Excalibur Battery Questions...

[cabochris]

I just purchased three of those 2700 mah 9.6 V rechargeable batteries for my Excaliburs. I got them because the manufacturer said they will last much longer than even their 1500 battery and that is important because I travel with my machines. The longer lasting the batteries the better.

Those 2700 batteries look great and I installed them into 3 older gray SunRay pods, no longer made. The SunRay batteries were 1650 mah, but I heard there were some problems with them and SunRay ceased production. While I never had problems with those batteries, recently they seemed to lose charge quicker. So I got the new 2700s.

I charged up the 2700s and all 3 topped-off at 11.64 volts. That made me start to wonder about battery voltage? In an effort to learn more I called the battery manufacturer and asked how a 9.6 volt rated battery could power a 12 volt detector? It was tough getting answers I fully understood, but I was told that the 2700 batteries would charge up to 12 volts and power my Excalibur much longer than any other! And that the 2700 battery held the required voltage to run the Excalibur longer. I was told the Excalibur can run on as low as 8 volts??? They must know what they are talking about? They also said they have sold many of these 2700 batteries to satisfied Excalibur users.

It just seems confusing to me that a 2700 9.6 volt battery will last longer then a 1500 12 volt? Those 1500 batteries charge up to some 14 volts. What is the minimum voltage required to fully run an Excalibur? Also, does the higher voltage equate to better detector performance? Or is having just enough voltage to run detector all that matters? Finally, what is battery discharge rate? The discharge rate of the 2700 batteries is much lower than with the 1500. Is there a battery expert out there who can explain this stuff better for me?

Thanks, CC.

 

[otlew]

Below is a link to a website that will answer your question.

Here is an excerpt from the site:

Can NiMH batteries be substituted for alkaline batteries even though they are only 1.2 volts?

Yes, for most high drain electronic applications NiMH batteries are ideal substitutes and you needn't worry about the apparent voltage differences. Even though alkaline batteries are rated at a nominal 1.5 volts, they only deliver 1.5 volts when they are fully charged. As they begin to discharge the voltage of alkaline batteries continuously drops. In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. That's very close to the 1.2 volts of a NiMH battery. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for most of their discharge cycle.

Batteries

 

[Critterhunter]

Exactly. Also, look at it this way. The machine requires a certain voltage to run. Thanks to a voltage regulator any higher voltage is ignored and actually wasted off as heat in a linear regulator, so providing more voltage than needed does nothing and actually is worse for the machine than a lower (but still within specs) voltage. As far as capacity goes, the higher the capacity the longer the machine will run, but this does nothing to change the amp draw of the machine. If it wants to draw say 1 amp then hooking it up to a car battery doesn't change that. It will still only draw 1 amp regardless of the size (capacity) of the battery. Bottom line is so long as those packs provide at least the mimimal voltage the machine requires it will run it just as well as say a 12V regular store shelf 8AA pack. The 1.2V per cell nimh/nicad rating is just a general guide line. They will charge higher than that. And 1.5V store batteries will soon be lower than a good nimh or nicad because they don't have as much capacity. Put a 2500ma AA or higher into a device and it will out run a normal store battery.

 

[cabochris]

Critterhunter, Thanks for helping to clear this up for me. What you say is starting to sink in! Oh, I totally agree with your Signature!

 

[cabochris]

Yes, this site has good battery info, thanks. It will be interesting to find out what the minimum Excalibur voltage requirements are? Hopefully Minelab will respond to my emails.

 

[Critterhunter]

It probably is around 10.5V like the GT. Once it dips below that the regulator can no longer work properly and the low battery alarm will kick in. Dig up the "Excal Battery" thread for in depth info on batteries, chargers, etc. It's a huge thread with many pages.

 

[John(Tx)]

Would it be ok to install these 2700ma batteries into my excal alkaline battery pod and use the excal charger to charge them while in the battery pod? Thanks, HH

 

[cabochris]

The manufacturer says yes to both your questions. I'm off to the Caribbean for a week to shallow water treasure hunt and will find out just how long the 2700 batteries last/perform. When I return, I'm going to look into other battery builders and see if they can make a rechargeable 2700 battery with 1.5 volt cells? CC.

 

[synthnut]

I just slid one of my 750 m.a. Lipo's in my Excal 's Alkaline pack ....Nice and light weight , and I can hunt all day with one charge ....If it's gonna be a long day, I bring an extra along with me .....Lightweight, cheap , and easy to charge with my Accucell charger .....Binga , Banga, Boom !!!.....Jim

 

[kered]

Quote CH
" Thanks to a voltage regulator any higher voltage is ignored and actually wasted off as heat in a linear regulator, so providing more voltage than needed does nothing and actually is worse for the machine than a lower (but still within specs) voltage."

Now thats interesting i have opened every detector i have owned, non of the components get remotely warm, according to a minelab engineer the voltage is converted to a usable voltage(i'll look for the video and his explanation of how it works). I don't think any manufacturer would produce over voltage batteries if it was a waste of time and worse for the detector.
To boot if a detector used 9.6v and you put in a 12v battery it would last as long as a 9.6v battery if its as you say they just burn off the overvoltage as heat, to me it just doesn't add up to comon sense, what is the point in doing that.
The way i understand it is the 12v is taken and converted down to the voltage used by the detector, to get 9.6v(minelab etrac voltage) from a 12v battery the draw is small, therefore the battery lasts longer, as the battery gets down the voltage starts to drop faster until a point when things are even 9.6 baterry 9.6 needed, the voltage regulator from then onwards needs to produce the same 9.6v from a lesser voltage and so the battery drops of fast, in effect that is what happens on the etrac, i have measured the battery imediately the detector cuts of and its in the region of 8.6-7v, the GT is as you know higher voltage cutoff as as far as i know the detector uses 12v.

