House Battery Run Time

[charlesebrownjr]

My coach has two (2) Trace 3000 watt 12 volt inverters and six (6) 8D batteries with (2) RC7 remote control panels mounted over the windshield along with other stuff. When scrolling through various informational items contained in the displays, one display will show 25.5 hours of runtime while the other display will show just 6 hours of run time. As various appliances go on or off (refrigirator, microwave, cooktop etc) the display wii indicate various runtimes for the circuits each appliance is connected to. No problem. While at Russel coach several months ago I had Rob ck. and verify how the batteries were connected and ck there condition. I (on my own) assumed that the display showing 25.5 Hrs. runtime must have 6 batteries connected to it and the other 2 must be connected to the 2nd. display. Sounded good to me, maybe wrong! While the coach was with Xtreme Paint & Graphics having Nick Hessler go over all my CC electrical stuff, I asked him about this. Nick said that both inverters use all the batteries together. I didn' think that was correct since the displays show different runtimes. I am not far from replacing the batteries since they are approaching six (6) years of age. My thought was to add two (2) additional batteries to the inverter running the refrigirator so as to get a longer runtime for dry camping. If Nick is correct, why would CC not have kept the battery banks seperated and also why dual controls? Are alot of other coaches setup this way? Any Thoughts?

[gmcbuffalo]

Charles I have read your post three times where are the other two batteries located? I read only 6 batts.

I have 8 4D's in one bank and three inverters connected to them and all three inverters have a monitor each. The monitor are also controls for the inverters.

[truk4u]

Charles,

My RG7s are set up as the primary and slave. All functions are controlled by the primary including gen auto-start and the 2nd remote (slave) is used for a battery fuel gauge and monitoring the user selected functions. You can easily change the setup or reverse the primary and slave control. I have 5 batteries wired in parallel and my inverters are are 3000's.

Let me know when your ready for batteries.

[charlesebrownjr]

Thanks for the replys. Greg, I only have 6 batteries at this time but wii add 2 more when I replace them.

Tom I will call u win I am ready. So I assume that both inverters draw from all batteries if so, why the difference in run time? My controls seem to be as u say, a master & slave. Most of the tme I can get about 28 hrs. runtime before the Gen auto starts. Also my inverter controls do not have an AGM battery selection and shore power selection only goes to 30amps. As always, everything in my CC is working fine. I will call Xantrex about the parameters in my controls and if there might be a software upgrade to add parameters to them. Thanks guys.

[LNDYCHT]

I am not sure how your inverters are set up. In order to get run time you must have shunts ( that measures amps) on the ground side of your battery wiring to measure the draw on the batteries as well as the charge that replenishes them. In order to get an accurate number the amp hours of the batteries must be input in to the monitor. If you show a different run time on each inverter it would be reasonable to assume that there are two banks of batteries, each of which are drawn from and charged separately.

[travelite]

CharleseBrownJr, I have your identical setup in my '02 Wanderlodge LXi. Both inverters are connected to all 6 batteries, and both inverter's built-in chargers charge the battery bank. Lee's correct about the shunt. In order to get accurate battery fuel gauge information you need an external shunt - Xantrex sells a kit for this. Once the external shunt is installed, and it may already be installed, you need to go to the RC7's and alter the configuration. On the RC7 that controls the inverter that's connected to the external shunt you configure: External Shunt 'This Inverter'. You then configure the other inverter to: External Shunt 'Other Inverter'. This means only the inverter connected to the external shunt will provide accurate battery fuel gauge readout.

Each inverter has its own internal shunt on the ground terminal, but in the absence of the external shunt, each inverter will report only what it consumes; i.e., only it's local view of the world.

[charlesebrownjr]

Thanks for the help. I'll do some checking to verify my set up and my battery condition and to see if I have a shunt installed.

[mike kerley]

FWIW:

Our 93 has four 8D LifeLine batteries and they all feed the two Heart inverters. One inverter feeds outlets on one side and the other feeds the opposite side of the coach. IOTA converters charge them.

Jim Keller and I changed out our batteries last weekend after purchasing new ones from Tom at Trans Specialist (770 634 7530) at a better price than we could find anywhere else. The job was very simple with the use of a motorcycle jack to lift the batteries to the bay level, and its wheels let us roll them to and from Jim's truck. Simple job doing two at a time to minimize cable confusion. Gotta say, I saved a bunch over having them changed for me and no pain yet. Toughest part was lifting the old ones back into the truck. It helped that CC did a great job of making them very easy to get to on both buses. Much easier than changing chassis batteries.

