Battery/Regulator query

[Unregistered]

Hello Forum,

A posting on another forum from a experienced person with many years of detecting mentioned and I quote : "It is my understanding that a battery does not supply a smooth supply of power. As the battery releases the energy direct to the consuming circut there are small spikes and dips in the actual current. If you were to make this visual on a screen you could easily see what I mean. If the current is passing through a regulator the reg may only take out the higher spikes. After all, its primary function is to protect the circut from overload. Take the same decaying battery current and pass it through a regulator designed to smooth out those spikes and you get a better supply of power to your detector circut. This can result in a much smoother threshold and sharper signal"

I hope he does not mind me posting his understanding on this forum as I have wondered ever since reading the above and if indeed a Battery does spike and dip in its release of power intead of a smooth supply, and can a certain regulator provide a fix for a smooth threshold and sharper signal?

Thanks for your help.
Regards,
Brian

[Brian]

Sorry, I forgot to register for this forum, so have now done so as "Brian"

Cheers.

[Mike]

Welcome Brian,

If a battery is under a *steady* load, it is my understanding that the battery does not spontaneously produce spikes and dips. However, because of the battery's internal resistance, spikes and dips in the current consumption of the detectors electronics (for example, producing a sound when a taget is detected) can cause spikes and dips in the battery's voltage. The regulator will ensure that the voltage fed to the electronics remains constant, as long as the battery voltage remains above the regulators output voltage. This should give a smooth threshold and sharper signal.

If there was no regulator, the sudden tone produced as the threshold control crossed the threshold limit could cause jittery threshold adjustment. But this is due to the sudden current increase due to the threshold tone, which causes the battery volts to drop, not the battery being a generator of spikes and dips which are detected near the threshold. Without regulation you get unwanted, mostly negative, feedback effects.

As the battery volts drop over time with use, the regulated output from the regulator will stay constant up to a point. The regulation will stop when the battery voltage nears the regulators output voltage. At this point, the detector will continue to operate, but the voltage will be unregulated, leading to unstable and underperforming operation, for the reasons described above.

Hope this helps,

Mike

[J_Player]

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[J_Player]

Here is a graph of a 4.8 volt NiMH battery discharge voltage showing the spikes and dips. The dips can be much worse in an alkaline battery, whose voltage will fall off at a greater rate.

Take note this NiMH battery begins with a full charge of 5.5 volts then quickly drops to a range that holds between 4.8 and 4.5 volts. after that it finally decays as the charge is depleted. When this battery drops to 4.0 volts (or 1.0 volts per cell), the battery is done and needs to be recharged or you run the risk of causing one or more cells can reach a reverse polarity condition. This may help show the usefulness of a regulator.

[Largesarge]

A good filter between battery and regulator should keep your regulator output nice and smooth.

[Brian]

Thanks for yours replies,

The lithium-ion battery seems to be popular as a preferred battery in recent times, and I assume they have the best discharge curve with a longer flat line of constant voltage over all others types and maybe with less spikes.

I currently use a sealed lead acid 6v12Ah battery as my preferred supply and my friend uses a 7.2v7.8Ah lithium-ion battery via a 6v regulator into our identical PI model detectors which are 6v machines using an internal regulated 5v supply.

Now does his li-ion system produced a smoother threshold and sharper signal response than my SLA system I cannot say for sure except, I suppose the internal regulator in the detectors places us both back on a equal terms?

Regards,
Brian

[Mike]

Hmmmmm......

Brian,

Just for information, the discharge curve in J Players post above looks like it's the second image at http://shdesigns.org/batts/battcyc.html To quote from that web page, "The small spikes in the plot are due to noise in my meter circuit (design is a prototype.)". So the spikes and dips (i.e. noise) on this curve are not generated by the battery.

I'm no electrochemistry expert, but it is still my understanding that batteries do not produce spikes and dips which are not due to load fluctuations. So lithium-ion batteries, lead acid or any other technology don't produce noise and so are not different in this respect.

Changing the subject slightly, what detectors are you using? If the internal regulator output is 5V, and the recommended battery voltage is 6V, you don't have much headroom before you have to recharge the battery. Now you obviously have to take with a pinch of salt any advice offered by some guy you've never met on a forum, which includes me. But you and your friends detector might be able to operate directly from his 7.2V battery pack without the 6V regulator, so getting a longer run time before recharging. But please don't try this without checking the handbook and/or manufacturer first, though. Just a thought.

Regards,

Mike

[J_Player]

1. You are right about the curve. That battery was not connected to a constant load. In the graphic, the load was removed for 1 second before taking each measurement along the curve. Whether the meter caused the noise as stated, or it was the battery voltage recovering from the load, I am not sure.

