Periodic voltage noise when using 12V batteries as power supply

[Reinhard]

Dear All,

We are trying to use two 12V batteries instead of DC power to reduce the system noise level. The results did have smaller noise but we found these periodic (every 2 to 3 seconds) large voltage pulses (in range of +/- 3mV), which were not shown when the batteries were off. Did anybody observe similar phenomena? Actually, we found that the LM317 and LM337 voltage regulators were very hot during the measurement, and we don't have heat sink for them currently. Is it necessary to have heat sinks? Could it be the reason of the large voltage pulses?

Thank you all in advance.

[Jon Newman]

Hi,

I don't remember what the current drawn by the amplifier is, but if you are providing your linear regulators with +/- 12V from the batteries then that will create about 6 V drop across the regulator to get the votlage down to the +/-5 volts required by the amplifier. If the amplifier board is drawing 100 mV (which does seem a bit high, but i cant remember what the current draw is) then thats ~0.5 watts disspilated by he regulator which would make it hot under normal circumstances.

That said, have you probed the power line the amplifier without it being plugged in? If you see this artifact on the power lines to the amplifier then you know something is wrong with the battery --> linear regulator circuit.

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[Reinhard]

Hi Jon,

Thank you for the advice. We monitored the power line without connecting the amplifier and found it to be +/-6V exactly. So the regulators should be working fine. At the meantime, we checked the temperature of the regulators with the amplifier connected and it increased very fast. The abnormal large voltage noise was not observed this time as we stopped it when the regulators temperature reached 90c. Therefore, we guess that the high temperature of the regulators may cause the noise. Thus, we are purchasing some heat sinks or small fans. If you have any suggestions, please let us know.

Thank you again.

On Thursday, October 29, 2015 at 9:56:23 PM UTC+8, Jon Newman wrote:

Hi,

I don't remember what the current drawn by the amplifier is, but if you are providing your linear regulators with +/- 12V from the batteries then that will create about 6 V drop across the regulator to get the votlage down to the +/-5 volts required by the amplifier. If the amplifier board is drawing 100 mV (which does seem a bit high, but i cant remember what the current draw is) then thats ~0.5 watts disspilated by he regulator which would make it hot under normal circumstances.

That said, have you probed the power line the amplifier without it being plugged in? If you see this artifact on the power lines to the amplifier then you know something is wrong with the battery --> linear regulator circuit.

On Thu, Oct 29, 2015 at 5:57 AM, Reinhard <laos...@gmail.com> wrote:

Dear All,

We are trying to use two 12V batteries instead of DC power to reduce the system noise level. The results did have smaller noise but we found these periodic (every 2 to 3 seconds) large voltage pulses (in range of +/- 3mV), which were not shown when the batteries were off. Did anybody observe similar phenomena? Actually, we found that the LM317 and LM337 voltage regulators were very hot during the measurement, and we don't have heat sink for them currently. Is it necessary to have heat sinks? Could it be the reason of the large voltage pulses?

Thank you all in advance.

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[Jon Newman]

OK, good. A few more things:

- Did you monitor the regulator output with a mulitmeter or a real scope -- the multimeter will tell you nothing about transient signals on your power lines.

- Put your meter in current test mode, and put it in series with the power output from the regulators. How much current is being drawn? It sounds like something might be wrong with your amplifier if your a drawing enough current to make the regulators this hot.

- Linear regulators get hot under normal operation and most are specified to reach upwards of 100 deg. C under normal operation. I agree that if they are reading 90 deg. that quickly, they probably need a heatsink. However, I'm very suprised they are getting that hot in the first place and I don't understand what is drawing so much current. 

On Thu, Oct 29, 2015 at 11:34 PM, Reinhard <laos...@gmail.com> wrote:

Hi Jon,

Thank you for the advice. We monitored the power line without connecting the amplifier and found it to be +/-6V exactly. So the regulators should be working fine. At the meantime, we checked the temperature of the regulators with the amplifier connected and it increased very fast. The abnormal large voltage noise was not observed this time as we stopped it when the regulators temperature reached 90c. Therefore, we guess that the high temperature of the regulators may cause the noise. Thus, we are purchasing some heat sinks or small fans. If you have any suggestions, please let us know.

Thank you again.

