Is there a need for separate engine generator?

[markopolo-ClassB]

For B vans with 1 to 4 batteries (like 100 to 400ah) do you even need a separate "engine generator"?

I'm excluding rigs with larger battery banks because they have greater off-grid capability and greater charging requirements.

For reference I'll offer this post: http://www.classbforum.com/forums/showpost.php?p=27183&postcount=6 (topic: http://www.classbforum.com/forums/showthread.php?t=3420 )

The stock 124 amp alternator in this 18 year old van powers the microwave oven while cooking meals all the while maintaining a healthy 13.9 volts under load. Appropriate sized wiring eliminating voltage drop was needed.

There's a similar result from Booster here: http://www.classbforum.com/forums/showthread.php?t=2973 using a higher amp alternator.

My thinking here is that campers won't idle the engine for hours on end to power loads like an air conditioner and would instead seek shade or a campground with an electrical hook-up. They would use the "engine generator" for large but short term duration loads like a microwave oven or hair dryer.

My wish is that this could lead to lower cost B vans if stock or modestly better alternators can do the required job. Eliminating and Onan or separate "engine generator" could trim $2,000 or $3,000 off the price but still result in a highly functional RV.

Maybe manufacturers could offer something like this or at least offer an optional wiring upgrade that would make it easy to do it later.

 

[mlts22-ClassB]

With the cost of an "engine generator", for $2200 or so, I can go for a Magnum Energy "hybrid" inverter and run that from the battery bank. Then, have a decent alternator on the batteries. The result... same functionality, but a lot less wiring. This is why with the Transit upfit, I plan to go this route, where I can have the engine's alternator on, the genset on, both, or neither (for a short time,) and run from batteries.

 

[booster]

I have been asking that to myself over and over, and as it stands right now, I would say that I don't see any real need for a separate generator unless you have huge deficits to recover all the time-like Davydd does. He uses near 4 times the AH per day that we do, so the two are not really comparable. My understanding is that some vehicles can't handle different alternators because of the ECU control of them. I think the Promaster has a 220 amp alternator, so that would be fine for most folks, if it has good idle output, and doesn't drop to much from heat like many factory units do.

There is one catch 22 in the single alternator (and separate generator too in some cases) and that is in sizing it and the wiring, along with what the batteries will accept, compared to what you need if you want to run stuff like the microwave off the engine.

Even the best alternators don't like to be run at full or close to full load very much. They run hot, which drops output and shortens life. All alternators also don't give full output at van idle, so you need to go bigger with the alternator than your actual need at idle.

I will use our case as an example. The starting point was that I wanted to be able to run the microwave without draining any battery power, with the van at idle. It pulls between 80 and 100 amps depending on the voltage it sees. To get there, when considering the very low Chevy idle speed, it took the DC Engineering 250 amp alternator.
(The stock alternator was about 20 amps short.) Our wet cell Trojans will take just over 100 amps when down to 30% SOC, so that is a good combination. Our two 4ga cables are right on the edge for 200 amps continuous, but the micro doesn't run long, and the batteries are rarely that low.

All that makes the system match really well. Enough alternator to cover what the batteries and micro would pull for a very short time, and running at 50% of less capacity the rest of the time, and the wiring is OK.

Now we are looking at a switch to AGM batteries, and more AH besides, so we will lose the nice 100 amp max that the batteries will take. I don't know yet what the maximum will be, as we have discussed a few times when the topic of "self limiting" do to high resistance in the wiring causing voltage (and thus amps) drop. At full voltage, I would think the AGMs would take all the alternator would give, and that would be a bit much for the wiring continuously. I had planned on using a 12v to 12v charger, but it adds a lot of cost, wiring, is only 120 amps, and an extra ACR is needed if we want to charge the starting battery off shore power. The Circuit Wizard calculator, says we can run 10 minutes of over 200 amps (same rating as no conduit or loom) before overheating wiring, so we will watch the amps when driving to see where it runs. If we are very high, we will just do 10 minutes runs with cooling in between until the amps drop. I may also just be able turn on the headlights to siphon off enough amps from the coach.

According to the Circuit Wizard, even 4/0 in sleeving would only be good for 240 amps continuous, so if you wanted to run continuous that is what you would need, and a 250 amp alternator would be about the max you could use, unless the output dropped on a bigger one from heat. I don't remember how big Davydd's alternator is, but he has stated 240 amps as the max he has seen, and he has 4/0, so he is maxed out.

There are a couple of ways around this if you don't have huge cables, but all have compromises.

