Run AC's from Inverters or not

[davidbrady]

I've always enjoyed the ability to power cruisairs and roof airs via my Trace SW inverters powered by the engine driven alternator. My cruisairs need around 2kW of power each; the engine driven Delco Remy 50DN alternator is good for 7kW continuous. At 24V the draw is 80A per cruisair which to me doesn't appear to be a strain on the venerable 50DN. When traveling in moderate climates I'll often run up to two cruisairs off the alternator/inverters, one on each inverter. The 50DN is rated at 300A continuous duty and the inverters are known to run 7x24 for 15 years or more without failure in off-grid installations. In hot, hot weather I'll run the generator and four cruisairs but when I pull into a CG I often kill two cruisairs and turn off the generator. My inverters quickly and seamlessly transfer power over to the batteries. (Or, I can let the Vantare Power Management automatically prune two cruisairs). When I connect shore power the inverters seamlessly transfer power to shore all with nary a hiccup from the cruisairs. I enjoy the flexibility, redundancy, and seamlessness of this approach. What's your opinion on running air conditioners from the inverters?

[cmillsap]

(06-08-2017 13:01)davidbrady Wrote:  I've always enjoyed the ability to power cruisairs and roof airs via my Trace SW inverters powered by the engine driven alternator. My cruisairs need around 2kW of power each; the engine driven Delco Remy 50DN alternator is good for 7kW continuous. At 24V the draw is 80A per cruisair which to me doesn't appear to be a strain on the venerable 50DN. When traveling in moderate climates I'll often run up to two cruisairs off the alternator/inverters, one on each inverter. The 50DN is rated at 300A continuous duty and the inverters are known to run 7x24 for 15 years or more without failure in off-grid installations. In hot, hot weather I'll run the generator and four cruisairs but when I pull into a CG I often kill two cruisairs and turn off the generator. My inverters quickly and seamlessly transfer power over to the batteries. (Or, I can let the Vantare Power Management automatically prune two cruisairs). When I connect shore power the inverters seamlessly transfer power to shore all with nary a hiccup from the cruisairs. I enjoy the flexibility, redundancy, and seamlessness of this approach. What's your opinion on running air conditioners from the inverters?

David,

I often run two roof A/Cs off the inverter. The bath/bedroom unit and the salon unit are wired to run off the inverters. The Inverter DC amps display shows about a 65 to 75 amps load. The inverters will stay on bulk charge while the two air conditioners run while we are traveling even if the generator is running. Apparently, the 50 DN alternator (when running) has priority over the generator and it feeds the inverter/chargers which keeps the energy replaced in the batteries. That tells me that the 2 A/C units pull a lot of power out of the batteries and the inverter/chargers must work hard at continually bulk charging the batteries. When parked (50Dn not running) all A/C units evidently run off the generator power or shore power as the charge rate of the batteries go to float quickly.

So, it appears, at least on my bus and while traveling, that regardless of whether I run the generator or not, 2 A/C units run off the inverters. With 3 A/Cs running the generator load runs about 3 to 15 amps which is about the load required to run one A/C unit.

I'm going to ask Marathon if in fact the A/C units are wired this way when I'm there later this summer

[davidbrady]

Chuck,

That's how all four of my cruisairs are wired. All four are powered thru the inverters; in fact, all 120VAC loads are powered thru the inverters. I'm guessing if you check your inverter's amp meter it'll say -65 to -75A indicating the amperage is being directed from the inverter into the battery bank. In other words, the inverters are charging the battery bank and as you say are in Bulk charge. You should be able to pull them out of Bulk by going into the control panel and backing absorption time from 3 hours to zero. When you do this the bulk led will extinguish at which point you can restore the absorption time to its default of 3 hours. (Anytime incoming AC is switched, whether shore or genny, the inverters will go into Bulk charge and stay there for 3 hours). We know an inverter can't simultaneously charge and invert but they can simultaneously charge and send 120VAC power to your AC's from your generator using their internal transfer switch. I'm thinking that when you're traveling and your bedroom and salon AC's are on and the generator is running the inverters are charging and via their internal transfer switches they are sending generator power to the ACs - I would think this is so because of course the power coming from your 50DN is DC and the air conditioners require AC. If the inverters are charging then the AC power isn't coming from your inverters so it must be coming from the genny, but your low genny amperage load puzzles me??? Your setup is also interesting in that when you're parked the two AC's wired to your inverters are transfer switched to shore or genny power joining your other two inverters. Whew, that was a lot to say!

[CC_Guy]

Chuck,

Your inverters will not perform as inverters when good AC power is supplied from the generator or shore power with 2 exceptions. If the total AC load being drawn through the inverters is high, the inverters will augment the supplied AC source. The other exception is when the source voltage is low. In this case, the inverter will augment incoming shore power to maintain a constant AC output voltage.

Marathon is the king of transfer switches. A typical Marathon will have the following:
-- When you are on inverter power some AC loads will be shed from reaching the inverter through transfer switches.
-- When 240V is not present on shore power, a transfer switch will shed high demand, none essential loads.
-- Only 2 air conditioners can be powered through the inverters. Through a transfer switch you can select which 2 on one of the inverters while the other inverter is dedicated to the one air conditioner, if you have 4 roof airs.

