Charging Nimh while using it.

[lumoro07]

Hello,

I am close to finishing my RPi portable, pretty standard stuff: a RPi, screen, battery and some buttons.
I want to connect my RPi and display to a Nimh battery pack (7,2v 5000mAh), but i want to be able to use te portable while it is being charged.

My setup right now uses between 450-550mAh at 7,2v, a 12v battery would be better but those are too big.

Can i just connect the load and battery both directly onto the charger? Won't it be better to separate the battery while charging so it doesn't have to supply current while it's being charged?
I tinkered around somewhat with the power circuit, trying out different configurations of diodes and whatnot but i cannot seem to find a way that fits my needs.

I intent to buy a Nimh battery pack and a wall charger to safe me the trouble of finding a place to buy a charging circuit (or making it myself).

I'm also open to other sugestions on how to power a portable.

[klricks]

Hello,

I am close to finishing my RPi portable, pretty standard stuff: a RPi, screen, battery and some buttons.
I want to connect my RPi and display to a Nimh battery pack (7,2v 5000mAh), but i want to be able to use te portable while it is being charged.

My setup right now uses between 450-550mAh at 7,2v, a 12v battery would be better but those are too big.

Can i just connect the load and battery both directly onto the charger? Won't it be better to separate the battery while charging so it doesn't have to supply current while it's being charged?
I tinkered around somewhat with the power circuit, trying out different configurations of diodes and whatnot but i cannot seem to find a way that fits my needs.

I intent to buy a Nimh battery pack and a wall charger to safe me the trouble of finding a place to buy a charging circuit (or making it myself).

I'm also open to other sugestions on how to power a portable.

Charging a Nimh battery is complex. The charging circuit must be designed to handle the proper charge rate for the number of cells in parallel and/or serial combinations etc. Proper charging requires temperature monitor circuit and must shutdown charging yet keep the device powered. There are several makers of charge conrtoller chips.
Google [Nimh charging circuit]

[lumoro07]

Hello,

I am close to finishing my RPi portable, pretty standard stuff: a RPi, screen, battery and some buttons.
I want to connect my RPi and display to a Nimh battery pack (7,2v 5000mAh), but i want to be able to use te portable while it is being charged.

My setup right now uses between 450-550mAh at 7,2v, a 12v battery would be better but those are too big.

Can i just connect the load and battery both directly onto the charger? Won't it be better to separate the battery while charging so it doesn't have to supply current while it's being charged?
I tinkered around somewhat with the power circuit, trying out different configurations of diodes and whatnot but i cannot seem to find a way that fits my needs.

I intent to buy a Nimh battery pack and a wall charger to safe me the trouble of finding a place to buy a charging circuit (or making it myself).

I'm also open to other sugestions on how to power a portable.

Charging a Nimh battery is complex. The charging circuit must be designed to handle the proper charge rate for the number of cells in parallel and/or serial combinations etc. Proper charging requires temperature monitor circuit and must shutdown charging yet keep the device powered. There are several makers of charge conrtoller chips.
Google [Nimh charging circuit]

Thanks for the reply.
What i don't understand is, how is a charging circuit different than a charger in the form of an wall plug, there's a charging circuit in the wall plug too. So the only difference between the two is that one is inside the case and the other is outside it. How would i know i can 'use' the battery and charge it at the same time with either of them.

[klricks]

The wall charger likely has only voltage regulation circuit. The actual charging control circuit is built into the device. Some battery packs such as for laptops have the thermal sensor built into the battery pack. Notice that there are more than 2 contact points on a laptop battery.
If you want to charge raw cells then you have to provide all the charging circuit functions yourself or use a charge controller circuit.
The datasheet for the cells you have will explain how to charge them. Also read datasheets on the various charge controller chips.

[lumoro07]

The wall charger likely has only voltage regulation circuit.

Hmm i don't think so, the wall charger has an extra little box attached.

This is what it looks like :
http://www.vapextech.nl/NiMH-batterijla ... -accupacks

Battery :
http://www.vapextech.nl/7-2-Volt-NiMH-R ... ck-5000mAh

I thought it would be a good choice to avoid a charging circuit, i can't seem to find a store that sells the right ones.

[Burngate]

NiMH cells are easier to deal with than any of the lithium-based cells, but still require careful handling.

As with NiCad batteries, you can charge them at a fast rate, until they near their fully-charged state. From then on, they need to be trickle-charged.
So If you want to fast-charge, you need to detect that condition - not easy.

If the load only takes a small current, less than the maximum trickle-charge current, then you could always charge at that current, and the battery wouldn't be damaged. With full load, the battery would get charged slower than with no load, but still eventually get charged.

