Wiring a digital ammeter

[bmc5733946]

I have a digital ammeter I would like to wire into a Saprisa charging system on a 1989 Mille GT.  All the Saprisa systems being presumably the same I'm using a wiring diagram for a California III.

The ammeter and shunt.
https://www.amazon.com/gp/product/B00BYQSXPI/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

The wiring diagram.
http://www.thisoldtractor.com/guzzi007/pdfs/1987_California_III.pdf

The question.
Can anybody tell me where to put the shunt to get appropriate readings of the charging system??

Brian

[sbaker]

Well the Amazon diagram only shows 2 batteries... I Presume you have only 1.. Therefore follow this diagram. The Shunt interrupts the negative circuit between the Battery and the alternator..

[Testarossa]

As noted in the previous thread, don't put the ammeter on the negative side of the battery or the starting current will fry it. It needs to be wired into the positive side of the battery.

I don't understand the Cal II wiring diagram either. I use the 1000S diagram. It shows a red-black wire coming out of the regulator to feed power to the whole system, eventually connecting via a red wire to the battery + terminal, and that's where I'd wire in the ammeter.  The red wire between the regulator and alternator is NOT what you want.  Unless someone knows the real deal on Saprisa.

[Wayne Orwig]

Lift the ground wires off of the negative side of the battery. Connect them to the shunt. Connect the other side of the shunt to the negative side of the battery. Attach the heavy red and black wires to the shunt. Connect the light red wire to a switched positive connection. 
Basically, pass ALL of the negative/ground side battery power through the shunt. Attach the heavy red/black wires to the shunt to measure the power going through the shunt to and from the battery.

BUT, that means that all of the starter current, which will be over 100 amps, will be passed through the shunt. That is probably not an issue, but they don't really spec that. If it was a POSITIVE side shunt, it would be easier to isolate the starter motor current.

[bmc5733946]

Wayne is the shunt a one way device, current cannot pass through it either way? Could it be reversed to work on the positive side?  Then reverse the wires going to the meter to read correctly?

So the 100amp rating on the shunt is the current it can safely carry?  It could possibly carry more current on an intermittent basis (the starter load)?  If I obtained a 300amp shunt or even larger, then it could work on the negative side, safely?  I guess I could hook all this up and just try it, this was not a major investment.  I would like to understand the workings of a shunt but everything I found on google was over my head.

Brian

[pressureangle]

The shunt needs to be in the charging wire between the alternator and battery positive terminal. You can't use it between the starter cable and battery, because charging voltage comes into the battery only, but starter current goes out and the meter is directional. This is all good if you're only measuring charging current.

You did note that the ammeter says in the listing that the shunt is not included?

[bmc5733946]

I did however purchase both the digital ammeter and recommended 100amp shunt.  Yes I understand the meter is directional, is the shunt also?  Where do I locate this wire between the alternator and battery positive?  I think maybe I can use the red/black between regulator and fuse box?  If I can use that wire I can probably use a smaller shunt, 40amps or so?

Brian

[Testarossa]

I think maybe I can use the red/black between regulator and fuse box?  If I can use that wire I can probably use a smaller shunt, 40amps or so?

That's where I would put it.  And if it goes there, the shunt can be a lot smaller than 100 amps -- just make sure it will handle about 10 amps more than the fuse, so the fuse blows first.

If you have a bi-directional ammeter -- one that will display both positive and negative amps (power going to the battery vs power coming from), you could attach one end of the shunt to the battery terminal and all other positive battery connex to the other end of the shunt. Then when loads exceed what the charging system can produce, you'll see a negative reading (net drain on the battery).  When the system is charging the battery at a rate that exceeds the drain, you'll see a positive reading.  When everything balances, near 0.

[bmc5733946]

I'll hook up a test rig using a DeWalt battery and a headlight bulb, try it both ways.  Gee, what a nice fire and very warming.  May I'll fuse the test bed eh!!

Brian

[Wayne Orwig]

Wayne is the shunt a one way device, current cannot pass through it either way? Could it be reversed to work on the positive side?  Then reverse the wires going to the meter to read correctly?

So the 100amp rating on the shunt is the current it can safely carry?  It could possibly carry more current on an intermittent basis (the starter load)?  If I obtained a 300amp shunt or even larger, then it could work on the negative side, safely?  I guess I could hook all this up and just try it, this was not a major investment.  I would like to understand the workings of a shunt but everything I found on google was over my head.

Brian

The shunt is a simple block of copper (or brass or something conductive). Often with a little groove or cut filed into it to calibrate it. Basically, a calibrated piece of heavy wire.
So the SHUNT can go anywhere safe. But the meter that you have implies that the shunt HAS to be in the negative side. It is often the case that when you design an analog input that works at or below ground level, it isn't going to tolerate inputs at or above the positive level.

A 300 amp shunt likely wouldn't have the required .075 volt at 100 amp output.

Even better. Clip this on any wire that you wish to measure. Done.

https://www.amazon.com/bayite-Digital-Current-Voltage-Transformer/dp/B01DDQM6Z4/ref=pd_sbs_263_4?ie=UTF8&pd_rd_i=B01DDQM6Z4&pd_rd_r=7HCVB3NMGF54N7BRBQMG&pd_rd_w=8xNkv&pd_rd_wg=72xPq&psc=1&refRID=7HCVB3NMGF54N7BRBQMG

[bmc5733946]

You sir are a GOD!!!!  That solves all my problems!!!  Even I can't screw up that installation!!!!  Installation is not so permanent that I can use it on different vehicles.  Aint technology wunnerfull!!!

Thank you so much!!

Brian