A battery connected to a fixed resistive load with a voltmeter attacheded does not show any significant dips or spikes. The circuitry connected to the battery causes these dips and spikes. When charting the voltage of a battery "in use" on a metal detector, the spikes look sharp like noise when they are compressed into a chart of the full discharge time of the battery. If you were to look at a magnified portion of the voltage curve covering a 5 second period, you would find that the dips and spikes are more rounded and look less like noise than when shown on the full discharge time chart. The point is that internal resistance of the battery will determine the degree of dips and spikes caused by changes in the current drawn. Sorry if I caused any confusion.


2. The headroom for NiMH and Li-ion works out very well because they have a pretty flat discharge curve. If a 6V NiMH battery drops to 5V, then the battery is at a point where almost all the usable charge is used up, and the battery needs to be recharged in order to avoid the risk of cell reversal. The same is true of Lithium ion batteries, except the voltages are very slightly different. Alkaline batteries have more of a slope to their discharge curve, so the headroom issue is a real problem.

Here is a link to some detailed tech manuals from a manufacturer of rechargable batteries. They show the graphs of discharge rates which should explain why the headroom issue is not a problem NiMH or Li-ion type batteries (this is not true of some other type batteries). You will also find a lot of information about charging these batteries, and the some facts that are contrary to popular myths about the rechargables. http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf http://www.sanyo.com/batteries/pdfs/lionT_E.pdf

[MojaveRed]

Brian and Others,

This is an interesting thread. I've considered regulators placed over the whole battery pack as mentioned by by Brian, but always wondered about the following:

Consider Carl's Hammerhead design which is probably representative for this discussion. In the HH, the whole battery is across (i.e., placed in parallel with) the coil. Thus the internal electronics of the regulator (capacitances (?), etc) are in parallel with the coil.

This line of thinking leads one to suspect that a regulator on the battery could possibly be detremental to performance, particularly if the coil sees capacitance in the regulator.

Another question I have is, What is the response (or effect of the response) of the regulator to the flyback voltage, which the regulator surely has imposed across its terminals?

Since Brian and his friend have the same PI detector, except that one has a regulator on its battery, it would be of interest to know whether any quantifiable difference in performance can be seen between the two detectors.

[J_Player]

Hey MojaveRed, I would suspect you're right about a regulator on the battery could possibly be detremental to performance of a Hammerhead. In the Hammerhead design, It looks like Carl designed around the problem of noise from the coil by clocking the 7660 regulator with the same clock that fires the coil. It seems like the idea was to allow any coil pulse noise to happen synchronous with the regulator clock. I would think C1 also has some filtering effect on the battery. It would be interesting to hear from Carl about this. I suspect most metal detector manufacturers also incorporate methods in their circuitry to minimize this kind of noise problem.

Back to what battery:
If there was ever a problem caused by excessive internal battery resistance, a person could switch to a battery with less resistance. Of the common types of rechargables, the NiCad has the lowest internal resistance. These are still used in RC race cars where very high current draw is needed. They are noted for losing their charge when stored for a few weeks.

NiMH has internal resistance higher than a NiCad, but still low. They are popular because they can deliver up to twice the power of a NiCad, and have less memory effect. These batteries also lose their charge when stored for a few weeks.

The Li-ion batteries have about twice the capacity of NiMH the same size and voltage, and they don't loose their charge after sitting a few weeks like a NiMH and NiCads. But Li-ions are not generally used for high current applications. These are popular in cell phones where size and weight are critical. Whether these Li-ion batteries are suitable in a metal detector probably depends on whether the current draw is within the safety limits for the size Li-ion battery being used. The battery manufacturers caution that if a Li-ion battery is subjected to too large a current draw (or too much charging current), the internal resistance could cause the battery to overheat and start a fire or explode, even though they have built-in pressure vents for safety. Apparently this has been a concern with Li-ion.

If I had to decide, I would probably choose NiMH, and live with the need to charge the battery a day or two before using the detector. There are also safe 1-hour chargers for NiMH batteries that can run from your car cigarette lighter or from an inverter in your car.

[Cossaro]

My new battery system...

In my test over the discharge of a battery pack i found the same problem, the voltage is not constant but the "spikes" are not really dangerous, they are like a very low frequency noise (form 1 to 3 Hz ).

When you compress it in a graph, for better display the dischg. decay, those variations appear like spikes (the view-problem is only the scale factor).

take a look here...
http://www.forumfree.net/?t=7056781

this is my (new) custom regulator that stabilize the power in a sover-elite and try to make a test with a little over-voltage.

