Greetings,

New to this forum, not new to fora.

The application is a motorhome. Diesel engine with alternator. Two lead acid battery banks ("house" and "chassis") with intelligent battery isolation manager which parallels the banks when there's a charge source on either and the other needs charging. Smart 120V AC powered battery charger.

Condition is while driving and in need of AC. There's an automotive style dash AC which keeps the cockpit cool, the house behind it has two roof mounted 120V AC's. Currently the only power source is the on-board diesel powered 6000W AC generator. Running this for just a 1500-2000W load for all the hours of driving is not the most efficient.

My objective, and there is precedent, is to run one of the roof AC's through the 3000W pure sine inverter from the house bank (450Ah total). Keeping it charged would be on the alternator. Current alternator size is 160A. This would need to be increased. A 200A alternator of the same model is a direct swap out. According to the manufacturer (Delco Remy) it is suitable for continuous duty at or near it's rated output, provided it gets adequate cooling.

This may or may not be enough. The AC load would be 12A 120VAC, 1440W = 120A 12VDC. The chassis has a DC load to run. How much I don't know.

Here's the question (yup, there is one).....

The FIRST thing I want to do is measure, real time, the output of the alternator as currently installed. I need a DC ammeter rated to around 300A that can be installed in the POSITIVE output of the alternator, with a readout 40 feet away...(rear engine setup).. I would like something that I can permanently install in/on the dash. So far everything I have found needs to be in the negative cable to a battery, but this is not practical as there is output going from the alternator to multiple locations. I need the actual output at the ALTERNATOR. Second problem is that a twisted pair to a shunt would travel the 40 feet to a readout and be subject to all kinds of interference.

Suggestions? Thank you!

 

Why can't you put a 300 Amp shunt between the Positive wire the Alternator and the Battery?
Most require Negative Ground, some don't.

Shunt Adapter for DC Digital Ammeter positive side shunt applications, such as alternator measurement ...
https://www.bluesea.com/products/8242

Why can't you use a shielded twisted pair between the Shunt and the Dash Display?

 

Well, all the instructions with ammeters say it's important that it's in the negative connection.... My question is "Is it?" and possibly why. The twisted pair would travel 40 feet which is quite a ways and I'm afraid there would be quite a bit of interference, voltage loss etc.

 

Most Shunts require negative ground, some do not.
Check out the URL link in my message #2, when placing the Shunt in the Positive Wire.

 

Ah.... the word of the day is "shunt shifter"... thank you.

 

The Tri-Metric Monitor allows 100 Feet UTP wire between the Shunt and the Digital Monitor.

 

The Tri-Metric Monitor permits 100 Feet UTP wire between the Shunt and the Digital Monitor. But is that true the twisted pair to a shunt would travel the 40 feet to a readout and be subject to all kinds of interference?

 

I think you are making a terrible mistake. I think you will regret putting the extra load on your tractor engine.

Keep the house power isolated. Upgrade or modernize(micro-control) that system.

Leave the carriage alone.

Most motor homes are not owned for very long. It's just a phase for many, like a cock-eyed boat.

A carriage modification will de-value it.

 

How about a Hall effect current sensor, such as this? You could have a small signal-conditioning circuit close to the sensor and run the long cable from the circuit's output to the dash.

 

OK... thanks for the ideas. I've ordered a Hall effect gauge, will have to see if lengthening the sensor wires will work....

As far as messing with the engine.... upgrading the alternator will not degrade the value, quite the opposite....

And, I've made a few "mods" already..... ;-)

https://dragonship.blog/

 

will have to see if lengthening the sensor wires will work....

You might get away with that. If you're only interested in the current averaged over a 1 sec or so period then some heavy low pass filtering, perhaps at both ends of the cable, should suppress any interference.

 

Yes, 1 sec average is more than plenty...
How would I do "heavy low pass filtering" ? Fine electronics is not my wheel house.
Thanks.

 

It's not the shunt that's the problem, it's the actual digital meter.