You can watch the amps on an ammeter on the dash and shut off the separator appropriately like we plan on doing. Compromise is you need to do it.

You can use the 12v to 12v charger. Compromise is that you have extra cost, complexity and low charge rate of 120 amps

You can go to a smaller alternator to limit the maximum current. The compromise is that the alternator will be running at maximum output more of the time, and it may not be able to put out as much output at idle that you want to run things like the micro.

Of course you can put in the 4/0 cable. Compromise is that it is huge, heavy, requires big fuses and separators.

If our alternator was 200 amps instead of 250, but still had the same idle output, we would have no worries, as it would probably be capable of only 160-170 amps to the coach, by the time it got hot and ran the engine. Compromise is would work at at a higher load and run hotter and not last as long.

In Marko's question he refers to 100-400ah of batteries which will also affect the amperage to the coach. At 100ah, a single 2ga probably would be OK, at 400 we are into the 4/0 area, so that is a big factor.

 

[booster]

With the cost of an "engine generator", for $2200 or so, I can go for a Magnum Energy "hybrid" inverter and run that from the battery bank. Then, have a decent alternator on the batteries. The result... same functionality, but a lot less wiring. This is why with the Transit upfit, I plan to go this route, where I can have the engine's alternator on, the genset on, both, or neither (for a short time,) and run from batteries.

I am trying to envision when we would ever need the hybrid style inverter, and can't come up with any scenario where we would. The 30 amp shore power is always adequate for what we need, as was the generator when we had it in place.

Are you going to have the 110v wiring upsized to handle more than 30 amps out of the inverter, or are you just worried about the AC and microwave starting at the same time? Although that might trip the main breaker.

 

[gerrym51]

Beats me!

 

[Boxster1971]

Another key reason for a second alternator is using lithium batteries for your house power. Their charge voltage requirements are different enough from lead acid that a second alternators offers a lot of advantages.

 

[Davydd]

Another key reason for a second alternator is using lithium batteries for your house power. Their charge voltage requirements are different enough from lead acid that a second alternators offers a lot of advantages.

That and the fact that alternators are run by computer programs to first satisfy the engine and then any house battery. Then that satisfaction is designed for the house battery they provide as an option. I think that is why Pleasure-way has been historically adamant about not adding even a second house battery. If Promaster or Transit offers an option for a second alternator bracket for one as Sprinter does then you can bet the reason is so you can do your own thing and leave the chassis system alone.

 

[gerrym51]

if i say i am not sure!

in my zion the second alternator'engine generator' has its own pulley serpentine belt and is exclusive to my Northstar tppl agm battery. the vans alternator works just on the van system and the zion uses no battery isolator because of this.

as was pointed out to me it also means that my roof solar panels will not charge the chassis battery.

i am no electrical expert. however i have learned that tppl agm and lithium are closer than standard agm to tppl. although lithium in general are the best in many ways the tppl and lithium both charge similiarly. they can strain standard alternators and burn them out. is the tppl battery the reason roadtrek split the systems-i don't know and Roadtreks not telling.

it does make sense to split lithium charging from the van's alternator to the second alternator only. less chance of burning out the van's electrical system because high charge acceptance rate batteries be they lithium or tppl agm

 

[Davydd]

Gerry, All charging - solar, second alternator and shore power only goes to the house auxiliary batteries. At least that's what I always thought and the way all my Bs worked. The chassis battery depends on use, meaning driving. There is a solution. My auxiliary batteries Trik-L charges my chassis battery when sitting. Thus solar or shore power would do so in a roundabout way.

 

[booster]

Gerry, All charging - solar, second alternator and shore power only goes to the house auxiliary batteries. At least that's what I always thought and the way all my Bs worked. The chassis battery depends on use, meaning driving. There is a solution. My auxiliary batteries Trik-L charges my chassis battery when sitting. Thus solar or shore power would do so in a roundabout way.

This is definitely not the case with any of the units that don't have a second alternator and do have a separator instead of an isolater. Nearly all Roadtreks since the late 2000's are that way.

If you have charging level voltage on either side of the separator, it will close and all the batteries will be charged together, no matter what the source, so all will charge on the engine, the generator, solar, shore power, or your portable nuclear reactor . It is a nice feature when the van is stored, so no trickle charge needed, and it also lets the starter battery get a better charge from the shore power or solar once in a while. Many folks have been saved when their starting batteries went dead by running the generator to charge it up enough to start.

 

[gerrym51]

there is no isolator or separator in the zion with engine generator system-per jim hammill. it is not like other Roadtreks.

