it drops v's hence the issue you're seeing.
Does the device charge % go up any quicker if the leisure is charging via hook up or DC whatever your setup is?
Click to expand...
Ah I can actually tell you the battery voltages because I look at them constantly every day on my mt50 readout for the solar charge controller as a rough guide to see state of charge. The voltage is never at 12, as from what I understand from lifepo4 charging levels that would mean 0% charge. Currently it is fluctuating around the 13.3 to 13.5 range.

So it will always be above rather than below if we are talking the battery voltage itself.
 
QPiepelr65 said:
Ah I can actually tell you the battery voltages because I look at them constantly every day on my mt50 readout for the solar charge controller as a rough guide to see state of charge. The voltage is never at 12, as from what I understand from lifepo4 charging levels that would mean 0% charge. Currently it is fluctuating around the 13.3 to 13.5 range.

So it will always be above rather than below if we are talking the battery voltage itself.
Click to expand...
Well that leaves over voltage detection on the device as the no1 culprit.
So looks like the solution is a step down as @Dellmassive suggested or an inverter or a new device.
 
Howzat said:
Well that leaves over voltage detection on the device as the no1 culprit.
So looks like the solution is a step down as @Dellmassive suggested or an inverter or a new device.
Click to expand...
Ok. Upon these suggestions I had a look again at the amazon advert and the voltage states it runs at only 3.7 volts. Would that mean it wants a charge at around the same voltage as that? If so then clearly it is far away from 12v of the battery.

Upon your recommendations I bought this device (awaiting arrival) which seems to be able to adjust voltages on both sides meaning I could test different ones until hopefully something worked. For the input voltage what should I set it at though since my battery is not at a constant but rather ranging from 12s up to 14.4? EDIT: Ah it looks like only the output voltage is adjustable which makes things simpler. Will anything around there suffice? Also the device is rated at 5a which is more than the 3a the wall charger is rated at. Will this be a problem?
 
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QPiepelr65 said:
Ok. Upon these suggestions I had a look again at the amazon advert and the voltage states it runs at only 3.7 volts. Would that mean it wants a charge at around the same voltage as that? If so then clearly it is far away from 12v of the battery.

Upon your recommendations I bought this device (awaiting arrival) which seems to be able to adjust voltages on both sides meaning I could test different ones until hopefully something worked. For the input voltage what should I set it at though since my battery is not at a constant but rather ranging from 12s up to 14.4? EDIT: Ah it looks like only the output voltage is adjustable which makes things simpler. Will anything around there suffice? Also the device is rated at 5a which is more than the 3a the wall charger is rated at. Will this be a problem?
Click to expand...
This item is step down only. In other words, for a 12v output you will need an input of at least 15v. With an input of 12.5v from your battery, the output will likely be 10v at most.

You need a buck-boost converter like the one I linked above. Note that some adverts can be misleading, they may say "buck" and "boost" but the converter may not support buck-boost, you need to read the details.

Input voltage: 9 ~ 20V DC
Output voltage: 12V±0.2V DC
 
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