On Thursday, October 29, 2015 at 9:56:23 PM UTC+8, Jon Newman wrote:

Hi,

I don't remember what the current drawn by the amplifier is, but if you are providing your linear regulators with +/- 12V from the batteries then that will create about 6 V drop across the regulator to get the votlage down to the +/-5 volts required by the amplifier. If the amplifier board is drawing 100 mV (which does seem a bit high, but i cant remember what the current draw is) then thats ~0.5 watts disspilated by he regulator which would make it hot under normal circumstances.

That said, have you probed the power line the amplifier without it being plugged in? If you see this artifact on the power lines to the amplifier then you know something is wrong with the battery --> linear regulator circuit.

On Thu, Oct 29, 2015 at 5:57 AM, Reinhard <laos...@gmail.com> wrote:

Dear All,

We are trying to use two 12V batteries instead of DC power to reduce the system noise level. The results did have smaller noise but we found these periodic (every 2 to 3 seconds) large voltage pulses (in range of +/- 3mV), which were not shown when the batteries were off. Did anybody observe similar phenomena? Actually, we found that the LM317 and LM337 voltage regulators were very hot during the measurement, and we don't have heat sink for them currently. Is it necessary to have heat sinks? Could it be the reason of the large voltage pulses?

Thank you all in advance.

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http://www.mit.edu/~jpnewman/

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[Reinhard]

Hi Jon,

We monitored the output using a real scope. It showed +/-6V. As you suggested, we measured the current but by using a multimeter. The current was around 0.6A when the batteries were connected, which was same as when the DC power supply was used. Is this 0.6A reasonable? Is it too large? If it is too large, does it mean that something was wrong with the pre amplifier?

We tried to supply a sine wave signal to the commercial MEA (60StimMEA200/30-Ti). We filled the culture chamber with 1x PBS solution and one end of the sine wave signal was directly inserted into the solution, the other was connected to the ground of the pre amplifier. We tried 100 mVpp with frequency of 20Hz but no signal was displayed in NR. Does this indicate that the MEA chip was not working?

Thank you very much.

On Friday, October 30, 2015 at 10:06:08 PM UTC+8, Jon Newman wrote:

OK, good. A few more things:

- Did you monitor the regulator output with a mulitmeter or a real scope -- the multimeter will tell you nothing about transient signals on your power lines.

- Put your meter in current test mode, and put it in series with the power output from the regulators. How much current is being drawn? It sounds like something might be wrong with your amplifier if your a drawing enough current to make the regulators this hot.

- Linear regulators get hot under normal operation and most are specified to reach upwards of 100 deg. C under normal operation. I agree that if they are reading 90 deg. that quickly, they probably need a heatsink. However, I'm very suprised they are getting that hot in the first place and I don't understand what is drawing so much current. 

On Thu, Oct 29, 2015 at 11:34 PM, Reinhard <laos...@gmail.com> wrote:

Hi Jon,

Thank you for the advice. We monitored the power line without connecting the amplifier and found it to be +/-6V exactly. So the regulators should be working fine. At the meantime, we checked the temperature of the regulators with the amplifier connected and it increased very fast. The abnormal large voltage noise was not observed this time as we stopped it when the regulators temperature reached 90c. Therefore, we guess that the high temperature of the regulators may cause the noise. Thus, we are purchasing some heat sinks or small fans. If you have any suggestions, please let us know.

Thank you again.

On Thursday, October 29, 2015 at 9:56:23 PM UTC+8, Jon Newman wrote:

Hi,

I don't remember what the current drawn by the amplifier is, but if you are providing your linear regulators with +/- 12V from the batteries then that will create about 6 V drop across the regulator to get the votlage down to the +/-5 volts required by the amplifier. If the amplifier board is drawing 100 mV (which does seem a bit high, but i cant remember what the current draw is) then thats ~0.5 watts disspilated by he regulator which would make it hot under normal circumstances.

That said, have you probed the power line the amplifier without it being plugged in? If you see this artifact on the power lines to the amplifier then you know something is wrong with the battery --> linear regulator circuit.

