Battery Charger

Hi Melissa

Is it because you want to charge the individual cells?

/Glenn

If so - do you have other batterypack criterias?

/Glenn

I am charging a 3.7 V 1200mAh LiIon battery. I want to isolate the AC to DC adapter because of safety issue.

melissa

The ac to dc adapter should have adequate isolation. Is that not good enough?

/Glenn

What are you doing that you need more than the several thousands of volts of isolation provided by the charger?

The wart looks fine. It's already isolated.

I am trying to provide user more protection. The other thing is that its an interesting problem to solve. But I do need some direction here.

melissa

More than what? There's some common test protocols, and models of human-body load, involved. If you want an UNCOMMON test or model, it'll cost ya.

Easiest way to provide 'user' more protection, of course, is to use connections that the user doesn't come in contact with. My electric toothbrush charges by proximity, not an electrical contact anywhere you can see or touch.

snipped-for-privacy@gmail.com brought next idea :

Wots your REAL problem? ;-) Or do you have so little knowledge that you cannot describe your real problem?

There is no relation at all between the 2 data sheets you quote.

One plugs directly into the mains and the other only uses the already isolated supply within an already certified device. :-?

I was told by a collegue that this is a challenging problem. i took sometime and tired to figure out but could not figure it out. You can take the AC to DC adapter out of the picture and use a +5v power bench power supply.

Please explain in detail what makes it challenging.

Please explain what level of isolation you are seeking.

Please quote any specifications you must meet.

Best would be if the OP describes his real problem then we could maybe offer some ideas.

John S and John G are not the same person even though the agree at this point. lol

Ahh!! but what isolation does the bench supply have ??? (Hint like the wall wart? ).

Hello, Could your colleague specify where the challenge is ? Most wall warts and bench power supplies use the standard step-down transformer->bridge rectifier-> capacitor bank->voltage regulator/overvoltage protection design. So the isolation is there right at the start. Is there anything special - a biomedical device with some special requirements ?

Iron transformer adaptors, with Class 2 or Double Insulation, have a long track record of being exceptionally safe - the same cannot be said for most of the switching types pouring out of China.

Another idea is to change the plug on the output cable to a non touchable kind - but it cannot be any connector that is associated with AC power.

You have not indicated whether the imagined " safety issue " originates from the adaptor or the battery side of things ?

... Phil

The wall wart she picked is a switcher. Actually most modern wall warts are switchers these days...for better or worse.

It is certainly possible to add a second DC/DC with isolation, but that is a lot of work for a dubious return on investment. It would most certainly reduce the efficiency.

I suppose if you really didn't trust the wall wart peddlers, you could go AC on the output. Then all the peddler is supplying is a low tech transformer and some sort of short circuit protection element.

Hi Melissa

Please read:

The "old" way is to use a 50Hz or 60Hz insulation certified (5000V) transformer. E.g. the transformer could have the primary winding separated from the rest of the windings on the bobbin. Combined with a linear regulator this is normally a very robust solution, that works for decades.

The "new" way is to use a insulation certified (5000V) high frequency transformer in some SMPS circuit. The problem with these is that the designer or component-buyer sometimes use bad capacitors or bad designs (incl. to little filtering) so they to often fails prematurely. The most used way of signalling back from the secondary circuit the primary circuit is to use an optocoupler that can 5000V (most can). The good thing about SMPS is that they can be efficient. Some can even use almost zero power from the grid when not loaded on the secondary side.

Another way is to transfer the power wirelessly. There is ongoing research and development to make this a public reality. The area has of cause been littered with patents.

Please note that the primary to secondary circuits must also be insulation certified (5000V).

Anything that bridges (e.g. noise suppression capacitors) between primary and secondary circuit must withstand 5000V.

Note that the term isolation transformer (e.g. 110V->110V - or

-

October 27, 2012, A dozen USB chargers in the lab: Apple is very good, but not quite the best:

USB Power Supply/charger Test:

February 12, 2013, Teardown of a HomePlug Adapter:

5kV HIGH VOLTAGE DIGITAL INSULATION TESTER WITH SOFTWARE & USB:

Professional insulation meter with test voltage programmable up to 10kVDC:

Fluke 1550C Insulation measuring device, 250 V - 5 kV Manufacturers guarantee 3*:

Comparison table - insulation measuring instruments:

Back to Basics: Voltage Regulator ICs, Part 1 There are two basic types of regulator ICs, linear and switch-mode. The linear regulator operates in the linear region and is always on, whereas basic the switch-mode type turns on and off and requires a rectifier to produce a dc output voltage.

Back to Basics: Voltage Regulators, Part 2. In this second part of the Back to Basics series on regulators, we examine buck (step-down) and the boost (step-up) forward and flyback topologies, as well as the SEPIC, hysteretic and multiphase converters.

Off-Line SMPS Failure Modes PWM Switchers and DC-DC Converters

Badcaps.net - What Causes This:

How-To Repair a Desktop LCD with Bad Capacitors:

7 June 2007, Wireless power a reality:

Dec 12, 2012, Magnetic metamaterials could boost wireless energy transmission:

DIY: Wireless Battery Charger:

/Glenn

On 18/07/13 10.14, Glenn wrote: ...

...

The above links are only for signal transmission - not for power - sorry.

/Glenn

One more link:

May 19, 2012, Apple iPhone charger teardown: quality in a tiny expensive package:

/Glenn