Ammeter shunt -- protection enclosure (isolation)

[billythefish]

Hi, I was wondering if anyone had fitted an enclosure around their ammeter shunt, given that, as supplied, there's a fair amount of current which can be readily touched and thus it provides a danger in most firewall-forward installations.

Ideally I'm looking for a supplier that provides ready-made enclosures (or boxes) which I can fit around my shunt so that it does not provide a risk of a short / spark / other electrical anomaly!

By my reckoning (I'm European / metric ) the size is 150mm x 50mm x 30mm.

cheers,
=bill

 

[dynonsupport]

Bill,
We do not have a recommendation ourselves on a cover. Perhaps another customer has a suggestion.

The shunt is usually connected near the alternator, ahead of the load, so it will be at system voltage level (12V or 24V nominally.) The current through it is not a concern in itself, but it is at the high voltage level so should be treated like the positive side of the battery or alternator.

-Dynon Support

 

[RV711AC]

I mounted my shunt with a pair of 10-32 M-F standoff's with the intent of adding a thermoformed plexiglass cover. I have not made the cover. The cover could be aluminum but there is some concern about the terminals loosening and contacting the cover. A simple fiberglass cover could easily be fabricated as well.

 

[jakej]

Bill

B&C have an ANL fuse mount & cover, it's a Blue Seas unit - looks good too

Jake j

 

[lolachampcar]

Slightly off topic but I used one of the wire runs (between main breaker and the master relay) as my current sense element and adjusted the current sense calibration until displayed current draw was accurate. The Dynon current differential amp input has a good dynamic range and will work well simply using the existing wire runs needed in most every install. Just my 2 cents worth.

 

[phvdw]

hi, made it by myself, search for a plastic bottle(found a bottle of sunscreen), cut in half, changing the small screws by long nylon bolts, M4, and use the length of the screws to fasten the half bottle

 

[billythefish]

Thanks everyone!

If I find a perfect solution I'll post it back here!

=bill

 

[jakej]

Thanks everyone!

If I find a perfect solution I'll post it back here!

=bill

Will this be suitable for you ? -- http://www.bandc.biz/anlcurrentlimiterbase-1.aspx

Jake J

 

[ggerhardt]

Slightly off topic but I used one of the wire runs (between main breaker and the master relay) as my current sense element and adjusted the current sense calibration until displayed current draw was accurate.  The Dynon current differential amp input has a good dynamic range and will work well simply using the existing wire runs needed in most every install.  Just my 2 cents worth.

Where did you adjust the current sense calibration? I don't see anywhere that it can be adjusted outside of the 1mV/A setting.

Geoff

 

[dynonsupport]

You cannot adjust this gain factor in the user interface. If you're technically inclined, you can edit the sensor file manually on a computer for the gain your sensor has.

 

[jnmeade]

Can you adjust voltage display that way, also?

 

[dynonsupport]

Yes, you could make a voltage sensor that shows a different voltage than the one measured. Just remember, the EMS is actually a very good voltmeter (about 0.2%), so if you are trying to adjust for what you perceive as a measurement error, it is probably something else. Unless you wired the EMS pin 1 direct to your battery, it isn't measuring your battery voltage, it's measuring the voltage after a series of drops.

 

[ggerhardt]

I seem to be having a problem with my current sensor. Its reading ~1.7x the current it should be. I've got it b/w the alternator and the rest of the plane. To test it, I put my battery charger on the alternator and read the voltage across the amps shunt - 3.7mV. My charger was reading ~4A, so that seemed right. I read the voltage by putting the voltmeter directly on the two ring terminals that were used to connect the wires from the EMS to the shunt. The Dynon was reading 6A, and when I looked in the raw sensor voltage, it said 5.7mV.

The only wrinkle I have is that I have the red voltage measurement wire crimped in the same connector as one of the amps current sense wires. I can't think how that would effect the current reading, tho.

Geoff

 

[dynonsupport]

So that makes it sounds like you're getting the correct amps readings for the voltages you're reading.

 

[ggerhardt]

So that makes it sounds like you're getting the correct amps readings for the voltages you're reading.

