Charger circuit to replace Alkaline D-Cells with NIMH AA cells

[Ponchojack]

So here's the challenge...........

I have a Grundig radio that uses SIX D-Cell alkaline batteries. A somewhat pricey affair to replace these things when they run out. I can't blame the radio, it sips power and the batteries last a long time. The unit also has a 9V wall wart adapter.

What I want to do is replace the six D-cells with six AA rechargeables using those plastic battery adapters. I have no doubt it will work fine and the batteries will last a respectable amount of time.

I guess I could take the AA batteries out and put them in a charger when they run down, but what would be the fun in that?

No, I want to have the unit recharge the batteries while the 9V adapter is plugged in. Even one better, use a 12V source or adapter.

The challenge is what circuit is required to do this correctly?

Any takers out there for this challenge?

Poncho

[Ponchojack]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

A first thought.....what about using this smart charger? https://www.banggood.com/Black-Ni-MH...p-1640958.html

Then rewire the EXT power plug in the radio with zener diode to limit voltage to the radio circuitry while the adapter is plugged in charging the batteries.

Will this work?

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

your first issue, will the radio run o.k. at 7.2v
because 6x1.5 = 9v but 6x1.2 = 7.2v

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

another option is to use a couple of 18650's with a BMS board and a TP5100 charger board to recharge them from 9-20v input

[sam_sam_sam]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

another option is to use a couple of 18650's with a BMS board and a TP5100 charger board to recharge them from 9-20v input

To me this would be a better option
Than this

A first thought.....what about using this smart charger? https://www.banggood.com/Black-Ni-MH...p-1640958.html

Then rewire the EXT power plug in the radio with zener diode to limit voltage to the radio circuitry while the adapter is plugged in charging the batteries.

Will this work?

Here is the reason why I have not had very good success use this type of charge
First problem is that if want a charge indicator ( LED light ) it messes with the circuit sometimes it does not matter that use one is used or not the charge curve are shit with this type of chargers to being with any way

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

this is reasonable,
it will charge in 10 hours with ikea 2400ma AA's from a usb cable!
https://www.banggood.com/1-8S-1_2V-9...p-1625308.html

[budm]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

The bad part of trying to charge batteries connected series, you can have bad cell, I.E. shorted cell or open cell, and not all the cell will have the same cell Voltage.
I would try with 18650 and TP4056 with protection feeding a boost converter.
http://www.icstation.com/5pcs-micro-...e-p-12734.html
But you will have to watch out if those converter may cause interference issue with radio reception.

[eccerr0r]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

had lots of devices using packs of NiMH/NiCd/Pb in series back in the day and nobody complained...

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

nobody complained till they leaked anyway!
having said that, even after about a decade, nobody on any forum has seen an eneloop leak!!

[Ponchojack]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

Thanks guys fro the quick replies. On the 1.2 vs 15 volt issue. This should not be an issue. Most devices are designed to handle it since traditional D-cells will drop from 1.25 to 1.0 volts over their lifetime. The device is typically designed for the 1.2 volts. NimH tend to frun flat for most of their power curve.

I'm assuming the the 18650 idea would use 3 cells with buck regulator?

I would need to look into the charger. Also not sure how to do the physical fit. The nice part of AA batteries, they make cheap converters to fit. The batteries are easily removed for checking or replacement if one goes south. I've not had to deal with isolation issues before, will the idea of a Zener diode work?

[Ponchojack]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

The TP5100 idea is interesting especially if the radio will run on 2 18650 cells. I'll have to hook it up to my PS and see hoe well it works at 8.4 volts

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

7.2v, not 8.4
8.4 is fully charged, 7.2 is average.
and 5-6 is considered depleted.

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

I'm assuming the the 18650 idea would use 3 cells with buck regulator?

i was thinking 2 cells in series for 7.2v directly connected with a bms/protection board, and disconnected via the switch in the power-jack when charging (via an internal TP5100 board between the jack and bms)

[Ponchojack]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

Stj, thanks for the good idea. I'm going to try it. I'll let you guys know how it goes.

Poncho

[sam_sam_sam]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

One option would be to use 18650 batteries that have a buck converter built in them but they are a little pricey but you do get decent run time out of them but you would need the adapter change them from AA batteries to D size

[stj]

Re: Charger circuit to replace Alkaline D-Cells with NIMH AA cells

NOOOooooooo...

any buck/boost convertor in a radio will trash the reception!