A useful voltage regulator.

Keywords. 12v DC voltage step-up regulator. Buck transformer. Under-voltage.

This neat little unit can sort out several problems or upgrades in the van - not just a Hymer, but any vehicle with 12v DC electrics.

What it does is take a variable voltage in, and delivers a steady output at a voltage set by the user. The input voltage can vary but the output voltage will remain constant.

There are two main uses in a classic motorhome.

The first is to fix any problem that is caused by equipment cutting out as the battery voltage falls. This can apply to old Truma heaters like the 2800. Although it runs on gas, it needs 12v to run the fans and safety circuits. As the voltage falls, they are designed to cut out at around 11.5v. However this can vary as the equipment gently ages - I ended up with a Truma 2800 that was randomly cutting out at above 12v so I installed one of these and it neatly solved the problem. I set it to a deliver a constant 13.8v.

The second common use is to power equipment that is DC powered, but needs more than 12v. In my case this was a really nice Samsung Smart TV. In the showroom I noticed that rather than the usual 220v AC power cable, it had a power brick and a DC plug. Closer inspection revealed that the TV ran on 19v DC. Using one of these modules I am running the TV directly from the leisure battery. There is a small conversion loss, but not really noticeable. There is a lot of equipment on the market that runs on 19v DC - using a unit like this enables you to use it.


There are many similar modules on Ebay, sometimes at a fraction of the price, but these mainly come from China and take weeks to arrive. You also need a meter to set them up properly. I found this one for around £8 from a UK supplier. It has a digital display which displays both the input and output voltage, so is really easy to set up. This unit also has quite a high power rating, up to about 10 amps or so, but I run at about a quarter of that so it runs cool to the touch.

If you are thinking of running/charging a 19v laptop (a common voltage for many laptops) then you must pay close attention to the power requirement. Most laptops are around 60 to 90w, and this unit is rated at around 65w, so is on the borderline. It would be OK for mini laptops - chrome books etc, but probably not man enough for a big laptop. Look on the power brick of the laptop for the power rating. If you need more power, then there are other higher power units available.

You should also note that a unit like this is not a universal cure all for a flat battery! ie you shouldn't expect it to bump up a battery that is going flat and deliver a constant 12v. It will help in situations as I have described, but you get nothing for free. As the battery voltage decreases, the unit will compensate and maintain a constant output, but the current will go up accordingly, and as you draw more current, the battery will flatten even quicker. You must not use a unit like this to camouflage an old battery that needs replacing anyway. But it works very well in similar situations to the two I have described.

The Ebay description for the one I used is "100W DC 3~35V To 3.5~35V LED Voltmeter Step-up Adjustable Power Boost Module"