electrically inclined people - could you help me?

[zband]

I have a boom box that I am should run off of 6 d-cells. The voltage needed (on the boombox ) is 9V and 20W. I would like to run it using nimh rechargeable batteries but here is the problem- I dont want to spend the $ on them if they are not going to work.

I have 6 old duracell batteries each one shows a voltage of 1.45 V (except one - 1.32V) The voltage coming out of the pack is measuring 8.4V and the unit doesnt turn on. Is this because the total voltage is too low -or - the batteries cant make the amps?

Because if my goal is to use rechargeables then the total would come to 7.2 volts (6x1.2v), which is even lower than what my old duracells are putting out so, at least in my non-academic mind, rechargeables wont work.

Any clues, or insight would be greatly appreciated!

 

[Mr Happy]

the total voltage is too low?

No.

the batteries cant make the amps?

Yes.

To get a good feel for the health of a battery you should measure the voltage when under load. Connect a bulb to it while measuring, for example.

 

[zband]

So the unit is not turning on because the batteries are possibly not suppling the proper amps and its not the voltage ?

That being said, do you think I could run it on NiMh D-cells even though total voltage would only be 7.2 volts ?

 

[Mr Happy]

Yes you can run off NiMH D cells. It is a myth that alkaline batteries provide 1.5 V.

Incidentally, you should check that the unit isn't broken by making sure it works with good batteries.

 

[Glasstream15]

I have an old (1997) Aiwa boom box that takes 8XD batteries. It runs great on Rat Shack 4500 mAh NiMHs. And a Sony (2003) 6XD that also runs great on the same rechargeables. And just about equal run time as primaries. A/C power cord has better run time than any of the batteries though.

 

[paulr]

Zband, your box will work fine with rechargeables.

 

[zband]

Thanks so much for your responses. I picked up some cheap d cell - just to see if the box worked. It did not. Something is burned out on the circuit board.

So I tried to find an electronic repair shop. Can you believe it- 10 years ago they were everywhere- today - they are extinct! We've become such a "throw away " society!

 

[Darkpower]

Thanks so much for your responses. I picked up some cheap d cell - just to see if the box worked. It did not. Something is burned out on the circuit board.

So I tried to find an electronic repair shop. Can you believe it- 10 years ago they were everywhere- today - they are extinct! We've become such a "throw away " society!

It might be cheaper to buy a new one.

I've got a large RCA boombox that runs on 6ea. D cells and 3ea. AA (for memory functions). That thing used to eat Alkalines for lunch. It does much better on NiMh. In fact I bought the Accupower LSD "D" for it at a cost of $12 ea. The batteries are worth more than the boom box but I no longer have to feed it $6 worth of batteries after one or two weekends of play (maybe 8 hours). I use the boom box for the patio on weekends and radio talk shows during the week.

Anyhow, the boombox used to quit working when the alkalines reached 1.15 volts which is really only 2/3 discharged. On the other hand, the NiMh run the box until they reach about 1.05 volts. I get more hours of play time with the NiMh for about 10 hours, but unless you use the boom box continuously, normal D cell NiMh may self discharge faster then you will use the boombox if you are an occassional weekend listener which is the reason I went for the more expensive LSD batteries.

Also the current drain is fully dependant on the volume setting. The NiMh can deliver strong bass sound and high volume without shutting down at peak volumes. When I used the alkalines, the radio would shut off if the batteries were near the end of life and the volume too loud and if a sound came out causing it to produce deep bass sounds. Then I could restart it by reducing the volume. But the NiMh, it works all the way to the fully drained voltage.

 

[zband]

The more I read and learn about batteries (LD NiMh) the benefits are truly astounding, too bad my box is not working. I would love to try out some D-cells on my new 808 charger!

 

[MrAl]

Hi there,

Sorry to hear about your bad boom box, i hope you can get a new one for a good price.

About using the NiMH cells...
Usually they work too, but if not sometimes adding another one in series helps, although
you have to watch out for the max voltage when they are fully charged, that it doesnt
burn out your device.

One example where the NiMH cells wont work very well is in a fire alarm.
The voltage drains down to 7.2 too fast and the alarm would beep.
Adding another cell in series might help, but it could also burn out the device
when the cells are freshly charged.

 

[jayflash]

I did that very thing and added two more D NiMH cells to the eight alkies normally called for. There was extra room in the old briefcase size, 10 WRMS/channel, ghetto blaster I gave my wife for her old factory job. It played louder on the rechargeables than the, apparently wimpier, internal power supply. After years of abuse the old, discrete, bipolars are still cranking the dBs. Good thing for its heavy duty heat sink.

 

[Jarl]

*cringe*

Freshly charged a NiMH makes 1.4V or so. Under load this drops to about 1.2V, hence the 1.2V rating.

Fresh out the packet a alkaline makes 1.6V. Under load this drops- the larger the load, the larger the drop. Generally speaking, under small load, an alkaline at 1V still has about 50% juice still left. I don't know why they're rated at 1.5V. Someone obviously thought it was a nice number, and it stuck.

For some devices, such as a fire alarm, alkalines are needed. For other devices that require the internal resistance of the cell to keep current down, alkalines are also necessary. For everything else (i.e, flashlights, boom boxes, remote controls) NiMH will replace an alkaline with no loss in performance. Adding more cells will overvolt the device, potentially damaging it. To all intents and purposes, the two chemistries are exactly the same.

 

[zband]

I found an electric repair shop and in about 10 minutes the guy diagnosed the problem! A faulty "bridge" connector. I ordered a new one for $6. I told him that I am going to replace the batteries with NiMH and he said its not going to work. But I got a feeling that you guys know more about batteries than he so I'm off to find some LD d-cells. suggestions?

So the take home in this discussion (correct me if I'm wrong): alkaline batteries are rated at 1.5 volts but if the current draw is large, say 1 amp the voltage of the cells quickly decreases, while NiMh will maintain a 1.2V rating?

 

[shadowjk]

http://www.candlepowerforums.com/vb/showthread.php?t=79302
http://www.candlepowerforums.com/vb/showthread.php?t=64660

If you compare the graphs(AA), you can see that at 1.0 amp, alkalines drop below 1.2volt after approximately 12 minutes. Eneloop NIMH stays over 1.2 volt for more than an hour.

 

[JWP_EE]

Here is another good article on the 1.5V vs 1.2V myth.

http://www.eznec.com/Amateur/1.5_vs_1.2_Volt_Batteries.pdf

 

[zband]

A very nice find! I feel better about investing $80 in low discharge d-cells. Matter of fact I was just looking at the accupower 10000mAh one at thomas distributing.