Universal battery pack

[Desertprep]

I am putting this question in this forum, first of all, because there are a lot of battery guru's here...secondly, because it is going to be something that I will use with my ebike on my "stress rides", i.e. rides out away from the beaten path into the undeveloped areas. I would also like to have the option of running my lights off the battery pack instead of the bike battery at night. I went shopping recently for a battery pack that I can use to charge/power my cell phone, mp3 player and, soon to own, tablet pc. The largest one that I found was about 2 amps, was the same size as the battery for my notebook pc and cost $150. Has anyone seen a set of plans for a DIY battery pack? I need 12v and 5v (USB) My gut feeling is that $150 should be able to buy the parts to make a 5 amp battery pack. Any ideas?

 

[Kin]

Hey. So uh. Hmm.

To be honest, I don't understand what you're saying (i feel like I post this a lot as a preface to everything I write here.)

You start off talking about running your bike lights off of your ebike battery. Yes! That is doable. You want to look for a dc-dc converter that's capable to deal with your bike's max battery voltage, gives you the right output voltage, and can output enough current to run the lights. depending on what lights you have that's between a tiny amount to a medium amount. They're very abundantly available on ebay though, and for a good price.


But then you talk about making a battery that can power a 12V netbook pc and a bunch of 5v devices. Assuming the 12v devices draw the most power, this is very doable. But it's a bit tricky. First, make sure your device actually only needs 12v, and can't tolerate more than 12v. For example, my laptop has an 11.1v battery, but that means the max voltage is 12.6v, and on top of it my input power is actually 19v to the charge port (seriously? What happens to all that extra power? I have no idea if it's just thermally dropped or used intelligently.)

But once you know really exactly what you need, you can start to figure out how to put together your own pack. Most likely if you need 12v and 5v, you'll want your battery set for 12v output and also have a $5 switching regulator that can output for the 5v line with very few losses.

 

[cal3thousand]

If you don't want to run off the bike's battery pack, then a small 3S or 4S pack would probably be what you are looking for. Then, a small DC to DC converter to take the 12-16V down to about 5V for the USB circuit.

If the components that you are attaching can accept a slightly higher voltage, go with 4S. Otherwise, 3S and keep them topped up at 4.1V to stay above 12V.

 

[dogman dan]

Maybe 3s lipo for the 12v. then put a cigarette lighter plug on the 12v. the lighter plug can then use a cigarette lighter usb port to get that voltage.

 

[Kin]

If you're pulling a lot from the cigarette lighter (5v), then you don't want to use it. The ones I've seen are linear regulators, so they waste 60% of the energy they deliver. The good part is that it doesn't matter that you'd be feeding it 12v nominal, even though cigarette outlets are really 14v while the car is running. But if your 5v line is a small percentage of your 12v line, it's an ok cost. But if it's any substantial amount of your pull, it's a waste of energy to use a linear regulator instead of a $4 more switching regulator.


The key thing is that you need to define what you ACTUALLY need. And the OP hasn't made a response on that.


*Disclaimer, when I say the 5v usb car outlet things I've seen are linear regulators, that's because I'm a cheapo and buy the $3 shipping included ones from Ebay (i.e, from HongKong / Schenzhen . Perhaps the $15 ones at electronic stores / non cheapo locations use a switching regulator.

 

[dogman dan]

My assumption was the usb was to keep a smart phone topped up, or run an ipod. Maybe keep a go pro going longer.

 

[Desertprep]

Thanks, and sorry for the ambiguousness.

Purpose of the battery pack:

1. Recharge MP3, cell phone, digi camera, and tablet.
2. Backup to power ebike lights when I am reaching the depths of the battery on the bike.

 

[Kin]

If I understand you, that you are considering a second battery in addition to your bike's battery, and that second battery will run bike lights and occasionally charge peripherals like laptop/mp3 players, then I believe that:

You're better off getting a bigger battery pack for your bike. You can run cheap DC-DC buck converters to take your pack's voltage and make 12v and 5v on demand.