However that pack probably won't accept trickle charging at the current the Pi wants to take out, so you will need to detect the Pi's current, and make your charger supply that current plus the pack's trickle-charge current.

[leon_heller]

You could use one of these power packs:

http://uk.rs-online.com/web/p/power-ban ... 3735303826

I use one with my RPi. I haven't tried charging it while it is connected, but I don't see a problem.

[pluggy]

You could use one of these power packs:

http://uk.rs-online.com/web/p/power-ban ... 3735303826

I use one with my RPi. I haven't tried charging it while it is connected, but I don't see a problem.

Which would be OK if the OP were using LiPo cells, but he's using NiMH which is an entirely different proposition. As already been mentioned NiMH aren't half as tetchy as LiPo but still need a degree of care. The controller is entirely different to LiPo.

[Joe Schmoe]

Which would be OK if the OP were using LiPo cells, but he's using NiMH which is an entirely different proposition. As already been mentioned NiMH aren't half as tetchy as LiPo but still need a degree of care. The controller is entirely different to LiPo.

But does it really matter?

Isn't this just another variation of "Do I answer the OP's specific question, or do I try to solve his actual problem?"

I.e., "The XY problem" …

[pluggy]

In that case a resistor and a diode would cut it for NiMH, but It wouldn't do LiPo any favours. If you're buying a lump of kit to do a job, it may as well be the correct lump of kit. You can light an oxyacetylene torch with a blowlamp, but I wouldn't buy a blowlamp to do it.

[lumoro07]

You could use one of these power packs:

http://uk.rs-online.com/web/p/power-ban ... 3735303826

I use one with my RPi. I haven't tried charging it while it is connected, but I don't see a problem.

I wanted to use a powerbank, but my screen takes 6v+.

But does it really matter?

Isn't this just another variation of "Do I answer the OP's specific question, or do I try to solve his actual problem?"

I.e., "The XY problem" …

Like i said in my original post, i'm oke with other sugestions. However, i'm not really comfortable with LiPo batteries unless i'm absolutely sure i can charge and use it at the same time in a safe way.

In that case a resistor and a diode would cut it for NiMH, but It wouldn't do LiPo any favours. If you're buying a lump of kit to do a job, it may as well be the correct lump of kit. You can light an oxyacetylene torch with a blowlamp, but I wouldn't buy a blowlamp to do it.

I'm curious how you would place that diode and resistor, i have tried everything i can think off but i can't seem to figure it out.

[3corey2]

i suggest buying a simple yard light opening it up and taking the board out, hook up your battery(replacing its battery) and hook up the batter to your pi as welland remove the solar panel replacing it with your charge port thing. you may have to replace the ristor as well, i had to. (depending on the power input you may need install a tiny trasformer and another resistor)

[lumoro07]

i suggest buying a simple yard light opening it up and taking the board out, hook up your battery(replacing its thripple A) and hook up the batter to your pi as welland remove the solar panel replacing it with your charge port thing. you may have to replace the ristor as well, i had to. (depending on the power input you may need install a tiny trasformer and another resistor)

Thanks, that's a good idea. The only problem is finding one that has a battery of atleast 7,4v and atleast 4000mAh. The screen cuts off at 6v so considering voltage drop 7,4v is a decent starting voltage. I don't think those yard-lights have that much juice but it's worth looking at.

[3corey2]

no no no, you are taking out its tripple a or whatever, and you connect your battery up replacing it... then you have 2 wires of both neg and pos coming off the battery, to hook up to both the charging chip device and the ras pi, and you have the resistors/transformers in place to keep the lil chip from exploding into flames.

[3corey2]

also those yard lamps can be found almost anywhere for just a buck or two. and by "your battery" i meant maybe a rechargable 9v.

[pluggy]

I'm curious how you would place that diode and resistor, i have tried everything i can think off but i can't seem to figure it out.

Its extreme simple charging, I've used it for batteries that are (very) forgiving about how you charge them. They are wired in parallel the resistor is to limit the current going into (and out of) the battery, the diode is to bypass the resistor on the way out to feed whatever its feeding. It only really works for trickle charging, and you choose the value of resistor to allow an amount of current that won't damage the battery in the long term.

Its extreme oversimplification, I've used it with lead acid gel cells. It will destroy LiPo and NICD batteries and probably won't do NiMH any good in the long term either.

[lumoro07]

I think the easiest solution for me is to buy a 12v powerbank, like this one (sorry, the page is not in english) :
https://www.conrad.nl/nl/tecxus-tp-1000 ... 51166.html

There's a comment confirming it can be used and charged at the same time. 10000mAh at 12v might even be a bit overkill since my setup uses less than 350mAh at 12v.