Next to Last Word Power Supply

[cachenut]

Hi Guys:

I put together other peoples comments and came up with a description of the problem for me.

Some engineers told me the detector runs on a recommended voltage of 12 volts. It can pull 1.5 amps briefly at startup but runs normally on .11 amps. When it sees a target it goes up to .13 amps. Use the backlight and it is .3 amps. Another engineer said it ran at .10 amps when idle.

I understand better now due to the answers I got. Thanks. Amperage is not important unless underpowered. 1.3 amp hour battery is just fine provided it gives 12 volts.

I found a sealed wet cell on the internet that generates between 12 and 13 volts and is a 1.3 amp battery for 20 hours. It is advertised as a 12 volt battery but the data table they have show it starts at 13 and drops to 12 after a while when fully charged. I expect in practice it will be closer to 12. One of my engineer friends wrote back to say 13 volts would do fine in the explorer and he would know.

So I think I will be safe at 13 volts and a little less. Another person says he uses a 14.4 volt gell cell for his minelabs all the time without problem. I dont want to push it, just fully power the detector.

So I plan to order the battery and try it out. My first attempt will just be to get it running. If it works I will modify a battery pack to make it more permanent. I thought a plug in connector for power in the back of the battery pack like the headphones would be nice.

I plan to use regular auto wire for the first try. Is there some sort of 2 wire cable that is small and good for DC. How about very small plug in for current?

They also make all sort of chips these days. Radio Shack has a 12 volt regulator chip that puts out 12 volts for up to 37 DC volts input. This would solve the problem in a more general way. Cost was $1.69 cheap. Just plug one of these into the circuit and I've got it made. I even saw one glued to the side of a battery once with the wires soldered to it. It was inside a UPS power supply.

If you know about dc plug in connectors, volt regultors or wire please let me know.

As for the extra depth problem I am not so sure I will get extra depth except when the detector is underpowered. This may occur after 10 minutes or 2 hours I am not sure. I would prefer to be fuly powered all the time since I put a lot of time into finding stuff and dont want to miss just cause of a weak battery. And there is cost. The battery will cost $7.95 only. The whole set up will cost less than the batteries I buy in one year.

 

[Captain Kirk]

Cachenut,

* 0.100A is the same as 100mA.
* 1500mAhr means that the battery can supply 100mA for 15 hours before the battery is depleted. But greater current draw tends to reduce battery capacity. Therefore, if the battery load is 1.5A, then you will probably get much less than a 1 hour operation before battery depletion.
* Review page 92 of the Explorer II manual for the NiMH battery . You will note that the battery voltage fall rapidly for the first 2 hours. Then there is a flat portion of the discharge curve for the next 8 hours. During the final phase the battery voltage falls quite rapidly until the battery is depleted.

Personally, I have not noticed any difference in performance of the Explorer II whether the battery is fully charged or near depletion.

Hope this is of some help to you.
Glenn

 

[Charles (Upstate NY)]

If one is thinking peak voltage = peak depth e.g. they are somehow getting less depth when the battery meter reads 50% note that I have had Explorers on an oscilloscope with batteries at full charge and run them down to the point the Explorer shut itself off and there is no change in the transmit signal strength.

Some things to consider...

1. The original Explorer rechargeable batteries are only 9.6vdc, while the alkaline pack for the same machine yeilds 12vdc. The machine can clearly pull deep coins with the 9.6vdc pack, I have dug them.

2. This also tells you it can tolerate an operating voltage range of at least that 9.6vdc to 12vdc. I think Minelab very likely would have built in a safety buffer of a couple volts minimum since peak voltage with fresh batteries can exceed 12vdc.

3. The transmit signal strength is not variable, no setting you can adjust via the menu will change the transmit signal strength.

4. With voltage regulators one can do all sorts of things with a single 9.6 or 12 volt power supply. Double it, divide it, regulate a specific voltage. One could create several supply rails, many electronics components are rated 5vdc. Some LCD screens require 18vdc. Transmit circuits may run +5vdc to -5vdc. All using a single 9.6vdc or 12vdc power supply.

5. Before you think about introducing an additional regulator keep in mind that you may be generating a source of noise in the circuit. Noise is an issue when you consider how pitifully small the recieve signals are. I have noticed that simply turning on the backlight will make my machine somewhat unstable in certain situations.

6. There is more to depth than voltage. One can go high voltage low current or low voltage high current or some balance inbetween.

All that said what you can do with a custom power supply is run the machine longer on a single charge. I have run 10 cell AA packs of nmhd rechargeables yeilding 13+ volts. I know someone who has run 10 cell AAA rechargeable packs for years on his Explorer. He only gets about 6 hours on the pack BUT the reduction in weight versus a AA pack is huge!

Just my two cents worth.

Charles

 

[migolddigger]

OK 1.7 volts x 8 = 13.6 volts. OXY's, Enlope, thats all I'm gonna say about it. Maybe you guys didn't hear me the first time. That is what I got from Minelab directly and what they are recommending for the Explorer at this time. Better operation and better depth. I don't care about if it last 6 hours or if it last 12. I want Quality performance time, not long time poor performance. The output is stronger with stronger voltage batteries. It's pretty simple to me.

Tom

 

[cachenut]

Thanks Charles:

Informed opinions are always welcome. And helpful.

I may not get better performance if any. Will see what I think. Of course the batteries will be cheaper. Maybe $25 to set up the alt supply and it will be good for the life of the detector. No more down time in the field cause I don't have good batteries and no more chasing around for the ones I like.

I myself notice a difference in performance when batteries are low but I cannot say for certain that a higher voltage or amperage will increase performance. I believe it does.

Thanks for the comments on the voltage. Someone said 13 volts would damage my explorer for sure. I too expected Minelab would design the things right and provide some cushion on voltage just to be on the safe side.

My battery is rated at 12 volts and I hope it delivers close to that all the time. So hopefully I would not need an extra voltage regulator. They seem to be cheap at radio shack if needed. I had not thought of the noise.

I also need to watch switching the polarity so I think I will get a couple of two wire connectors that go together only one way and stick one on each end to prevent this. And watch the cable for any nicks and bare wires at solder points.

thanks.

 

[cachenut]

Thats pretty much my attitude. If I am going to spend hours of my time searching I want to be SURE I get the best response from the detector that I can. I do think new batteries make it work better.

Someone in the know told me that the new Lithium ion batteries that ran at 13 plus something for 8AA would damage my explorer for sure and they were not recommend. This bothered me. Even said it was in the new SE manual not to use them.

I will be happy with a consistent 12 volt supply.

Thanks for your response. I'll let you know after I get it done.