Also, Jim's CC has two inverters with one being the primary and the second on standby until needed (load). We did not test them, but my guess is his 6 LifeLines will run that bus for many hours before the generator kicks in.

[Jon Wehrenberg]

Charles,

All the above is correct. your batteries are charged by both inverters, and both inverters draw power from them when they are not charging them.

The only thing not shared are the circuits dedicated to each inverter. Rather than frustrate yourself trying to have a gauge tell you the future (like that is going to happen), get to know your coach. You, like all of us, have "key off" loads. These are loads that are on the house batteries that we rarely think about. They are such things as the memory for our radio, clocks, the TV (even when it is off), alarm system, and any other devices that we don't see or think about. Then we have the loads we know. Lights, radio or TV, refrigerator, outlets, etc.

What you need to know is how many hours you can "dry camp" or run without recharging on your batteries. The reason your gauge cannot tell you how many hours you can go before recharging is the gauge is unlikely to know how often you open the refrigerator door, or that you just put a new case of Miller Lite in the refrigerator. It doesn't know you will have the lights on or that you will run two TVs and play a DVD on them.

After a few times you get to know just how long you can go between charges based on how you live and use electric. The time between charges is highly dependent upon the battery age and condition. The gauges probably helped a salesman sell the coach when it was new because it sounds like a great idea, but as you probably now realize the accuracy of them is based on the rate of usage at the moment you look at that feature, and not the gauge's ability to understand how you are going to use the remaining battery power.

[charlesebrownjr]

You are correct. My bus under normal living, Frig, TV & Comuter use and all the things not on but drawing power will run about 27.5 Hours before the gen kicks on. My main question was one inverter shows a run time of 25.5 Hrs. while the other show 6 Hrs. all the time. As thing go on and off like frig or aux air comp or tv the time will change at various times. ( I guess it cks every so many minutes and displays a run time) I know when there is very little draw it will show you a long run time and when under a load it will show just 6 or 8 hours. J just didn't understand why so much difference in run time if they are both drawing from all 6 batteries. Thanks for the help.

[Jon Wehrenberg]

It sounds like whoever designed or installed the gauges forgot to consider there was a second inverter drawing from the same set of batteries. Ask for a refund on that feature.

[JIM KELLER]

Charles, What Mike said might help you better understand the set up of our Buses. When reading the soft tab panels one is showing the primary inverter and the other one is reading the secondary inverter.

[Jon Wehrenberg]

How do you know which is primary or secondary? On my coach which may have the same inverters the CC has, the roles of the inverters switches. Theoretically they are supposed to be identical, but one becomes the dominant one until the batteries need a greater charge in which case they both are working, but by turning the "primary" one off for a while I can reverse their roles. This only applies to charging. When the inverters are producing 120 volt power they can only supply power to their specific circuits which are hard wired. In that case there is no dominant or primary inverter. Actually when acting as chargers (in the presence of 120 volt input to the coach) those circuits powered by inverters still go through the inverters, but only a relay so they just function as devices through which shore or generator power passes through.

[truk4u]

With my RG7's, the primary remote will show for example, absorption charge, while the secondary I use as a fuel gauge will remain on float. This seems to indicate the primary is doing the charging while the secondary (fuel gauge) is idle. Not trying to make this inverter thing more complicated, but it would be nice to completely understand the functions, which are probably different for each brand inverter/remote.

[Jon Wehrenberg]

I think which inverter tends to carry the charging load relates directly to the accuracy of its internal circuit which senses voltage and the quality of the cables and terminals which carry battery power to the inverter. Due to those variables one inverter is going to sense the need for a specific charge before the other, and once it does it will begin charging as required and the second will not read a voltage on the battery bank which indicates it needs to start charging.

If the batteries are deeply discharged I would bet both inverters will be functioning as chargers and would be in bulk or absorbtion mode. Part of what influences this may also be as subtle as if the length of cabling is longer on one run to an inverter than the other, or if the converter has separated the batteries into two separate banks for purposes of having dedicated 12 volt circuits. On my coach I have 12 and 24 volt circuits and I believe they are split into two of each. (That is a guess. I have to look to confirm.)

[mike kerley]

Charles, compare the run time indications to your computer when copying files. It will go from 30 minutes to 2 minutes back to 40 minutes time remaining in seconds. Its looking at the file its copying and guessing what size the balance of the files are which changes with every file. Much like the inverter load, it changes everytime a new load comes on or increases its draw or, turns off. I doubt a circuit could accuratly predict the "run time" for a bus. Just to many variables. Would be best to only display that feature (useless as it is) on one control panel, and leave the other one blank.

