Adapter for 12 volt DC > 4 volt DC

The common USB adapters (12volt to USB) are five volts out.

When I need a strange voltage...I design and build one.. If you are any good at electronics I can suggest resource material.

while lead acid batteries love to be kept at 100% charged.

Lithium Chemistries do not.

Leaving the battery 100% charged at all times will lead to earlier failure.

USB devices still work and charge fine anywhere from 5.30 to 4.75 volts.

I have a USB power meter that reads volts amps and counts mAH. An enlightening tool.

http://www.amazon.com/Jelly-Comb-Universal-Multi-meter-Voltmeter/dp/B00NHHP06C/ref=sr_1_5?s=hi&ie=UTF8&qid=1428516836&sr=1-5&keywords=usb+power+meter

One gets to see the voltage drop on the cabling used from power supply. I found some usb sources and their cables were insufficient to let my phone charge at full rate. I found other cables would never let it charge at more than half the rate.

I like that 5 amp e bay link to the voltage bucker. I've got a bunch of 2 amp ones I've yet to employ, but one with a voltmeter included keeps a 180MM fan from overheating on full speed at battery charging voltages.

The Jetpack has an internal power supply with its own regulator. The battery is certainly not connected directly to the 5V or whatever input. I would guess that the electronics operate at 3.3V or possibly a lower voltage (for the digital parts, at least). The analog/RF parts might have multiple supply voltages generated internally.

In general, any device with a Li-ion battery is not going to have the external power supply connected directly to the battery, as these batteries require some care and control in charging and discharging to prevent fires and other problems.

As for a supply for the Jetpack, there are many DC voltage converters and regulators available, and a bunch of reasonable suggestions have been made. The old school approach would be to hook up something like a 7804 (fixed 4V) or an LM317 (adjustable) voltage regulator, although these devices aren't particularly efficient as they're linear voltage regulators. You'd need to have an adequate heat sink for them.

There are lots of different models of dc to dc converters on eBay. Do a search on "dc to dc converter step down" and choose one with the right current capacity and price.

I'm wondering about the safe voltage to supply to the Jetpack. I understand that USB voltage is 5 volts DC, but I wonder if the presence of the Jetpack battery in the circuit lowers that voltage some (the battery is marked 3.8 volts DC). So, if I use a USB power supply - at 5 volts nominal - and do not have a the Jetpack's battery installed - would I supply a harmful voltage to the Jetpack?

My desire to run the Jetpack without an installed battery is that my original Jetpack battery swelled up. I have a replacement battery on order, but I noticed that the OEM batteries that I prefer are not in ready supply (not even from Verizon). So since I usually have the Jetpack connected to the RV DC system, I really don't need a Jetpack with a battery if I can connect it directly to the RV system; and thus eliminate any issue of over-charging the lithium battery.

I recommend going online to Amazon or battery plus
And buying a replacement battery,
And not leaving it on charge 24/7
My phone is my hotspot, and spend too much time plugged into a 12v to 5v USB charger
I replaced the battery, and try not to leave it on charge when not being hotspot

You might be looking for one of those 12VDC sockets with the USB charge ports on them... These are available at alot of places like WALMART AMAZON etc...



I use one these all the time to keep my VERIZON MIFI Unit charged from my 12VDC sources. Of course my battery is still good inside the MIFI unit however...

There are also some multi-voltage TAPs devices from radio Shack or AMAZON...


these plug into a 12VDC socket and you move a selectable DC VOLTAGE TAP to the DC voltage you want to have available...

If it was me I would just get another JETPACK battery... I use my VERIZON MIFI in my shirt pocket for alot of outings when camping - neat sitting at the beach and having all of our tablets and devices working from the MIFI generated WIFI HOTSPOT...

Roy Ken

Verizon or Amazon Amazon