Guest Automatic 5/10 Amp Charger

[Jon Wehrenberg]

Bruce,

Energy is energy is energy. If you run an AC unit from an inverter or a genset, or if it is an engine driven compressor to get the exact same level of cooling requires the same energy. The only difference is in the efficiency losses between an alternator going through an inverter, or a generator's 120VAC output going through the inverter transfer switvch for example.

Assuming your coach regulator voltage set point is what you require based on your type of batteries, I would guess the inverter set point is higher by enough of a margin to effectively tell the regulator to shut off voltage output from the alternator.

Let me answer your previous Liberty question. How does Liberty do it? First, they do not run any house AC units from an inverter. If I want to run a Cruise Air while driving, I need to start the generator.

That in turn powers the Cruise Air, but also makes the inverters chargers. If the bus engine is running the inverters sense house battery voltage, and if the alternator is maintaining a charge on house batteries the inverter charging circuit is putting out minimal charging current.

If you switch your sense wire back to the chassis batteries but try to run a couple of AC units through your inverters at 24 volts your alternator will be putting out about 130 amps just to keep the AC units running. Add in other loads such as charging the chassis batteries to make up for the bus loads like daytime running lights , or to make up for other house loads like the refrigerator and you end up pushing the limits on the alternator. The greater the loads on it the hotter it runs and heat is the enemy.

If you add a second alternator it needs to be big enough so it is not run to its capacity or its life will be shortened.

If your chassis batteries are what your alternator senses (I recommend that) your house will receive the bulk of the charge if the house voltage goes down due to depletion frm AC units. The regulator will not be shut down by a higher inverter charge rate. But don't expect to get it all or for free. If you run AC units from the inverters you send power to the ACs from the batteries but the charge current going into the batteries may not prove adequate to maintain a full charge on the house batteries while they are under such loads. The house batteries and the chassis batteries will receive charging current to some extent however.

There ain't no free lunch.

I don't understand the concept of what you call over the road air. It must be a misnomer. My understanding of over the road air is a full coach Prevost system using a large engine driven compressor with large DC evaporator and condenser motors. With that system there is no need to run anything other than the engine, and it will freeze you out if set to max. The only time I ever need to run the generator while driving is if we want to run heavy loads such as the washer, dryer, other items not on the inverter powered circuits, including cruise airs (which we don't run while driving).

[jack14r]

Jon,The newer Liberties have 3500 watt Outback inverters that will run AC units,but you are right with OTR it is not necessary to use the inverters going down the road.

[0533]

First, Jon, I want to thank you for helping, for listening and always making me think.

0533 is a one of kind bus in many ways, it was designed for an experienced 3 Marathon owner who seemed to want the very best, latest and greatest equipment in hopes of creating the better mousetrap. It is special but with a few twists.

Jon wrote: Energy is energy is energy. If you run an AC unit from an inverter or a genset, or if it is an engine driven compressor to get the exact same level of cooling requires the same energy. The only difference is in the efficiency losses between an alternator going through an inverter, or a generator's 120VAC output going through the inverter transfer switch for example.

Which is more efficient?? Does anyone know??



Jon wrote: Assuming your coach regulator voltage set point is what you require based on your type of batteries, I would guess the inverter set point is higher by enough of a margin to effectively tell the regulator to shut off voltage output from the alternator.

This is a good question, I do not know what the inverter set point is, will check. Isn't it also dependent on how quickly the house batteries use up their stored charge. Is this the set point?? If the house batteries fall below 25.5?? or something?



Jon wrote: Let me answer your previous Liberty question. How does Liberty do it? First, they do not run any house AC units from an inverter. If I want to run a Cruise Air while driving, I need to start the generator.

First: I do not have cruise air's on my bus, rather I have 2 RVAC units with 4 compressors, 2 on each side, 2 are for a low setting and 2 are for a high setting. I also have a Marathon OTR . The manual says that one can mix and match, in other words, I can operate the low settings using the inverter power while running down the road or even while sitting without the engine running (few hours). I can also even add the OTR into the mix and have both operating or use OTR alone.


Jon wrote: That in turn powers the Cruise Air, but also makes the inverters chargers. If the bus engine is running the inverters sense house battery voltage, and if the alternator is maintaining a charge on house batteries the inverter charging circuit is putting out minimal charging current.

I am a bit confused here. If your genset must be operating to run your Cruise Air's, and your inverter becomes a charger (same in my case) doesn't your genset charge the house batteries?? How could the regulator/alternator sense the house batteries if they are tied to the chassis side??



Jon Wrote: If you switch your sense wire back to the chassis batteries but try to run a couple of AC units through your inverters at 24 volts your alternator will be putting out about 130 amps just to keep the AC units running. Add in other loads such as charging the chassis batteries to make up for the bus loads like daytime running lights , or to make up for other house loads like the refrigerator and you end up pushing the limits on the alternator. The greater the loads on it the hotter it runs and heat is the enemy.

I am not sure that I am following this train of thought completely, not doubt.
If I move the regulator sense wire back over to the chassis 24V shutoff the regulator (hence the alternator) will sense the need for charge from the chassis batteries, if they do not call for a charge the alternator will not provide much output. I do not see how the alternator will be suppling much of any output to the house side (reverse of my current setup) if I were to operate my AC units in the bus on inverter power. If I did not turn on (Auto Start) the genset the house batteries would drain down eventually as the alternator could not sense a need for a charge to the house.



