PI Voltage ??

[revmaster]

Hi,
I am using 12v battery for my PI, if i reduce supply voltage to 8v and keeping pulse width & freq same then will the sensitivity reduce ? or am i wasting my energy by pumping in more power @12V.
Am asking this because -ve kick expereinced by coil is of the same level in both the cases, hence sensitivity should not reduce.

Regards,
Michael

[Reg]

Hi Michael,

If you reduce the voltage to 8 volts, you will have a slight reduction in sensitivity, but most likely will not be able to easily notice it.

As for the "kick" voltage being the same, remember the FET's have a zener across them to limit the maximum voltage across the FET. This zener voltage will try to limit the "kick" to the FET zener voltage level, so you will not see any or little difference when looking at the "kick".

If you decide to try to use a voltage of 8 volts instead of 12 volts on a PI design such as the Hammerhead, you may run into trouble in generating a steady solid +5V if the +5 voltage is developed using some form of voltage doubler.

Reg

[gef12]

pi voltage

Hi
On the same token I think puting an adjustable volt regulator after the 12 volt battery and set that to about 10.5volts that would be ok to run the pi thence the 7660 would be happy .. think this is same principle as chemelecs unit is ???
thanks reg

gef

[Charles (Upstate NY)]

Doesn't current play a role in sensitivity? I'm curious which is more of a factor voltage or current. 6 volt high current versus 36 volt low current. Seems like I read recently the Nautalis croud bragging about being able to zap the ground with up to 40+ volts via 4-9 volt batteries.

[robert]

What about current?

Voltage....? What about current?

[Carl-NC]

What matters is the strength of the "ON" magnetic field (B), and how fast you can turn it off (dt). That is, you want a large dB/dt to get maximum induced target eddy currents. The ON magnetic field depends on current (not voltage) and coil inductance. Practical inductance is limited by settling requirements, so the ON current and the switch-off speed are left. The flyback voltage is merely a result of L*dI/dt and not all that important in itself. As Reg said, it can be limited by the breakdown voltage of the transistor.

So, for PI a 6V high current battery would be better than a 12V low current battery.

Nautilus is VLF, not PI, but for depth you again want high currents through high inductance coils for maximum target "inductivity". Since the is no abrupt turn-off to assist with the dB/dt, you have to drive the coil with a high AC voltage to get the dB/dt.

- Carl

[Alexismex]

Hello forum , I agree for the current but the voltage is also important .For me there is a BIG difference (in field test better) if you work with 12V (with nicad o nimh ) again a 10,5V ...before I use 12V gelcel and 10,5V after regulation,
now I use a low drop regul 12v like the 2990 with thisconfiguration i can use gelcel (but at X20 the decharge for exemple if your circuit need 200mA a battery of 4Amps minimum is needed) , or use nicad or nimh (for the nimh there are not heavy , no memory etc...etc... But for me 1 year of use and you must replace, the nicad are MORE durable 4-5 o more years....I made many experiments to increase voltage from 9V to 20 V checking also the current and definitivly you have a big difference in sensibility and "more punch " in the receive signal with 12V...
best regards a tous.

[Reg]

Hi All,

If you reduce the voltage from 12V to 8 V and you are working on the linear portion of the current curve, you will have about 2/3 current at the 8V at time of shutoff. This 2/3 value occurs with a very low resistance coil and associated circuitry or with a very high resistance after the current is at maximum.

I have not found that dramatic of a depth difference when changing the current that much. What can happen is the extra voltage can cause one to sample closer to the critical point on the signal rise to 0V. If that happens then there can be a significant sensitivity increase.

To assure that isn't happening, simply turn the delay back far enough that increasing the voltage doesn't come close to moving the sampling time closer to the critical point.

Reg

[Carl-NC]

I should have better explained that low voltage is fine if you design for the low voltage. If you take a circuit that was designed for 12V and reduce the battery to 6V, then the resulting coil ON current will decrease because the coil R and switch R did not change. But if you design for 6V, then you can get results just as good for equal dB/dt.

- Carl

[Geo]

As Carl said for any voltage you must redesigne the circuit. If so then there is not big change. I tried these changes (9...24V) and i saw that with the right coil the performance was the same (or about the same). For me low voltage is better (9v is ok) because we have faster pulses (time to rise).

[revmaster]

DC resistance of my coil is 1.3ohm and pulse width is about 100us, reducing voltage from 12v to 9v i didnot see any difference in sensitivity.
Carl - what changes do i need to do to operate it on 6v, my design is similar to HH but with some modifications.
Can i use a dc/dc converter but will it provide surge current when needed by pulse ?

[1843]

I think that by increasing the power supply two times, the PI power will increase four times!
Pay attention to this formula:
P=V.V/R

Regards

[revmaster]

I think that by increasing the power supply two times, the PI power will increase four times!
Pay attention to this formula:
P=V.V/R

Regards

I dont think for PI this formula is applicable, but should be a function of induced eddy currents. Perhaps there is a point of saturation where further increase will give very less or no benefit.

[Carl-NC]

I think that by increasing the power supply two times, the PI power will increase four times!
Pay attention to this formula:
P=V.V/R

This is for thermal power dissipated in a resistor. What we are interested in is the magnetic energy produced by the coil. This is uNI/2R at the coil center. So it is proportional to coil current.

Carl - what changes do i need to do to operate it on 6v, my design is similar to HH but with some modifications.
Can i use a dc/dc converter but will it provide surge current when needed by pulse ?

You need to consider battery discharge, so for 6V I would run the sub-supplies at +/- 3V instead of 5V. Given that, just tweak everything for the lower voltages. You will also want a MOSFET that has a low Ron with the lower gate drive and you might need to lower the coil R by using a heavier gauge wire.

You do not want to run the coil off of any kind of regulator or DC/DC converter unless it is specifically designed to meet your needs. Otherwise, you are sure to make things worse.

- Carl

[Charles (Upstate NY)]

Voltage....? What about current?

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