It is possible to have just one Inverter charging, then kick in the second to increase the charge rate on the same set of batteries (dc voltage/current). This is tougher to do with an ac circuit as you would have to sync the flow from the two inverters before allowing them to feed the same load, so they just split the circuits between the two inverters for ac. At least, thats my opinion.

[gmcbuffalo]

Tom with your RG7 can you choose which inverter is pri and sec by pushing buttons or is an automatic feature?

[truk4u]

Greg,

You setup the primary as "shunt, other inverter and then the secondary as "shunt, this inverter."

[Jon Wehrenberg]

Why do you want to select one over the other as primary? In inverter mode each inverter powers only its dedicated circuits. In charger mode won't either inverter work as a charger and assuming this is so won't they sort out which assumes the charging load automatically? My RH inverter now carries the bulk of the load when charging, but if the DC load ramps up the second inverter steps in and helps with the charging.

[truk4u]

It doesn't disable the functions, it merely makes one remote a gauge that you can set to continually scroll through the parameters or a single function you want to monitor such as battery voltage. The primary also controls the gen auto-start.

[Jon Wehrenberg]

OK, I understand. Different generation of inverters. Mine does not have the ability to operate Auto-start.

[BenC]

A lot of coaches have dual inverters connected to a common battery bank. A bank of 6 or 8 large house batteries (like 4D or 8D) need the added charge capacity of the second charger to minimize recharge time, even if you don't need the extra inverter capacity. Each inverter needs a remote panel for setup and configuring correctly to the battery type to which they are connected. The reason the batteries were not separated is for customer convenience. When at Vogue in the early 90's, we did about a 1 year worth of coaches with separate battery banks (one dedicated to running a refrigerator), and ended up connecting them together at a later date for longer "dry camping" time for the customers. With the batteries connected all together, creating a large single bank, the customer has the versatility and option to keep a refrigerator running a lot longer before needing to run the generator simply by turning loads off. With the bank split up into refrigerator-dedicated batteries and then "regular house batteries", the option of using all the batteries to run the fridge does not exist, even if the owner choses to reduce loads in an effort to reduce generator run time/increase the length of time between recharges. The fridge will run an average of 1/3 of each hour, regardless of if you watch television or not, use lights or not. In situations like that, the "house batteries" could be at 80% capacity, while the "refrigerator bank" is in need of a recharge. In addition, dual banks make alternator choice more restrictive (needing a regulator with "external voltage sense") since an isolator would be required. All this adds up to making the system more complex, with more parts to fail, and actually increases generator run time overall.

The Trace Engineering RV-series inverters had internal shunts between the battery negative and ground posts on the back of the inverter. When using two together, there was an External Shunt Kit available to wire up to one of the inverters. The inverter with the hardwiring of the exteral ground shunt was supposed to be set up as "External Shunt: this inverter" and would, in turn, show the "battery fuel gauge" as it was termed by Trace. The inverter without the shunt pigtail connected to it was to be set up as "External Shunt: Other Inverter" and would no longer show in the user menu the "battery fuel gauge" at all (it wouldn't be accurate anyway).
This series of inverters was unique with the shunt and "fuel gauge" feature, but it was never as accurate as hoped because to be a true indication of battery run time left, the load on the batteries and inverter would have to remain constant without any loads added or taken away. This is a difficult situation to obtain in an RV, with fridge compressor cycling on and off, water pump cycling on and off, etc, etc, etc. I had to tell a lot of customers to simply take the indication with a "grain of salt" and let your auto start feature take care of the batteries, instead of letting the gauge readings make you crazy, lol.

As far as charging and inverting, each Trace RV-series inverter operates independently. There really is no "primary" or "secondary" inverter. There are many factors that effect the dynamic in determining which one will finish a charge cycle first. The inverter that goes to float first does so because of what is "sees" as a result of battery cabling length/voltage drop, length of time at a certain "acceptance" current amount going to the batteries, and the 120vac loads it has for pass-thru (this effects if the inverter has cut back it's charge current in response to the input breaker size). All twin inverter systems will have one inverter drop to float first, then the other will finish up and eventually drop to float as well. If the inverters were installed to the optimum, the battery cable lengths, both Pos (+) cables are exactly the same length, and both Neg (-) cables are exactly the same, but all are as short as possible.

Hope this helps.

[charlesebrownjr]

Hey Ben, Thanks for the input. I understand the concepts now.

[travelite]

Whew... well that was easy, thanks Ben. :)

[JIM KELLER]

Thanks Ben, I enjoyed reading that.