Jon wrote: If you add a second alternator it needs to be big enough so it is not run to its capacity or its life will be shortened.

My thought was to dedicate a smaller alternator exclusively to the chassis side with a second regulator (I think) that went to the Chassis main shutoff. I would not need the equalizer anymore and maybe the isolator ??? This way the 270AMP would be dedicated to the house side and the smaller to the chassis, might leave the old install in place (isolator and equalizer) in the event of an alternator failure???



Jon wrote: If your chassis batteries are what your alternator senses (I recommend that) your house will receive the bulk of the charge if the house voltage goes down due to depletion frm AC units. The regulator will not be shut down by a higher inverter charge rate. But don't expect to get it all or for free. If you run AC units from the inverters you send power to the ACs from the batteries but the charge current going into the batteries may not prove adequate to maintain a full charge on the house batteries while they are under such loads. The house batteries and the chassis batteries will receive charging current to some extent however.

This would be so if I transferred the sense wire from its current configuration, but I do not see a way to charge the house batteries in this scenario at any rate that could support enough of a charge to maintain AC power in the bus. The chassis batteries would not require enough of a load to offer a big enough, long enough charge for the house batteries. I would need to operate my genset as you do to use any AC in the bus (other than OTR)??


Jon wrote: There ain't no free lunch.

Come to my house Jon, I owe you that much and more.


Jon wrote: I don't understand the concept of what you call over the road air. It must be a misnomer. My understanding of over the road air is a full coach Prevost system using a large engine driven compressor with large DC evaporator and condenser motors. With that system there is no need to run anything other than the engine, and it will freeze you out if set to max. The only time I ever need to run the generator while driving is if we want to run heavy loads such as the washer, dryer, other items not on the inverter powered circuits, including cruise airs (which we don't run while driving).


0533 has 2 ways to have AC running while operating the bus without the need to operate the genset. Marathon OTR, a smaller compressor than the Prevost unit, all else the same I believe?? This unit requires a less energy from the main engine to operate and produces lots of air in the bus. But if it is really hot outside desert hot you can add up to 2 RVAC compressors on the low setting (even add just one if one side of the bus is hotter than the other) and still not require the genset. If you decide to add the second set of compressors (high) you will need to add the genset to operate all unless you are using shore power.
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[Jeff Bayley]

Warning, stupid newbie question......

What is the purpose of a "guest charger?" Just what it implies - charging other things like your car?

The purpose of a chassis battery charger like this is for when you park in South Beach and block an entire lane of traffic on a Friday night and are too smashed to move the bus when you get back from bar hoping. You've left the flashers on, you go to be with the flashers on and when you get up in the morning the chassis batteries need to be topped off in order to start the coach.

Worked great for me and not so much as a single knock on the door from a cop asking me what the hell I was doing there. Maybe he thought I was waiting for Triple A but I was starring at my eyelids.

[Jon Wehrenberg]

Bruce......please understand this. The efficiency of running a generator, or putting heavy loads on the alternator is something that requires someone with some ability to eliminate all variables except the differences between the two methods. That means you need to run the test to determine fuel consumption on a day when temperatures don't vary, the road course is exactly the same, the winds are exactly the same, etc.

You have a bus that is eating money and you seem worried about a few grams per mile of diesel fuel.

Call me when you have completed the test.

What I said poorly and you did not understand was my contention that running the A C units off the inverter puts a heavy load on the alternator. Since I have no clue what loads the A C imposes I made the assumption that using the equivalent of two Cruise or roof airs is 130 amps at the 24 volt output of the alternator. Even if the regulator sense wire is on the chassis side the alternator will be putting out juice. At least it does on my coach. My sense wire is on the chassis side, and my house is still charged.

The point I was trying to make but poorly is that I personally think running AC units off inverters (actually house batteries) begins pushing the output of the alternator. In my coach my typical inverter loads are around 5 amps at 120 Volts or 25 at 24. Add in 130 for AC units, add maybe 25 more for whatever the bus uses, add in a few efficiency losses and the alternator is beginning to approach its limits. It may be running at 75% of its rated output. Your engine is working to turn that alternator, using extra fuel. If you want to run the house AC units, crank up the generator and be good to the bus alternator. You will probably use similar amounts of fuel.

If you move the sense wire to chassis the house batteries will still get a charge. Mine does, yours should. If you wish to run the AC units, just monitor the house DC voltages and if the alternator is not putting enough of a charge into the house, running the generator is the response.

If I were to run the generator on my coach while the engine was running here is what would happen. The chassis battreries would be charged at the voltage the regulator is set to. The inverters AND the alternator driven by the engine would both be charging the house, but only the higher set point would prevail once the battery voltage reached the lower set point of the two. If my inverters are set higher, the resultant house voltage would be what they put out. If the regulator had the higher voltage that would be their ultimate voltage. Whichever is the lower voltage will be overridden by the other.

Since the regulator cannot see house voltage because it senses chassis, then it has no idea the inverter voltage may be higher. It just limits the alternator output voltage. If the inverters have a higher setting only the house is affected because the isolator stops current flow back from the house.

With respect to your concerns about house battery voltage when the house is drawing a lot of current, the alternator output will flow toward the area of greatest need. If the house voltage is less than the chassis, it will get the bulk of the charge.