"Watt's Up" February 13, 2009, 04:33:41 pm Yahoo Message Number: 99284Hello all, Have you used "Watt's Up"? It's a reasonably priced battery monitor, $60.If you have, what's your recommendation?Thanks,Sam
Re: "Watt's Up" Reply #1 – February 13, 2009, 05:25:20 pm Yahoo Message Number: 99287"Have you used 'Watt's Up'? It's a reasonably priced battery monitor, $60."A $60 battery monitor would certainly be very welcome, since the Link-10 and XBM many of us rely on are on the pricey side ($215-$250). I looked over the specs on "Watt's Up" and the similar "Doc Wattson" battery monitor. Although intended for radio controlled models, and limited to 50 amps continuous power (no high-powered alternators or inverters, please!), they might be adaptable to RV use in low- to medium-power applications. I see one big problem, however: unlike the Link-10 and XBM, which come with a precision shunt that mounts in the battery compartment and a separate readout that can be placed in your living quarters, Watt's Up and Doc Wattson are one-piece units with the shunt *built in*... so they would have to be mounted in the battery compartment where you couldn't see them in normal use.It seems to me that without the ability to use a separate shunt and thus mount the readout where you can see it all the time, a battery monitor such as these would be of very limited usefulness. Now, *maybe* a clever person could hack one of these units to use a separate shunt. Or maybe the manufacturer, RC Electronics, Inc., could be persuaded to produce a version with this capability.Andy Baird http://www.andybaird.com/travels/
Re: "Watt's Up" Reply #2 – February 13, 2009, 08:12:49 pm Yahoo Message Number: 99291Quote I see one big problem, however: unlike the Link-10 and XBM, which come with a precision shunt that mounts in the battery compartment and a separate readout that can be placed in your living quarters, Watt's Up and Doc Wattson are one-piece units with the shunt *built in*... so they would have to be mounted in the battery compartment where you couldn't see them in normal use. If I were to install it, I would simply "move" the battery negative post to where I want the display installed. In my planned case it would be a one 6 foot long cable behind the wall.Sam
Re: "Watt's Up" Reply #3 – February 13, 2009, 08:20:28 pm Yahoo Message Number: 99293Correction: If I were to install it, I would simply "move" the battery posts to where I want the display installed.
Re: "Watt's Up" Reply #4 – February 13, 2009, 10:28:55 pm Yahoo Message Number: 99297Quote Hello all, Have you used "Watt's Up"? It's a reasonably priced battery monitor, $60.If you have, what's your recommendation?Thanks, Sam Not having one in my hand and only scanning the on-line instruction manual, I believe it has a basic problem. The Watt's Up and the Dock Watson units both appear to expect the current to flow only in one direction through the monitor. In each example shown on page 19 of the manual, the current flows from the source side of the meter toward the load side. Their clever simulator does not allow one to create a reverse current flow so one cannot quite tell for sure. The 65 amp- hour limitation of the Watt's Up unit is really too small for RV use unless if the house battery is very small. The typical LD (2 ea T105 batteries) can safely discharge 100 amp-hours without problems; more, if one is willing to accept the shortened battery life.Having said that it has limitations, I'm impressed with what they managed to get into the package for the price. I've pondered how I could get an amp-hour meter for studying solar panel output to see if my calculations even remotely agree with reality. This device should be able to do that job for cheap. Or, one could rig it up so it could be plugged into the fuse panel to monitor DC appliance current usage. One could really find out how many amp hours the furnace actually uses on a cold night.Linley
Re: "Watt's Up" Reply #5 – February 13, 2009, 11:47:24 pm Yahoo Message Number: 99300"If I were to install it, I would simply 'move' the battery posts to where I want the display installed. In my planned case it would be two 6 foot long cables behind the wall." Adding 12 feet of cable to your 12V system is possible, but probably not practical or economical. You'd have to use VERY heavy cable to avoid ruinous power losses. Off the top of my head, I'm thinking AWG 0 or 00, even if your power usage (in amps) is modest--as it would have to be with the limitations of these devices. At today's copper prices, the cable to do this could cost you nearly as much as the "Watt's Up" monitor. If you tried to use lighter-gauge cable--like the skinny wires on the monitor itself--you'd end up with severe resistive losses (and possibly dangerous overheating) as soon as you tried to pull any real current from your batteries.Also note Linley's comment: it's not clear that these devices can measure current flowing in both directions, which is essential for a useful RV battery