The meter would have to be powered to be able to read it. DATEL used to be great, now it looks like they suck too.
Here's http://www.datel.com/data/ps/pm35-series.pdf a datasheet,

Page #2:
2. Units can only accept single-ended inputs, where the negative terminal of the input voltage (–Vin) is connected to power supply ground –Supply
and
Differential Readings Adjustable from 10 to 1999

in the same breath.

Who, what, where do you believe?

Even this:
Three Input Ranges: 0
–±200mV; 0
–±5V; and 0
–±10V

Then the fine print:
The 0-5V and 0-10V input ranges both support adjustment ofdifferential ranges (i.e., highest reading minus the lowest reading) from “10” to “1999”. These two ranges also support an offset adjustment range of ±1800 counts. A fixed-gain input range of 0
-200mVdc provides additional signal conditioning flexibility

This meter doesn't like to scale 0-200 mV inputs. This is bad for shunts too. But you can convert a 0-5V signal to engineering units which is the common thing to do.

In theory, you could use a low noise Isolated DC-DC converter to make these work.

There are high-side current sense amplifier IC's, but thatt the IC only, not the circuit. Here https://www.digikey.com/en/product-...MI6cSAj6KW4QIVBEGGCh1_AwhGEAAYASAAEgI5tPD_BwE current is unidirectional.

ST TSC103

 

How would I do "heavy low pass filtering" ?

Capacitor from the Hall sensor output to ground at the Hall end of the cable, resistor in series with the signal wire at the dash end of the cable, capacitor from the dash end of that resistor to ground. Component values chosen to suit Hall sensor spec and averaging period. Signal amplification probably needed at the dash end.

 

Yes, 1 sec average is more than plenty...
How would I do "heavy low pass filtering" ? Fine electronics is not my wheel house.
Thanks.

If fine electronics is not your wheel house then ...
Ask ORE, or other manufacturer, to fabricate a longer 40' extension cable, instead of the normal 12' cable.

http://www.offroadengineering.com/product-12V-DC-Monitoring-System.html

Part # DPS-DCS35-300-1-K1 (single sensor kit)
Kit includes:
one DPS-DCS1 digital volt / amp / alarm meter
one +/-300 amp DCS35-300-1 current sensor
one 12 ft. harness with DCS connector.

You must use Waterproof connectors under-the-hood.
And all components must be rated for very high temperatures and very low temperatures.

 

THAT is helpful... thank you!

 

There is some useful general info on this http://www.datelmeters.com/ website.

the problem with most DPM's is that the negative power supply is the negative reference and you can't change that.

If you have to measure charging and discharging currents, the ammeter has to be able to show both polarities.

Operating the DPM on an isolated DC-DC converter may get you only halfway there.

 

"This may or may not be enough. The AC load would be 12A 120VAC, 1440W = 120A 12VDC"

Just as a warning from, my experience, running your alternator under that heavy a load in the already hot engine compartment will greatly shorten your alternators life. You will likely need to keep a spare next to your bed. Im just gonna guess that it will be cranking out around 200°F+. That is without any help from the radiant engine heat. A generator may be ineffecient but will likely be more cost effective compred to maintenance.
Good luck,
Jason

 

My friends Ford F-450 came with a 200 Amp x 14 Volt = 2,800 Watt alternator.
Still running strong
1,440 Watts would only be a 50% load.

 

"This may or may not be enough. The AC load would be 12A 120VAC, 1440W = 120A 12VDC"

Just as a warning from, my experience, running your alternator under that heavy a load in the already hot engine compartment will greatly shorten your alternators life. You will likely need to keep a spare next to your bed. Im just gonna guess that it will be cranking out around 200°F+. That is without any help from the radiant engine heat. A generator may be ineffecient but will likely be more cost effective compred to maintenance.
Good luck,
Jason

Also your battery isolator will be flowing all those amps as well and may also have a shorter life span. Depending on its ratings of course
-Jason