Is anyone interested in the details of a homebrew four-zone DC volt/amp panel project?
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| Author: | GTBecker [ Fri Sep 03, 2010 11:40 am ] |
| Post subject: | Volt/Amp panel project |
Is anyone interested in the details of a homebrew four-zone DC volt/amp panel project?
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| Author: | fred111 [ Mon Sep 06, 2010 9:21 am ] |
| Post subject: | Re: Volt/Amp panel project |
Yes. Looks interesting. |
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| Author: | millhaven_nice_guy [ Tue Sep 07, 2010 9:38 am ] |
| Post subject: | Re: Volt/Amp panel project |
This also looks interesting to me... It would be nice to be able to monitor the house battery voltage and amp draws at the flick of a switch. |
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| Author: | jnizi [ Tue Sep 07, 2010 1:21 pm ] |
| Post subject: | Re: Volt/Amp panel project |
So what does the RS-232 port do on the chassis? Is that a control or monitoring buss? |
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| Author: | GTBecker [ Tue Sep 07, 2010 1:36 pm ] |
| Post subject: | Re: Volt/Amp panel project |
jnizi wrote: ... what does the RS-232 port do... It's not RS232, but I used a serial cable to conveniently carry eight shielded shunt wires and a ground to the meter panel. I am working on an enhancement, though, that will provide eight channels of data, four each of voltage and current, to a helm PC via Bluetooth. I'll put a project description together with more photos and schematics. |
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| Author: | jnizi [ Tue Sep 07, 2010 2:19 pm ] |
| Post subject: | Re: Volt/Amp panel project |
Very Cool. I wish I had the time to work on something like this. |
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| Author: | GTBecker [ Wed Sep 08, 2010 11:21 pm ] |
| Post subject: | Re: Volt/Amp panel project |
I have an electrically and electronically highly-modified boat. I develop marine instrumentation and my '99 258 Vista serves as one of my workshops, so clean, reliable and adequate power is important. I currently use four Group 27s, two each for House and Start/Run, two chargers (an Iota DLS45 charger/supply, and a Guest trolling charger for backup on Start/Run), two Yandina C100 ACRs, a number of non-stock fuseblocks and switches and a lot of 8Ga wire. Still, after gradually adding and changing these things over several years, I had no real way of knowing just what the current states of the power systems were. I considered purchasing Blue Sea battery monitoring products but stopped when I got to $700, and after that expense I'd still need to exert days of installation time. Maybe worse, for their digital monitor the shunts need to be in the return lines which, for me, would have been difficult to do (and I have no idea how one can insulate the alternator from the engine to get at its low side). So, I set about doing my own four-zone volt/amp meter. I opted for D'Arsonval (old-style analog moving-needle) meters since I had them on hand. Were I to do it again, I might use digital panel meters since an expanded-scale voltmeter proved harder than I thought - and is unnecessary with a digital display - but digital meters aren't perfect, either; needle motion can be very telling but changing digits can be just a blur. The meters I used are inexpensive; time will tell if they are sufficiently rugged. I got them from All Electronics, but they can be found on ebay, directly from Hong Kong, for less. The ammeter is intended to match 30-Amp shunts they also sell. http://www.allelectronics.com/make-a-st ... 0A//1.html I use three 30A shunts for the House, Start/Run and Charger circuits I wanted to monitor - and a 100A/50mV shunt, modified to 75A/75mV, for the alternator circuit. The shunts are in a box that mounts on the engine compartment bulkhead close to my house batteries, except for the alternator shunt which I located right at the alternator. Two wires, both fused, run from each shunt to the meter panel in the cabin, where they are switched in pairs to the meters. I used a common DB9 serial cable (nine conductors plus shield) to make those connections easy. I found that the ammeter was too inaccurate for my taste, a little low, so I added a small 50-ohm potentiometer in parallel with the internal 4.7-ohm wirewound resistance in the meter movement itself to be able to adjust it. Below are both a simplified shunt box schematic and another, a partial schematic of the actual implementation in my boat. The expanded-scale voltmeter circuit requires some explanation. Fundamentally, it is two fixed voltage regulators which, combined, subtract 10 volts from the sample voltage; the resulting voltage is then displayed on a five-volt fullscale meter ( a 1mA meter and 5k series resistance) so it shows 10 to 15 volts over the scale range. Since the regulators are inherently very accurate no calibration is required. I use the positive-side ammeter shunt sample wire to sample voltage. Since the regulators draw a small current (about 9mA), a very small error voltage would result - wreaking havoc on the ammeter (which measures only 75 millivolts fullscale). So, electronic engineers reading this will recognize an emitter-follower on that sample line, reducing the ammeter error to essentially zero; a diode drop on the low-side regulator corrects for the 0.6v base-emitter junction drop. A DC-DC converter assures that the emitter-follower collector voltage is always greater than the sample voltage, so the regulator current comes from it, not from the sample line; the converter is powered by cabin DC since it cannot be powered by a shunt sample line. I used the stereo memory keep-alive power line, which was convenient. Alternatively, a 3P4T switch can be used to switch a separate voltage sample wire for each source, but that requires four more wires between the shunt box and the meter panel. I built the voltmeter on a piece of Radio Shack circuit board. If this level of construction is more than you care to do, a standard zero-to-15 volt meter results from a 1mA meter and a 15k series resistor, and is easy to build. Either way, the meter can be rescaled by removing and scanning the original scale, editing the image, and printing, carefully gluing and resecuring the new scale to the meter face. I made both the 10-to-15 volt scale and a dual-scale ammeter with Paint, in Windows. I intend to add to the panel display a small circuit board that will house a processor and Bluetooth transceiver, providing wireless data to the boat's helm PC. A small application program will watch that data, monitoring, displaying and logging it.         
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