monitor.Overall, I don't believe these devices are practical for your purposes... but I do think this company has the ability to produce a monitor that is, and do so at a moderate price. It's just a question of wanting to. The fact that they sell high-current shunts on their website (although curiously, there doesn't appear to be any way to connect them to their monitors) shows that they understand what needs to be done: put the shunt in the battery compartment, with a few inches of heavy cable connecting it to the battery... then put the monitor where it'll do the most good, and run lightweight wire to it from the shunt. Only by separating these two functions can you make a really practical battery monitor for an RV.Andy Baird http://www.andybaird.com/travels/
Re: "Watt's Up" Reply #6 – February 14, 2009, 07:28:58 am Yahoo Message Number: 99304Quote Their clever simulator does not allow one to create a reverse current flow so one cannot quite tell for sure. This is my main concern too.QuoteThe 65 amp-hour limitation of the Watt's Up unit is really too small for RV use ... I am not worried about this. I only have a small 200w inverter. I cannot think of drawing more than 30 amp at any time.QuoteHaving said that it has limitations, I'm impressed with what they managed to get into the package for the price. Me too.QuoteOr, one could rig it up so it could be plugged into the fuse panel to monitor DC appliance current usage. One could really find out how many amp hours the furnace actually uses on a cold night. Yes, it's a DC "Kill A Watt"Sam
Re: "Watt's Up" Reply #7 – February 14, 2009, 07:38:01 am Yahoo Message Number: 99305QuoteAdding 12 feet of cable to your 12V system is possible, but probably not practical or economical. Somewhere in my garage, I have several old heavy duty jumper cables. So my wiring cost would be zero :-)Sam
Re: "Watt's Up" Reply #8 – February 14, 2009, 09:17:02 am Yahoo Message Number: 99310QuoteYes, it's a DC "Kill A Watt" I was just going to mention this in response to Linley's post.Here's the link to the product: http://www.p3international.com/products/special/P4400/P4400-CE.htmlIf that doesn't come through whole, just go to www.p3international.com and search for the Kill A Watt.Linda Hylton http://map.datastormusers.com/user1.cfm?user=1167 http://earl-linda.blogspot.com/
Re: "Watt's Up" Reply #9 – February 26, 2009, 08:05:09 am Yahoo Message Number: 99647Quote manual, I believe it has a basic problem. The Watt's Up and the Dock Watson units both appear to expect the current to flow only in one direction through the monitor. Just an update: I pored over the user's manual and found the confirmation: Watt's Up ONLY measure POSITIVE voltage and current. Oh well...Sam
Re: "Watt's Up" Reply #10 – March 06, 2009, 08:21:37 am Yahoo Message Number: 100047QuoteJust an update: I pored over the user's manual and found the confirmation: Watt's Up ONLY measure POSITIVE voltage and current. Oh well... Final update: I've sent questions to Watt's up, but they did not respond. I've found two more similar products, Medusa Power Analyzer and Whatt Meter. All three basically use the same design. The Medusa and Whatt do show negative current up to -30Amp and -10Amp, respectively. However, all three have a VERY SIGNIFICANT problem which is not documented in their user's manuals: They all use a small internal shunt that has a LARGE voltage drop. I found out through correspondences with the Medusa Power Analyzer that at 30amp current, the voltage drop is 0.65 volt. That said, they are still great products for a quick check on DC equiqment, but not as a permanently installed battery monitor for motorhomes.Sam
Re: "Watt's Up" Reply #11 – March 06, 2009, 04:11:06 pm Yahoo Message Number: 100071A guy could make his own ammeter, I suppose, by contriving a 1 milohm (0.001 ohm) shunt, maybe from wire or by paralleling, say, 10 10 milohm resistors, or something, and then put p
Re: "Watt's Up" Reply #12 – March 06, 2009, 06:39:39 pm Yahoo Message Number: 100076"A guy could make his own ammeter, I suppose, by contriving a 1 milliohm shunt..." There's no need, really, because the 500 amp precision shunt used by the Link-10, XBM and other battery monitors is readily available for a little over thirty bucks:http://www.rc-electronics-usa.com/buy-current-shunt.html> If that were all there was to it, you could build a homebrew battery monitor for fifty bucks or so instead of paying a couple hundred for a commercial one. But a shunt and a meter can only tell you how much current is flowing at a given instant. While that can be handy for measuring how much power your appliances consume, it tells you nothing about your battery's state of charge, because that depends on how much power was used *for how long*. What a commercial battery monitor such as the Link-10 has is the ability to *record* current flow in digital format. It keeps a running total, constantly adding every amp-second that goes into or out of your battery bank. Its computer knows the total