On Thu, Oct 29, 2015 at 5:57 AM, Reinhard <laos...@gmail.com> wrote:

Dear All,

We are trying to use two 12V batteries instead of DC power to reduce the system noise level. The results did have smaller noise but we found these periodic (every 2 to 3 seconds) large voltage pulses (in range of +/- 3mV), which were not shown when the batteries were off. Did anybody observe similar phenomena? Actually, we found that the LM317 and LM337 voltage regulators were very hot during the measurement, and we don't have heat sink for them currently. Is it necessary to have heat sinks? Could it be the reason of the large voltage pulses?

Thank you all in advance.

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http://www.mit.edu/~jpnewman/

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[Jon Newman]

I don't have access to an amplifier in my current lab. Does anyone know how much current these things draw nominally?

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[Riley Zeller-Townson]

Sorry I'm late to the party- 

The MCS manual on the 1060 has the supply current listed as +/- 350 mA

http://www.multichannelsystems.com/sites/multichannelsystems.com/files/documents/manuals/MEA1060-Inv-BC_Manual.pdf , see section 7.1.2

One of our NR rigs, which is powered via a DC power supply, draws 115 mA on each terminal (so, total of 230mA) when the amplifier is plugged in to the MCS cable but without an MEA placed inside, and  150 mA on each terminal (so 300 mA total) when a test MEA is place in the amplifier (and properly grounded).  With the amplifier unplugged, those same terminals draw about 10 mA each.  All of those numbers came from the report off of the power supply itself.  Note that the voltage regulators are bypassed on this rig. (See instructions here: https://sites.google.com/site/neurorighter/user-manual/system-setup#_Toc226960246 )

So, the 600 mA you are drawing does sound a high, however even if you got it down to the 350 mA suggested, you'd still be looking at 1.7 W of heat generation.  A heat sink would be a good idea.

When you tested the current draw using the DC supply, were the voltage regulators on the NR board bypassed or were they used?   I don't think that should affect the current draw tremendously, but it would be worth a quick check. 

as for your 20 hz test, make sure you do that with the 'spike filter' unchecked (as it should filter out signals in that band).

Riley Zeller-Townson

PhD student, Potter lab

Laboratory for Neuroengineering

Georgia Tech/Emory University

Atlanta, GA, USA

[Reinhard]

Hi, Riley

Sorry for the late reply. Actually we have a set of amps to achieve 1100 gain, which contains a preamp and a filter amp as the manual you cited. In the page 49 and 50 of the manual, they mentioned the current of preamp is +/-350 mA and the current of filter amp (FA60S-BC) is +/-200 mA. Does that mean the total current should be around +/-550mA? How many amps do you use in your setup? If you are using only one, what's the gain and current of that?

When we tested the current draw using DC power, the voltage regulators were bypassed. 

 

For our 20 hz test, we did unchecked the spike filter. But still nothing could be seen.

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[Riley Zeller-Townson]

Reinhard

my goof- I referenced the wrong manual!  We use the upright preamplifier here: http://www.multichannelsystems.com/sites/multichannelsystems.com/files/documents/manuals/MEA1060-Up_Manual.pdf

From what I can tell, this amplifier includes the 'filter amplification' stage in the same piece of hardware as the 'preamplifier'.  So no, we don't have an additional amplifier beyond that one.

Fortunately, it seems that the current draws you are reporting line up nicely with the specifications for *your* amplifier system (the combined 1060-Inv-bc and FA60s-bc)- so, that's good.  

Has anyone on the list successfully used a FA60s-bc with neurorighter before?

I don't have experience using the two-stage amplification system myself.  I do know of a non-functional rig that has this, but in that rig's case the power is supplied through the MC_card itself, which in turn is powered through the MCS internal power supply (http://www.multichannelsystems.com/sites/multichannelsystems.com/files/documents/data_sheets/IPS10W.pdf)  

I might suggest using the DC power supply to increase the supplied voltage *slightly* above 6v+/-.  You could go up to 6.3 to match the voltage being supplied to the MC_card, or 6.5 to be within the spec of the datasheet.  While the 1060-UP preamps work fine at +/- 6v, it is possible that the second stage requires a slightly higher voltage.  Please do this at your own risk though, as, I don't have any experience with that system directly!

good luck

-Riley

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Riley Zeller-Townson

PhD student, Potter lab

Laboratory for Neuroengineering

Georgia Tech/Emory University

Atlanta, GA, USA

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