I didn't want to hijack Brad's Trimetric 2025-RV Installation (http://www.foreforums.com/index.php?topic=19256.0;topicseen) so started a new one.
I'm about to install a Trimetric I bought off of ebay. The one I purchased came with a 500a shunt. I knew the Trimetric can handle 2 batteries but mistakenly believed a 2nd shunt was required so purchased a 2nd shunt off ebay at the same time. After reading the install instructions I now know it does not. (it only monitors voltage on the 2nd battery shunt not required)
So I'm trying to decide if I should resell the shut (at most likely a loss) or wire it into my system. Here is what I'm thinking. I could put one shunt on each of my 2 house batteries and wire in switches to select which battery to monitor or just go all in and buy another Trimetric and wire it in to monitor the house batteries separately.
Just looking for some input on if this is way overkill or will it be incredibly useful and why didn't anyone think of this before! ;D
Let the argument discussion begin!
see ya
ken
I'd sell it. Surely someone else will want a Trimetric, and they do sell them sans the shunt, right? A second one in the coach doesn't sound very useful to me.
We have two 8D8G house batteries and have separate 500 amp / 50 mv shunts on each battery, along with separate Xantrex Link-Pro amp-hour meters that are similar to Trimetric. In a battery bank with parallel batteries there is no way to know for sure if batteries are equally sharing the load and charging equally if using only one shunt. But most only use one shunt successfully since similar age/size/brand batteries usually share pretty well.
When we first bought our coach, we loved the two big house batteries and could dry camp better than we could with our previous smaller coach that did not have big house batteries. When we got around to installing separate shunts, like we had our previous motorhome, we were shocked to see zero amps from battery #2 when discharging or charging, probably indicating an open cell. Foretravel gave us two new MK batteries. We would not have known that only part of the bank is working without separate shunts.
But a more practical solution for Ken is to have one Trimetric that uses one shunt physically located on a junction where all house battery negative cables come together. No loads can be connected to the negative posts of all batteries before the shunt. Then buy a 3rd shunt if you want and put separate shunts on the ground of each battery, before the Trimetric shunt. Run separate twisted pair wires from these shunts to an inexpensive millivolt meter, which can be as little as a $10 cheap digital multimeter if it has millivolt scale. Also small millivolt meters can be found.
Shunts are generally not real expensive and if they are 500 amp / 50 millivolt, the millivolt directly relates to amps being drawn: 500 amps 50.0 and without decimal point, 500 amps = 500 millivolts, so one can directly read amps by looking a millivolt readout. 50 amps = 5.0 millivolts, 5 amps = .5 millivolts, etc.
Several have made this 3 or 4 shunt setup as it minimizes expensive amp-hour meters and if house bank has three batteries as lots of Foretravels have, three amp-hour meters may be a bit much. I would wait before selling extra shunt.
Some have separate shunts and use a switch to read out battery's amps, but a amp-hour meter like Timetric should be not be switched as it keeps track of amps over time, so it wants to be continuously connected to shunt.
I would use it to measure the output of the alternator. Then you will be able to see how much your working it when you leave a dry camping situation with a less than full house battery. Install it just before it feeds into the battery isolator (center post) and run a twisted pair of wires up to the dash. Install one of those millivolt meters on the dash like Barry (and Cindy) talked about. Barry Beam did this but also had several other meters as well - I remember seeing a picture of it but can find the post now.
@Barry Thanks for the info. I think I will go that route. One shunt on the common house negatives and then one shunt on each house negative connected to a millivolt meter. I found this one on ebay 3½ DC 200mV Red LED Digital Volt Voltmeter Panel Power 6 15V | eBay (http://www.ebay.com/itm/130655624019?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649) It goes to 200mv is that going to be enough? Using your formula it would max out at 200amp from each battery.
@John I like that idea. Might go that route too.
Right now I have 3 deep cycle batteries. 2 house and 1 start. I've been thinking of adding some start batteries to the engine compartment and converting the existing start to house. That would give me 3 house batteries. More power more better! :)
Edited: change 20amps to 200amps
see ya
ken
Ken, you are on a roll adding amp measuring to your 12-volt systems. You found meters that should do the trick for you.
You can also add a shunt to start batteries and alternator. Finding twisted-pair wires and running them from shunt to meter area is needed to finish the job. Dedicating a millivolt meter to a shunt, with maybe several meters stacked in one location has the advantage of seeing what is going on at the same time with just a passing glance. Switching separate shunts between one meter always means most shunts will not be displaying their current flows.