[CC_Guy]

I run dash air and, if needed, one or two roof airs off the inverters. If the temperature is extreme and someone is riding in the saloon I would rarely start the generator and run all 3 roof airs.

[travelite]

Chuck,

I'd check menu item 11, "AC Inputs", on your inverters. Scroll down to "Set Gen Amps AC". CC_Guy brings up a good point. The inverters will try to augment the power provided by your generator if the generator load exceeds the configured setting in "Set Gen Amps AC" under menu item 11. Could it be that someone set this parameter artificially low, for instance, in your case to 15 amps? If so, then the inverters will supply the additional power needed to power your air conditioners, and the inverters won't let your generator supply more than 15A per leg (as seen by your inverters). In your case the inverters are powering the air conditioners on a sustained basis because the 50DN alternator is charging your batteries. It's confusing because the inverters Bulk or Float LED will be 'on' even though the inverters are not charging the batteries. If you look at your "Inverter/Charger Amps AC" meter it will read negative indicating that current is flowing from the inverter to the loads. You might try reprogramming menu 11, item "Set Gen Amps AC" to the amperage capacity of your generator, or simply set it to 60A which is the max you can set it to. This should take the load off your 50DN and put it on your generator and allow your inverters to charge via the generator.

[cmillsap]

Thanks David & CC Guy,

Trying to understand the sophisticated and complex integrated electrical circuity of a Prevost converted motorcoach is an enormous task. All owners should try to at least learn the basics.

My Gen AC input is set at 60A. The inverter menu is complex and confusing. So, I must follow the manual closely when accessing. I’ve tried to memorize the basics of the inverter menu operation but forget most of it within a few days. We’re in 50*F weather presently so I can’t run the a/c units to check inverter amp meter for negative amps loads.

All is probably normal but the inverters showing bulk charging while the 2 A/Cs are running off the inverters really is confusing. If I understand correctly, the batteries are actually being bulk charged but by the 50DN and not the inverters as I know they cannot invert and charge at the same time.

Regarding the 15 amps showing on the generator output amp meters when running 3 a/c units, it may be that the a/c units are cycling whereby all 3 of their compressors are not running at the same time. However, it’s interesting that the 2 legs are staying balanced at 15 amps. You would think that the one leg powering 2 a/c units would jump up to 30 or so amps when those 2 A/c units are cycling on. It may be happening and I’m just missing seeing it as I glance down at the display as I momentarily switch the screen to Generator. I don’t keep the Generator display on all the time as I drive with the B/U camera screen on so I can keep an eye on the towed.

When the weather gets hot I will run the generator and adjust all three of the a/c thermostats high enough to cause them all to run at the same time to see what the amp load is on each leg of the generator.

[CC_Guy]

Okay, we know your inverters are charging when the generator is running because the inverter panel is not indicating "Inverting" and the "bulk" charge light is on. BTW, the bulk charge light will stay on any time there is a power disruption of more than a few seconds. Its timer will be reset and the bulk charge will stay on for the time set in your configuration menu.

I would question your generator amp meters. With the batteries being charged and the air conditioners running your generator loads will be far more than 15A a leg.

The inverter/charger can't see the 50DN other than it's affect on the battery bank. So, if the inverter/charger shows bulk charge, the charger is producing the bulk charge. Again, this is set be the configuration menu and it is a timed event triggered every time AC power is disrupted.

If the weather is still cold and the AC units have heat pumps, try your test with the heat pumps on.

[davidbrady]

(06-13-2017 20:22)CC_Guy Wrote:  Okay, we know your inverters are charging when the generator is running because the inverter panel is not indicating "Inverting" and the "bulk" charge light is on.

I think the only way of telling is to look at the sign of the "Inverter/Charger Amps AC" meter. If negative, then the inverter is inverting even though the control panel LEDs signal Bulk or Float charging as described on page 77 of the Owners Manual:

"While the inverter is supporting the generator, the BULK or FLOAT LED Indicator will remain on even
though the inverter may not be battery charging. The INVERTER/CHARGER AMPS AC meter will indicate
the support process by displaying “negative” current flowing from the inverter to the loads. The INPUT
AMPS AC will also drop during this process while the LOAD AMPS AC remains the same".

Attached are the recommended Trace settings according to Vantare.

I'd also verify the "Set Input Lower Volt AC" parameter which is under menu heading 11. The SW uses this parameter to support the generator when it detects falling voltage. This setting and the "Set Gen amps AC" setting are the two parameters that CC_GUY referred to in post 4. One's an amperage parameter and the other a voltage parameter. Both are used to augment genny power with inverter power drawn from the battery bank.

[cmillsap]

Well now, CC Guy, running the a/c heat pumps to check the generator loading is a good idea. I probably would have never thought of that. Thanks.

David, my set up is exactly the same as yours (Vantare's) except my bulk dc volts are set at 28.4 and my float dc volts are 26.4 (24 volts) and 13.2 (12 volts). All's good, as far as I can see.

I'm thinking Marathon probably programed these settings as their default settings. If I understand correctly, each time the inverters are disconnected from the batteries, they revert back to the default settings when restarted. I've had to do a Techlink full reboot 2 or 3 times since I've owned the coach which includes a full battery disconnect and inverter shut down. Each time, the inverters return to this same set-up.