Results 1 to 8 of 8
  1. #1
    CAPTAIN FANTASTIC's Avatar
    CAPTAIN FANTASTIC is online now Registered User
    Location : Living in West Berkshire, sailing in the Solent
    Join Date
    Jul 2009
    Posts
    1,525

    Default Which digital Amp meter?

    I would like to install a small digital Amp meter like this one on ebay
    http://www.ebay.co.uk/itm/100V-500A-...item2a1d6f5f27

    There are various types; 10 amps, 50 amps and higher. Also some of them include a Shunt.

    My electrical system is made up of 5 x 110 amp batteries charged by a Rutland 913 windcharger and an engine driven alternator (60 or 80 amps I think); never had any problems. At present there is an old amp meter which I am not sure whether it works or not.

    So, which Digital meter do I need; do I also need to have a Shunt?

  2. #2
    Join Date
    Nov 2009
    Posts
    1,217

    Default

    Quote Originally Posted by CAPTAIN FANTASTIC View Post
    I would like to install a small digital Amp meter like this one on ebay
    http://www.ebay.co.uk/itm/100V-500A-...item2a1d6f5f27

    There are various types; 10 amps, 50 amps and higher. Also some of them include a Shunt.

    My electrical system is made up of 5 x 110 amp batteries charged by a Rutland 913 windcharger and an engine driven alternator (60 or 80 amps I think); never had any problems. At present there is an old amp meter which I am not sure whether it works or not.

    So, which Digital meter do I need; do I also need to have a Shunt?
    You do need a Dc-Dc converter module which is about a tenner - it fits in the power supply lines to the meter as shown in one of the connection diagrams.

    eg
    http://www.ebay.co.uk/itm/New-High-Q...-/300611704904

    You do also need a 75mv shunt - a 100amp one would do such as:
    http://www.ebay.co.uk/itm/100A-75mV-...-/150592185505

    Then connect it up as per the bottom right diagram.

  3. #3
    William_H is offline Registered User
    Location : West Australia
    Join Date
    Jul 2003
    Posts
    8,845

    Default Volt meter /amp meter

    This looks like a good unit and excellent price.
    However as said it needs a power supply module unless you run it on a 9v battery in which case a power switch and only turn it on when reading it. (70 ma is a fair bit of battery current) You can't run it off the 12v supply you are measuring as the negative of the supply for the meter is different voltage level to that you are measuring. hence the power module will produce a 5v DC that is isolated from ships battery but powered by it.
    The volt meter has 3 digits. hence described as 100 volts Actually 99.9 volts max. More common is described as 3.5 digits where there is the digit 1 at the begining so max is 19.99 volts giving you another decimal place of clarity (discrimination) but not necessarily accuracy. (more suitable for 12v system)
    A said the amp meter will need a shunt presumably supplied. This will drop 200mv (.2v) when the current is at maximum reading of the meter. A higher current range will give less discrimination (accuracy) but will when current is low in the range give less volt drop.
    You should consider looking at the existing amp meter especially if is nicely mounted in a panel. Analogue amp meters can be very adequate need no current supply and are usually accurate enough for what you want. A digital volt meter on the other hand is good but you cna find them that will measure the supply they are running off. No isolation needed. good luck olewill

  4. #4
    Join Date
    Nov 2009
    Posts
    1,217

    Default

    Quote Originally Posted by William_H View Post
    This looks like a good unit and excellent price.
    However as said it needs a power supply module unless you run it on a 9v battery in which case a power switch and only turn it on when reading it. (70 ma is a fair bit of battery current) You can't run it off the 12v supply you are measuring as the negative of the supply for the meter is different voltage level to that you are measuring. hence the power module will produce a 5v DC that is isolated from ships battery but powered by it.
    The volt meter has 3 digits. hence described as 100 volts Actually 99.9 volts max. More common is described as 3.5 digits where there is the digit 1 at the begining so max is 19.99 volts giving you another decimal place of clarity (discrimination) but not necessarily accuracy. (more suitable for 12v system)
    A said the amp meter will need a shunt presumably supplied. This will drop 200mv (.2v) when the current is at maximum reading of the meter. A higher current range will give less discrimination (accuracy) but will when current is low in the range give less volt drop.
    You should consider looking at the existing amp meter especially if is nicely mounted in a panel. Analogue amp meters can be very adequate need no current supply and are usually accurate enough for what you want. A digital volt meter on the other hand is good but you cna find them that will measure the supply they are running off. No isolation needed. good luck olewill
    No shunt is supplied and it needs a 75mv one according to the listing.

    But he could use any digital voltmeter most of which read 0-199.9mv and
    don't need an isolated supply.

    Using a 100mv/200a shunt, then the meter would read 0-199.9amps. (or 0-99.9 amps with a 100a shunt)

  5. #5
    Join Date
    Jul 2010
    Posts
    234

    Default

    Also is that able to show a - or + on the amp meter? I cant tell from the pictures.

  6. #6
    Join Date
    Jul 2001
    Posts
    671

    Default

    The original advertisement states that it needs a 500A/75mV shunt. If you use a 100A/75mV shunt then the calibration will be wrong and the meter will read 500A when the current is only 100A. All curent reading will be multiplied by 5. If you only need it to carry 100A then you could use a 100A/15mV shunt if you can find one.
    Dave Seager
    Weybridge UK

  7. #7
    Join Date
    Nov 2009
    Posts
    1,217

    Default

    Quote Originally Posted by Dave_Seager View Post
    The original advertisement states that it needs a 500A/75mV shunt. If you use a 100A/75mV shunt then the calibration will be wrong and the meter will read 500A when the current is only 100A. All curent reading will be multiplied by 5. If you only need it to carry 100A then you could use a 100A/15mV shunt if you can find one.
    Its easy enough to divide a 100a 75mv shunt's output down to 15mv with 2 resistors.

  8. #8
    Join Date
    Nov 2009
    Posts
    1,217

    Default

    Quote Originally Posted by the_branflake View Post
    Also is that able to show a - or + on the amp meter? I cant tell from the pictures.
    It doesn't look as though it can display minus amps and the blurb only states 0-500a and there doesn't seem to be space for a - sign.

    Simplest option is to buy a couple of standard 199.9mv digital voltmeters, a 100a/100mv shunt and use one for amps and one volts.

    The ammeter will read + and - amps and a cocuple of resistors will enable the other to read upto 19.99volts.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •