Recommended kit: laptop USB charging

[wakey_wake]

In the car I used to charge my laptops with laptop-specific boost power supplies like these,

https://www.amazon.co.uk/TAIFU-Universal-12V-24V-Pavilion-Thinkpad/dp/B07W5DD6M9/

(not a recommendation). The one I had has a switch for output voltage (16~22V ish) and has several times had a different plug soldered on the end as laptops come and go.

 

My current laptop will take a 19V barrel connector or standard USB C power delivery. This is really neat and more kit will be going the USB C way.

 

After using an Apple USB PD charger for a while, I realised that this combination is really useful -

• 12v to 24v boost converter e.g. https://www.amazon.co.uk/s?k=24v+boost+converter . The ones sealed into a heatsink case are especially nice, but anything that gives 21~30V will do.
• a USB PD3 / QC4 board e.g. https://www.amazon.co.uk/gp/product/B09658Z4FF/

 

Assuming you're happy to wire up stuff like this. The board will need some physical protection - mine are currently just in heatshrink, and they do put out a little heat while running so you can't box them in completely.

 

You can run the PD3 board off 12V, and you can charge a phone at 5V with the standard USB A or USB C connectors whatever supply voltage the board has (in its range). It will auto-negotiate, that is what the USB Power Delivery and Quick Charge standards do.

However these boards can only "buck" down, it won't "boost" up. Therefore a laptop which wants 20V to charge needs the PD3 board to be fed by a 24V-ish supply. This was my important realisation for laptop-in-car usage, which means my old laptop PSU is obsolete.

 

Other things to consider,

• The 24V boost converter I have uses about 12mA when idle. There will also be conversion inefficiencies, probably about 85% but I haven't checked.
• The PD3 board also has an idle current, if you don't switch it off when not using it. You can unsolder the LEDs to save some idle power but that doesn't make a huge difference.
• There is some protection from having the input to the 12-to-24 boost converter fused, and it has a limited current output, but you still want a suitable fuse and fat-ish wire for the PD3. Laptops are going to draw several amps of 24V, so check the maximum power given by the factory charger.

 

Lots of other USB charged kit I have only needs 5V. The supplies for these are often marked "5V 2.4A" or similar, and as long as the cable & fuse are good they're perfectly suitable for charging phones and stuff off the boat. Modern / hungry phones though will benefit from QC or PD supplies, and the Android tablets I have won't charge off 5V non-QC.

 

 

In my case I've also switched the fridge over to 24V supply, because it can take it. There is no point doing 12-to-24 at the bow so I just have one run down the boat at 24V, but the cost/benefit of this doesn't add up by itself.

• The fridge already had a fat 8AWG cable, so 12V losses are not huge
• The idle current of the 24V supply is always-on, while the fridge is mostly off, so that's wasted
• The boost inefficiency means the largest low voltage power user might actually be using more

 

If it was important I would take some measurements...