The main reason because no regulators are used in portable MD is trivial... the drop-out voltage over the regulator is a cost for the device and reduce the normal usage by 10-12% in the total time.

by

[J_Player]

It looks like you are running Lithium ion batteries cossaro. How much extra detector time did you gain after making the modifications?

[Brian]

Many thanks again to all for your feedback.

Mike, Our detectors are both Minelab PI’s (GP3000) and I am not certain of exact voltage output of its internal regulator but I think it is around 5.5 volt mark to run its circuit, and I believe the detectors flat battery alarm sounds off at 5.6volts. My friend’s 7.2-volt 7800mAh Li-ion system charges up to around 8.2 to 8.4 volts and releases this voltage into the detector via its external regulator set to 6.7volts, which should last around 7.5 to 8.5 hours of use.

Some feedback I have read on another forums says some 3000’s can run at 7.2 volts and others will shut down. The external regulator can also be switched to 7.2 volts for use on earlier model Minelab PIs giving them some performance gain. However our later model machines use dual voltage technology internally for its performance gain. My SLA battery charges up to 6.55 volts and today I detected for around 7 hours with Mono and DD coils as well as running an audio booster, an external speaker system instead of headphones and after 7 hours my SLA had dropped to 6.23 volts.

The only advantage I see with the Li-ion system is the large reduction in weight to lug around compared to the gel cell SLA. Although I am not sure of the difference in internal resistance between the two types to cope best with any dips and spikes caused by changes in current drawn as J Player mentioned.


Brian.

[J_Player]

Hi Brian,
The reason I shy away from the Li-ion batteries is not because I because of noise problems due to internal resistance. It is because they are more
susceptible to environmental elements and require more careful treatment than the NiMH batteries. Did you ever wonder why the laptop Li-ion
batteries are only good for a couple of years? Here is an overview of a number of things I haven't mentioned about Li-ion batteries:

1. Li-ion batteries have internal resistance a little higher than nickel base batteries. But as a Li-ion battery goes through it's discharge cycle,
this internal resistance increases noticably. This amount is still not of major concern for a metal detector. However, a few months after the new
battery goes through it's charge cycles, the internal resistance becomes greater and continues to rise, causing a reduced current capacity of the
battery. Eventually the current capacity decays to where it is a problem for a metal detector. This increased internal resistance will happen with
age whether the battery is being used or not.

2. Li-ion batteries will become useless in 2-3 years whether you use them or not. They will stop delivering a usable current because the internal
resistance has risen so high as to limit the current to a small amount.

3. Temperature helps to cause a Li-ion battery to die sooner. The worst working environment for Li-ion batteries is to be fully charged and kept
warm. This often occurs when you begin a hunt and your detector is in the sun, so the temperature inside the case where the batteries is even
warmer. A way to extend the life af Li-ion batteries is to store them in a cool surounding with 40% charge.

4. Li-ion batteries need a special charger that works much different than nickel or lead batteries. As long as you use the special Li-ion charger
you will have no problem. But if you over charge the battery or run it down completely, then you can expect damage to the battery capacity that is
not reversible. If you have a cell reversal, also expect some irreversible damage. Maximum battery life comes when you recharge a Li-ion battery
after shallow discharges. The deep discharges shorten the life.

5. There is an overheating problem if the battery is shorted, connected to a load higher than the recommended safe limit, or if it is charged at too
high a rate. The battery overheats because of the internal resistance cause it to operate as a heater during high current flow. Simple overheating
will cause a permanent loss of capacity. These batteries will also overheat or possibly explode if they are dented bad enough to cause an internal
short across the pole separator. Safety devices like thermal circuit interrupters and pressure vents are installed on Li-ion battery packs to
prevent serious injury in case of this kind of accident. Most often, Li-ion applications are arranged so the battery is not normally removed by the
consumer for charging. Charging is done by connecting the charger to the appliance that houses the battery (cell phones, laptops). I suspect this is
a safety design to prevent users from accidentally shorting the battery or physically damaging it to cause it to explode or start a fire. Li-ion
batteries have a 20 year history of development. It has only been in the past few years they were made safe enough for use in large scale consumer
markets.

6. On the plus side for Li-ion, they weigh about a quarter that the same power NiMH battery weighs. Also, they only lose 5% of their charge after a
month of storage compared to 30% for a NiMH, and have no memory effect.

When I look at the temperamental nature of a Li-ion battery, I figure I would just as soon use NiMH types. Not that the extra weight savings and
ability to keep its charge for weeks isn't tempting. My feeling is Li-ion batteries have not reached as mature a stage of development as the NiMH
batteries have.


There is some good technical information about these two types of batteries in the links I posted. Here they are again:
http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf
http://www.sanyo.com/batteries/pdfs/lionT_E.pdf