Amperage fluctuations

Something that has been bugging me for the last runs I did : I use a Powerpak 300 from BioRad in clamped voltage mode. However, the current intensity fluctuates quickly (at 30V, from 0.7A to 1.2A). This is a problem because if the current changes too quickly, the power generator shuts down thinking the circuit is shorted (I have the error message : "change in resistance detected"). If it happens during the night, the system is then not running for a long time, because it has to be manually reset.

Does anyone have the same problem, or is there something wrong with my setup?


  • AReadyAReady Posts: 7
    I've had similar problems from time to time. Honestly I just have to turn the alarm off through the Setup menu on the Powerpak and hope for the best.
  • joelrosienejoelrosiene Posts: 63
    edited June 2013
    Same issue here - my assumption is that the amperage fluctuations correlate to fluctuations in resistance based on changes in fluid volume within the chamber as well as movement of the sample. If you stop the program on your BioRad, click the button down to the "Current" setting, and hold the stop button for 4 seconds, it will read dE09, which will prevent the power supply from shutting down when it detects the change in resistance.

    Edit: Nicolas what temperature do you run at? My experience is that temperature of the solution influences the specific resistivity of the solution to a great degree. Running a chamber (not to Stanford spec) at 37 vs 50 C has produced an exceedingly wide range of amperage. (increasing temp from 37 to 50 results in a 4x increase of amperage). I will post my calculations.
  • I ran my first sample at 20V and 37C for five days--- the current also fluctuated between ~700-850 mAmps but did not shut off the BioRad power supply. When I put a second sample in, I tried to increase the voltage and my current was stable around 800mAmps and then plummeted, shutting the system down. Instead of overriding the shutdown, I would prefer to understand why the chamber suddenly has such a crazy resistance. Instead of providing a voltage range, I wish the protocol had referenced the current they were using initially for their tissue. This is just one of the problems I am having with the setup.
  • kadi

    I do have a previous post which is somewhat relevant to this issue, if you are interested;
  • FabioFabio Posts: 62
    Im running now 20 V at 37°C. After 5 days of clearing my amperage fluctuates between 0.8 A and 0.81 A.

    I have also noticed that at that temperature and working under a hood my buffer volume decreases (evaporation). This leads to increased concentrations of ions and SDS. Higher ionic concentration affects amperage.

    What I do is to have a fill mark and refill constantly with H20 my circulator. (If you fill in Clearing solution you will further increase ion concentration).

    This way my amperage remains constant
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