Inexpensive volt meters are a great tool, but have one disadvantage:
They cannot be powered by the same battery system being millivolt measured. I think the problem is related to a common ground point. More expensive meters have isolated power supplies. Symptoms are incorrect millivolt readout that is far from accurate. We got around the power supply conflict by using 6 or 9 volt batteries, like C, D, 9 volt alkaline dry cells to power all meters. I think there are separate inexpensive isolated power supplies that can also be used.
I've put some more thought into "!!The Ultimate Battery Monitor System!!" :) So far I'm pretty keen on have the TriMetric monitor the common ground current and installing individual shunts on each of the batteries using Barry's suggestion of milli-volt meters on the individual shunts.
What is nagging at me now is the shunts. I have these fat 3/0 cables running all through my battery compartment and now I'm going to put these skinny little shunts in the path. Won't they cause a voltage drop? How does it not cause a voltage drop? Plus using a master shunt and then individual shunts I now have 2 shunts in all of the grounds.
Looking for milli-volt meters on ebay led me to this monitor. It has an isolated power supply so eliminates the common ground problem. It comes with a 500amp shunt but it looks a little bit puny for the load they will be carrying.
DC 500A 200V Amp Volt Combo Meter Battery Monitor Charge Discharge Shunt | eBay (http://www.ebay.com/itm/DC-500A-200V-Amp-Volt-Combo-Meter-Battery-Monitor-Charge-Discharge-Shunt-/181185207121?pt=LH_DefaultDomain_0&hash=item2a2f7adb51)
I'm probably way over thinking this but what do you guys think?
see ya
ken
Yes of course there is a voltage drop, that is the purpose of the shunt, to drop the voltage across a known resistance, in this case very low resistance, will tell you how much current is flowing out of your batteries. Ohm's law E=IR ergo I=E/R. Amazed I still remember that.
Roland
Ken,
Check out this site for meters and other stuff. It all comes from China via Hong Kong I have purchased several meters from one vendor or another and they have all come in about three weeks and all have worked.
DC 200V/200A Blue+Red LED Combo Panel Volt meter/Amp meter+Shunt-in Voltage (http://www.aliexpress.com/item/DC-200V-200A-Blue-Red-LED-Combo-Panel-Volt-meter-Amp-meter-Shunt/853150858.html)
There are several vendors who sell lots, like 5 or 10, at cheaper unit prices. One on each house battery and each engine battery (6 total for me) would make a Starship Enterprise level display. Might want to have a way to hide them or shut them off at night.
Roger
Roger,
I bought a couple in the left hand column of the website. They work very well, one for house, one for engine battery. The one you feature looks even better. The only thing to watch for is buying a 12v model that uses existing 12V to power it instead of needing a 5VDC supply. They will show a problem way before you have any symptoms. Also shows me at a glance what the chassis battery voltage is while we are dry camping and on solar.
Top is house, bottom engine in photo.
Quite a few listed on ebay.
Excellent post.
Pierce
@Roger Thanks for the link. I love the translation "The power positive and cathode polarity cannot be connected crossly, or it will be damaged." :) Reading the description I doesn't mention an isolated power supply so these would probably suffer from the common ground issue that Berry mentions.
@Pierce I plan to add those meters too. My in dash monitor died and I use one mounted to my side window now. The meters make good use of the now dead space on the dash. So many projects so little time...
see ya
ken
OK, so this all sort of makes sense. Assuming I put one on the chassis battery set and one on the house battery set (or maybe one on each battery in each set)
Somg Questions...
Is a 200 amp meter big enough? I see 200A and 500A, $9 difference
The seller for the meter link I posted says it needs a separate power supply.
The meters in the ebay link show a separate 12v power connection, is this OK?
What size wiring is needed to connect to the meters?
Roger
It says it comes with a 500A shunt in the text...but then the meter itself says "0-200A". Wondr if the other 300A got "lost in the translation."
Using several dual volt & amp (millivolt) meters will give you separate amp readings for each battery, but the volt readings will all be the same, so you may rather have single millivolt meters. But you could measure volts from different places, like start battery, alternator, isolator, with the dual meters.
Stacking shunts will cause an insignificant voltage drop. I would be concerned if the puny looking shunts looks like they cannot carry 500 amps, electrically and mechanically, as ratings may be overstated.