Rechargable Batteries

Invent-O-Doc

I have a portable project that needs about 6Volts. I note that the cases I want to use require (PAC-TEC) require a very large order to get them with a 4xAA door and housing, but the default 9V battery housing will leave me with not enough longevity.

If I got a Lithium or NiMH battery and glued it into a case. How would I hook it up so that it can be recharged when the unit is plugged into an external DC source such as a wall-wart?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

---

Thomas Talbot, MD
Gunpowder, MD, USA

SRLM

You could put in a switch so that it turns of both lines to the electronics, and have some extended cables to whatever part of the case that you want to connect the charger to. Just make sure that you remove the charger before you turn on the device.

If you want a charging circuit, then do a search online. Here are two that I found:
http://www.coolcircuit.com/circuit/charger1/standalone_nimh_nicd_charger.html
http://www.angelfire.com/electronic/hayles/charge1.html

Some more information might help get a better response.

Invent-O-Doc

Sure I can give more detail. I have a project that needs about six volts, though i am using a single 9V battery now with voltage regulators (5V and 3.3V) Since the 9V doesn't hold a lot, I though having an internal nonremovable battery pack would make things simple, either Lithium or NiMH. The battery must be at least 6V. The power switch is DPDT, so it could be used to reroute the batteries from the circuits to a charging connector.

My question is: Is there a simple way to do the charging by plugging some DC into my device, or if that would be too complicated, would it be easier to hack a battery charger so I can charge the batteries without removing then from my project case?

I have seen some schematics online, only some appear practical. The best that I found was based upon two LM393s and a thermistor. I'm beginning to think that it might be better to use an R/C universal battery charger.

At this point, I'm mainly wondering what other people who have made projects that rely on a rechargeable battery have done.

Thanks!

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

---

Thomas Talbot, MD
Gunpowder, MD, USA

RDL2004

Be careful when going to rechargeable AA batteries from the 9 volt cell. Check your regulator's specs for "drop-out" voltage. You may need to change to a LDO (or Low drop-out) type of regulator and/or go with 5 or 6 rechargeable AA cells in order to maintain regulation. Be aware also that NiCad and NiMH cells are only 1.2 volt.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Rick

uxorious

This is a topic that has been on my frustration list for 2 years. I am constantly wishing for a simple 6 volt rechargeable circuit for my projects. All of the schematics I have seen are in the 20+ part count range which equates to "not-simple" in my mind. I am working with a colleague actually to create a 6 volt battery back with built in charging circuit. We have a design from another project that's for a Li-Ion battery (it's 1/4" thick 5"x7" and rated at 7.4V, 1.4A, so it won't work for handheld apps). We are working on the battery make-up now with a Chinese supplier to finish it off. The PCB will be made stateside. We have a couple other projects in front of it, but it's still active for us to finish it.

Not sure of the size of the case you are using, but check into Polycase. (polycase.com)

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
~~ dRu ~~

Erik Friesen

Why not use 2AA's and use a tps61070 step up converter to 5v and a 3.3 ldo?

The parts add up to $3-$3.50 I think.

The simplest charger you will find is going to be down the RC charger line. If you charge more than that you will need some sort of charge detection circuitry.

2AA's at 2500mah = 7500 mwh 1 - 9v at 170mah = 1530 mwh. No comparison in rechargeables.