capacity of your batteries (because you tell it during setup), and 24 hours a day it adds and subtracts from that total, as you add power and use power. At any given instant the computer knows exactly how much power is in the batteries--not by measuring the voltage, which is all but meaningless for practical purposes, but by saying "OK, the batteries can store 225 amp-hours, and we had a full charge yesterday afternoon at 3:05 p.m.... but since then we've used up 74.5 amp-hours and added back in 26.2 amp hours from the solar panels, so that leaves us with 176.7 Ah, or 78% of full capacity." No simple meter, digital or analog, can tell you this, because they can't integrate power use over time. Only a computer can do that. That's why a good battery monitor costs more than just a shunt and a meter. Does it have to cost as much as the Link-10 and XBM do (about $220-$250)? I'd like to think not. The $60 Doc Wattson meter shows that most of the needed intelligence can be put together for a very modest cost. From what I know of the technologies involved, I suspect that Doc Wattson's maker could build a functional equivalent of the Link-10 for no more than $75, if they wanted to. But let's face it, this is a limited market. :: sigh :: That means prices are likely to stay high, since unit sales are low. At least, I'm sure that's the way manufacturers see it. They have to charge enough to recoup their research and development costs.Andy Baird http://www.andybaird.com/travels/
Re: "Watt's Up" Reply #13 – March 07, 2009, 08:14:57 am Yahoo Message Number: 100090QuoteAt any given instant the computer knows exactly how much power is in the batteries--not by measuring the voltage, which is all but meaningless for practical purposes, but by saying "OK, the batteries can store 225 amp-hours, and we had a full charge yesterday afternoon at 3:05 p.m.... but since then we've used up 74.5 amp-hours and added back in 26.2 amp hours from the solar panels, so that leaves us with 176.7 Ah, or 78% of full capacity." "The computer THINKS it knows exactly..." would be a more accurate statement. There is no way to be exact when the initial parameter is itself a guesstimate. Battery's capacity is not exact even brand new, regardless of how expensive it is. Other factors that prevents "exactness" are ambient temperature, battery's age, rate of charge and discharge. Most significant is the basic characteristic of all batteries: You always get out less energy than you put in.Sam
Re: "Watt's Up" Reply #14 – March 07, 2009, 08:32:24 am Yahoo Message Number: 100092Quote from: bliffle"John, I did not make my own shunt. I bought a big, heavy precision Empro 100amp/100mv shunt ($10) and couple it to 2 cheap digital multimeters ($13 for both). So I now have a home made rudimentary battery monitor for less than 25 bucks.SamA guy could make his own ammeter, I suppose, by contriving a 1 milohm (0.001 ohm) shunt, maybe from wire or by paralleling, say, 10 10 milohm resistors, or something, and then put pin jacks at each end and use a DMM capable of reading millivolts. Lacking such a DMM, one could employ a D'arsonval voltmeter mechanism, which should have a sensitivity of 1000 or 10,000 ohms/volt or thereabouts, which for a full-scale reading of 100 millivolts (reflecting 100A thru a 1 milohm resistor) would be 10 or 100 ohms, which wouldn't bias the reading much. I think you can cannibalize a suitable D'arsonval movement from a $10 or $20 Analog DMM from HarborFreight or radio shack. Maybe RS even has just the movement available. Probably the resistance of the movement is much less than the desired 10 or 100 ohms so you have to add appropriate series resistors. Just make sure the 1 milohm resistor can't burnout under 100A current! I'd probably start making that 1Milohm resistor by cutting up some tincan sheet metal, making a small dumbbell-shape such that the resistance is determined by the narrow waist. It's hard to measure such low resistance, but one can use the D'arsonval meter in various ways to assist that.John
Re: "Watt's Up" Reply #15 – March 07, 2009, 08:59:00 am Yahoo Message Number: 100093Quote From: mynetsig To: lifewithalazydazerv@yahoogroups.com Sent: Saturday, March 07, 2009 6:14 AM Subject: [LD] Re: "Watt's Up""The computer THINKS it knows exactly..." would be a more accurate statement.There is no way to be exact when the initial parameter is itself a guesstimate. Battery's capacity is not exact even brand new, regardless of how expensive it is. Other factors that prevents "exactness" are ambient temperature, battery's age, rate of charge and discharge. Most significant is the basic characteristic of all batteries: You always get out less energy than you put in.SamSam,We're splitting hairs, I think. What Andy wrote is essentially correct. His use of the word "exactly" may not have been the very best choice, but it certainly isn't far off the mark.The *real* battery monitors in question take into account battery temperature, type, initial amp hour capacity (as stated by the manufacturer), and doubtless have algorithms for discharge and charge rate as well. They also account for the battery banks ineffeciency of having to put in more energy than you get out. Further, they "learn" and self-adjust in use to account for such variations in battery parameters. One could argue that they are not 100% accurate and they would be correct. The same arguement might be made for fuel gauges, the "ScanGauge", your speedometer, or any number of indicators and gauges in use today. None of which is a condemnation of these devices, as they may be the very best, practical, and accurate method of gaining the required information. This is the case with the Link-10 and similar battery monitors. Comparing a battery monitor to a voltmeter or ampmeter, though both of these have their place, is like comparing a skateboard to a motorcycle.all the best,bumper Yonder Minden, NV ]
Re: "Watt's Up" Reply #16 – March 07, 2009, 09:04:12 am Yahoo Message Number: 100094Quote At any given instant the computer knows exactly how much power is in the batteries--not by measuring the voltage, which is all but meaningless for practical purposes, but by saying "OK, the batteries can store 225 amp-hours, and we had a full charge yesterday afternoon at 3:05 p.m.... but since then we've used up 74.5 amp-hours and added back in 26.2 amp hours from the solar panels, so that leaves us with 176.7 Ah, or 78% of full capacity.""The computer THINKS it knows exactly..." would be a more accurate statement. There is no way to be exact when the initial parameter is itself a guesstimate. Battery's capacity is not exact even brand new, regardless of how expensive it is. Other factors that prevents "exactness" are ambient temperature, battery's age, rate of charge and discharge. Most significant is the basic characteristic of all batteries: You always get out less energy than you put in. All of these factors can be adjustments by the program if the battery technology is dialed in, and most units include a battery temperature sensor... except precise info regards a specific brand & model. Although the simple monitors in this discussion may not be include enough factors to be considered a perfect mirror of the state of charge, I suspect that they probably succeed to better than 90% accuracy under most circumstances. With more precise battery characterization and high sophistication, the ECU in a Prius can probably predict exactly how much your battery has deteriorated. After all, there is nothing preventing these programs from 'learning' the same way the vehicle's ECU also adjusts driving parameters based on engine performance.Steve
Re: "Watt's Up" Reply #17 – March 07, 2009, 10:14:26 am Yahoo Message Number: 100099All true, sorta, but there is another way to integrate current over time: with a mercury accumulation meter. You'd be surprised how much military electronic equipment contains these little dudes (don't ask me how I know because I'd have to kill you). As current passes thru from the small memory batteries and such mercury moves from one end to the other and visually indicates state of charge. Clumsy, but simple and cheap. They're commercially available at modest cost. All a guy has to do is figure out a simple resistor network to properly apportion the current. Of course they are difficult to reset to zero and will eventually drift off calibration thru charge/discharge cycles.John
Re: "Watt's Up" Reply #18 – March 07, 2009, 10:35:26 am Yahoo Message Number: 100102"there is another way to integrate current over time: with a mercury accumulation meter." Wow--I haven't seen one of those in close to forty years, and had forgotten all about them. :-) The only question is whether they are linear in both directions. To be useful, a battery monitor must record current flow in both directions--into the battery bank and out of it. As for the rest... bumper put it best. You can say that my use of "exactly" was hyperbole if you like, but the fact remains that the XBM and Link-10 come very close. They compensate for battery temperature, rate of charge/discharge, and a good deal more. (The XBM, for example, has an adjustable setting for Peukert's constant.) These are sophisticated devices that adjust for many variables, and automatically recalibrate themselves as the batteries age. Yes, you tell them the amp-hour rating initially, but from then on they determine it on the fly. If you're really interested in how these devices work, I suggest downloading the XBM owner's manual (PDF document) from Xantrex's website. I think you'll be impressed by just how smart these devices are, and how many factors they take into account to arrive at an accurate assessment of state of charge. I have pretty good knowledge of both hardware and software, but these sophisticated commercial monitors go way beyond anything I could hope to achieve in a homebrew project. :-)Andy Baird http://www.andybaird.com/travels/
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