Getting 12 volt from 48 volt supply?

[JohnW2]

Seeing @chivers67 post, and the CO2 inflater, that seems a better option.

It might well be, if not some sort of hand pump.

You still have not given me any indication of what sort of current your pump draws at 12V.

Kind Regards, John

 

[davelx]

Why not an ordinary hand cycle pump?

A 12v 3amp series regulator is cheap and the fact they waste current would not be much of an issue for short use, but the last I was involved with were only speced to 30v. No doubt the 30v limit will have improved since then, or run two in series.

However you do it, with linear regulators to get from 48V to 12V at 10 amps (eg) you have to dissipate (waste) 360W. That's a very big fan cooled heatsink. It really has to be a DC-DC switcher, I think

 

[JohnW2]

However you do it, with linear regulators to get from 48V to 12V at 10 amps (eg) you have to dissipate (waste) 360W. That's a very big fan cooled heatsink. It really has to be a DC-DC switcher, I think

All true. However, I would suspect that erics "e-bike tyre pump" might well use far less than 10A (at 12V), which is why I've repeatedly asked him about it's current draw. If it's fairly low, then dropping the voltage with, say, an appropriate incandescent bulb in series might possibly be a realistic option. The actual 'wastage of energy' would not really be an issue for such occasional and brief use.

Kind Regards, John

 

[Jackrae]

I cannot help but think this really is a silly request. Yes, the question is good but why drag a none-too-light air compressor plus invertor around for the possibility that you MIGHT want to reinflate a leaky tube just because you have an electric bike. It doesn't quite gel in my mind. I surmise a small hand pump or a CO2 inflator makes much more sense, both being lighter and neater.

The percieved electric solution is not unlike someone, who has just bought an all-electric car, wanting to fit a pertol generator into the boot so's they can recharge the battery in the eventuality that they MIGHT run out of battery capacity. Hybrid cars excluded !

 

[JohnW2]

I cannot help but think this really is a silly request. Yes, the question is good but why drag a none-too-light air compressor plus invertor around for the possibility that you MIGHT want to reinflate a leaky tube just because you have an electric bike. It doesn't quite gel in my mind. I surmise a small hand pump or a CO2 inflator makes much more sense, both being lighter and neater.

I largely agree with all that, but we have yet to discover how small (both physically and in terms of power consumption) eric's 'e-bike tyre pump' actually is.

There are plenty of 'cordless' bike tyre pumps around, usually with 2,000 - 3.000 mAh batteries, that claim to be able to do 'multiple inflations on one charge'. To my mind, that opens the possibility that the pump (that eric apparently already has) might be small, light and with low electricity requirements - in which case, if he is travelling with a 48V battery, using that to power his pump (maybe just via some resistive something) might make some sense.

Kind Regards, John