No, I must have explained it wrong. When I read the voltage across the amps shunt it is 3.7mV, which is about right for the current that's going thru it. But, when I look at the Dynon raw data for the amps input, its reading 5.7mV, and that's translating to a 6A reading on the display, not the 3.7A that is actually going thru it (or 4A if you round up).

Geoff

 

[dynonsupport]

Our best guess: The charger isn't putting out 4A DC. It's putting out a noisy signal, and we're reading the peak more than the average.

A way to test this: put a more "pure" load on the shunt that doesn't involve the alternator - like running a landing light off the battery and measuirng the voltage at the terminals and comparing then.

 

[ggerhardt]

Our best guess:  The charger isn't putting out 4A DC. It's putting out a noisy signal, and we're reading the peak more than the average.

A way to test this: put a more "pure" load on the shunt that doesn't involve the alternator - like running a landing light off the battery and measuirng the voltage at the terminals and comparing then.

The reason I'm checking into it and trying to troubleshoot it is that I noticed while flying it seemed to be reading high for everything. I noticed it first when I was putting my gear up - the hydraulic pump and my current reading increased over 30A when I raised the gear (gear pump has a 30A breaker).

I see what you're saying with the dirty signal from the charger, but I'm not sure why it would bias the reading high or low. Also, the current it says its putting out agrees with the voltage drop I measure with my voltmeter across the amps shunt.

I'll do some more digging - something's not right.

If I want to just change the scaling factor - where do I find that?

Thanks.

Geoff

 

[dynonsupport]

Geoff,
Sounds like you have done more testing than we realized. Thanks for all the data.

I know you read with a voltmeter, but voltmeters average over up to a second, so they don't catch transients, which is why the possibility of spikes was still on the table.

If you are really convinced the EMS is reading high, we'd really prefer you have it repaired than doing a workaround by adjusting the voltage in the config file. The input should be very well calibrated, and something off by the amount you indicate seems to say something is pretty wrong. It may just be that input, but it may be affecting other things too.

Give us a call or an email when it's easy for you so we can get your EMS tested and repaired if needed.

 

[ggerhardt]

I checked the voltage reading at the DB37 that plugs into the EMS (across pins 24/25 that bring the amps shunt voltage in). The voltage across pins 24/25 was 2.7V whereas the Skyview raw data voltage on the sensor debug page was indicating 4.3V when I plugged the DB37 back into the EMS box.

I again used by battery charger connected to the alternator to simulate charging across the amps shunt. I understand your concern my voltmeter and the Skyview may have different low-pass filtering - I'm not sure I agree that it would result in a DC offset. Also, this high reading is consistent with a generally high current indications I've been seeing from the Skyview during flight testing.

Perhaps I should send the EMS back for repair. I understand you're working on a fix for the EMS that reduces temperature spikes in the thermocouple readings during PTT, tho. I have this issue as well (~10-20F increase). Rather than send my EMS in now, should I wait until you have a fix for this? And in the meantime, just adjust the current scalar to give correct current readings?

Thanks.

Geoff

 

[dynonsupport]

I checked the voltage reading at the DB37 that plugs into the EMS (across pins 24/25 that bring the amps shunt voltage in).  The voltage across pins 24/25 was 2.7V whereas the Skyview raw data voltage on the sensor debug page was indicating 4.3V when I plugged the DB37 back into the EMS box.

I again used by battery charger connected to the alternator to simulate charging across the amps shunt.  I understand your concern my voltmeter and the Skyview may have different low-pass filtering - I'm not sure I agree that it would result in a DC offset.  Also, this high reading is consistent with a generally high current indications I've been seeing from the Skyview during flight testing.

Perhaps I should send the EMS back for repair.  I understand you're working on a fix for the EMS that reduces temperature spikes in the thermocouple readings during PTT, tho.  I have this issue as well (~10-20F increase).  Rather than send my EMS in now, should I wait until you have a fix for this?  And in the meantime, just adjust the current scalar to give correct current readings?

Thanks.

Geoff

Geoff:

Since this is an apparently an individual support issue, let's transition this discussion over to Dynon Tech Support - support@dynonavionics.com or 425-402-0433. They can discuss your specific repair options. If you email (preferred), please include a link to this discussion so the Tech Support individual can get up to speed with what's already been discussed.