Looking at things from another angle, if the voltage regulator only burns off excess once the 9.6v was reached the detector would cut off or performance will diminish as the detector is not running on a full needed voltage could be why some people say the detector runs better on full batteries, although my car doesn't run better on a full tank of gas than half full i think my detector doesn't either, maybe on cheaper makes it does.

 

[John(Tx)]

Thanks for the info, I will give them a try. A week of water hunting sounds like fun especially down at the Caribbean. Have fun and I wish you alot of success, let us know what you find. Good luck. John

 

[Willee - Texas]

There is a relationship between voltage and current.
The battery's are rated for the CURRENT they can deliver over time.

A 2700 Mah rated battery pack can deliver 2700 ma for one hour.
Or twice that current for 30 minutes.
Or half that current for two hours.
Or one quarter of that current for four hours.

Get it?

If your detector needs 20ma for it to operate then a 2700 Mah pack will supply that current for (2700 divided by 20) 135 hours.
(under ideal conditions)
So it stands to reason the larger the capacity of the battery pack (Mah) the longer it will run your detector.

There is a chip in your detector that regulates the battery voltage down to the level required by the electronic components.
That voltage is somewhere around 8 volts or less.
So you see that the voltage drop of the battery over time is not really important unless it drops below what is required by the electronics.
As long as the detector can get its full current requirement supplied it will work but once that current starts being cut back ... due to low battery voltage ... the detector starts to shut down.

BTW: A resistor works by converting electrical energy into heat ... and your detector is full of them.

 

[otlew]

Good job Willie. I thought about doing a hydraulic analogy, but no need now you nailed it.

 

[Critterhunter]

There are two types of voltage regulators that I'm aware of. One is called a linear regulator and the other a switching regulator. Linear regulators for small DC voltages/current draws like detectors use look like small (roughly the size of your finger nail) flat transistor with a large metal heat sink on the head. This heat sink some times has a hole drilled into it so you can bolt a larger heat sink to that to bleed off the heat better. The reason why it needs the heat sink is because linear regulators can only take the excess voltage being fed into it and convert it into heat in order to drop the voltage output to the desired constant level. For that reason they are not very efficient at all, but they are very cheap and also less prone to generating electrical noise, unlike switching regulators.

The reason why a voltage regulator is required in some electronics isn't really because of longer battery run times (by having a larger voltage source than needed and thus a wider window of operation during drain down)...That's really a side benefit to things. The main reason why voltage regulators are needed in certain devices like metal detectors is because the circuit needs a stable/constant/non-changing source voltage in order to maintain best performance. If the voltage was constantly changing it would make the detector much more eratic as the source drained. With a regulator as the source (battery) drains the detector never sees that. If it wants say 9V to operate it's constantly being fed 9V even though the battery is draining from say 12.5V down to say 11.8V over a few hours time.

Switching regulators are much more efficient in that they don't waste that extra voltage by converting it into heat. Rather they control the output voltage by something called Pulse Width Modulation. This might not be the right name for it in voltage regulators but the concept is the same. Think of a light dimmer on your wall. As you turn the dial down the lights go dim, and vise versa. What happens is this...The circuit inside the dimmer sends out pulses of voltage so many times a second. As you dim the lights the number of pulses per second slows down, and as you raise the dimmer the number of pulses per second increases. Instead of the light seeing a constant voltage, it's being sent a pulsating voltage based on the level of power (brightness) you are sending to the light. ESCs (Electronic Speed Controls) in RC planes work the same way. As you increase throttle the PWM is increased to the motor. The motor or light never knows what's going on. It only seems the total or sum of power being presented to it by the pulses. Increase the rate of pulses and the total sum voltage to the device increases in a sense.

If switching regulators are so much more efficient in that they don't waste the extra voltage by turning it into heat, then why not use them in all devices? Mainly because they generate a lot of circuit noise with the pulsing output. They are not only more expensive but require the addition of more components on the board to help cancel out the noise being generated.

Now, I haven't looked close enough at my GT's circuit board to see exactly what it's using to control the voltage ouput. I would assume it's using a linear regulator. The other thing about these is that they can't output more voltage then they take in, and the input voltage usually has to be above the output voltage by say a volt and a half or two. In other words, if the GT wants a 9V output then the input voltage from the battery needs to be 10.5V or higher.

I've used linear regulators in projects here and there. For instance, in my aerial photography RC plane I'm using a pocket cam corder that runs on two AA 1.5V batteries in series. To eliminate that extra weight I plug the cam corder into a 3V regulator which has an input voltage of I think up to about 14V or so. The plane lipo's 12.6V is converted by the regulator down to a 3V output to power the camera, and the plane battery also powers the motor (via PWM using an ESC), the RX, and the servos. The ESC also has something on it called a BEC (battery elimination circuit) which is just a fancy name for voltage regulator. This BEC takes the lipo's 12.6V and outputs it as 5V to the RX and servos because that's what they need to run on. The regulator I'm using for the camera gets VERY hot if it's sitting on the ground with no air flow over it even though I bolted a large aluminum heat sink to it. For that reason I have this heat sink mounted to a cowl on the plane that will keep it cool with air flow while in flight. If I have it on for too long sitting on the ground the linear regulator will shut down on what's called a thermal overload. When that happens if you're lucky it will work again after it's cooled down.

Mainly the above point is this...I've heard of people in detecting land talking about using an extra cell or two to increase the power of their detector. It's not going to happen, and it's going to make the regulator very hot and you risk destroying it.