 

[booster]

there is no isolator or separator in the zion with engine generator system-per jim hammill. it is not like other Roadtreks.

With the engine generator option, there would be no separator. I would think that there probably is if you have the standard charging system, unless they have changed the way they do things, because you need a way to charge the coach batteries.

 

[gerrym51]

With the engine generator option, there would be no separator. I would think that there probably is if you have the standard charging system, unless they have changed the way they do things, because you need a way to charge the coach batteries.

Booster- i said with engine generator system. a zion with onan gets standard configuration.

of course you can get a zion with neither generator also

 

[booster]

And this brings us full circle back to the question that came up several times in the past.

Why no way to turn off the engine generator output to the coach batteries to prevent overcharging? Unless they have added one to the Zion?

 

[Davydd]

And this brings us full circle back to the question that came up several times in the past.

Why no way to turn off the engine generator output to the coach batteries to prevent overcharging? Unless they have added one to the Zion?

I'm no expert on this but I can observe. While driving I can see the drop in charging as the batteries reach full. They must be doing something with Advanced RVs. I can't speak for Roadtrek but I have not read a lot of discussion of it being a problem.

 

[booster]

I'm no expert on this but I can observe. While driving I can see the drop in charging as the batteries reach full. They must be doing something with Advanced RVs. I can't speak for Roadtrek but I have not read a lot of discussion of it being a problem.

You will see the current drop as the batteries fill with all battery types. It doesn't take anything special. It is the holding the voltage on the batteries once they are full that is the issue and overcharge. Your BMS is shutting off the charge, I assume, (we don't know on what parameters, though) so you avoid the damage. The systems with no way to shut off the charging are the ones that risk damage.

 

[gerrym51]

And this brings us full circle back to the question that came up several times in the past.

Why no way to turn off the engine generator output to the coach batteries to prevent overcharging? Unless they have added one to the Zion?

i have a voltage meter i put into a 12 volt outlet in the coach. when the battery is full and the engine generator is working it stays between 13.2 and 13.8. when the battery is not fully charged and it starts it jumps to 14.1 -14.4.

Jim Hammill has said this alternator has special charging controls-it adjusts to the state of battery charge. I don't claim to understand it but in generalities.

i think Balmar alternators explains this stuff

 

[booster]

I just looked at the Balmar site to see how they are doing it.

They are sampling the excitation current to determine how much output the alternator is putting out (charging current). It appears they have all externally regulated alternators, so they would use the Balmar external smart regulator, so you should see that item somewhere in the engine compartment, I would think.

It certainly is a much better system than just hooking up directly to the batteries with no controls on it, either with an engine generator or through a separator or isolator.

The only real downside is that the alternator can get fooled either by coach battery power use, or charge coming from another source like solar, so the accuracy of ending the high voltage charge can affected negatively, I would think.

If you have some power use in the coach, like the frig, charging the laptop, etc, it will tend to stay in high voltage after the batteries are full. If the solar is putting power into the batteries, the alternator will drop the voltage early (not as big a deal as staying in longer, as the solar will be finishing the battery charge).

My guess is that they have the smart regulator programmed to allow for some coach power use, so that if there is an error it is too the safer/stop early side, rather than the stay in too long side. Not extremely accurate or consistent, but a decent compromise. Having solar gives you a lot more window to stop the charging early, than if there was no solar.

If manufacturers are using systems like the smart regulated Balmars, it helps explain the high cost of engine generator setups, as the stuff is more cost than just putting a big alternator.

 

[Davydd]

You will see the current drop as the batteries fill with all battery types. It doesn't take anything special. It is the holding the voltage on the batteries once they are full that is the issue and overcharge. Your BMS is shutting off the charge, I assume, (we don't know on what parameters, though) so you avoid the damage. The systems with no way to shut off the charging are the ones that risk damage.

I guess I am confused by your question of "why no way?"

Booster: Why no way to turn off the engine generator output to the coach batteries to prevent overcharging? Unless they have added one to the Zion?

 

[avanti]

On the narrow issue of solar charging the chassis battery in the case of a second alternator:
It seems to me that a Trik-L-Start or equivalent can be used in this (or, really, any other) configuration. It bridges from the coach to the chassis systems and appears capable of stealing current from the coach to maintain the chassis battery under any scenario I can think of. Cheap and easy solution to many problems.

I run a Trik-L-Start along with a "dumb" (alternator-controlled) isolator. Seems ideal, except perhaps for the "disconnect when fully-charged" scenario, and I'm working on that.