uCurrent Gold with external power....

[ammjy]

Hello guys!

First, Please, understand my English. not so good.

i want use uCurrent with external power. so, now i'm doing make custom circuits based uCurrent Gold circuit in KiCAD. if i done, it will have 2-way power.

and i found something important one. that is power source should be isolated. so, Mr. David jones use battery power source. so, that simple circuit can measure precision current.

but, i want use external DC power(like USB). i want escape from battery life time so much!

so, i choice MAX256 IC. this IC work like this. [ Input 5V and make AC source by inner FET. and make DC Voltage/Current by transformer, LDO parts. ]

it will be no problem?

and if i use MAX256. necessarily, it will generate noise. and problem is CAPs can't remove noise perfactly. it's very big problem..
maby, in bad case, uCurrent measurement accuracy will going down to earth core or going to Andromeda Galaxy.

Somebody help me! i need a Idea and advise.

my chat nickname is Kall.

[nukie]

Why dont you install a 2000mah battery from a mobile phone? I only have to recharge mine once a year of heavy usage. Ie leaving it on most of the time.

[Chalcogenide]

+1 on the idea of a rechargeable lithium battery. For charging, a cheap TP4056 module from China is good enough and if needed you can also power it up from an external USB battery bank. If you want a constant voltage then use a low quiescient current 3.3V LDO (but I don't think it's needed at all).
If you absolutely need to supply 5V to increase the dynamic range of the uCurrent, then you could use 2 batteries in series and an LDO, but then you would have to charge them individually or use a proper balancing circuit.

[SeanB]

99c USB power bank and 18650 cell will work, and you just remove the boost converter side leaving only the charge controller. That way low noise, and the uCurrent is going to last a long time on the 18650 cell, especially if you decrease the led current to 500uA.

I see I have a spare Lumia battery pack around, so when the postie drops off the power banks in a few weeks in it will go with the slighly modified pcb to replace the CR2032. 600mAh will work for a long time, just have to plug it in once every 6 months.

[Jeroen3]

External power only adds noise. Just use some alkaline cells.
Unless you need to measure for months continuously.

[RobertBG]

External power only adds noise. Just use some alkaline cells.
Unless you need to measure for months continuously.

I used to think like this until I had to live abroad on a locals salary and believe it or not batteries cost can add up.

I second using a rechargeable battery sourced from a old cell phone etc.Unless you are going to be running it nonstop in a application a rechargeable battery is going to be the easiest route.I've salvaged portable home phone batteries and charging circuits for quite a few things like this.It is very easy to modify and use the charging dock to keep things that you use often charged and I find the NI-MH batteries tend to do better then cell phone batteries if you are going to use it and then throw it back on charge.I actually converted my TV remotes this way and haven't had to change a battery for years

[ammjy]

Why dont you install a 2000mah battery from a mobile phone? I only have to recharge mine once a year of heavy usage. Ie leaving it on most of the time.

Thanks advise!

i thought already battery. but, i want just externel power.

[ammjy]

External power only adds noise. Just use some alkaline cells.
Unless you need to measure for months continuously.

yes. i agree that. external power add noise. but, i will try remove noise.