Generator versus idling small diesel?

[daveb]

I didn't read the roadtrek article. If they are saying the van has 1600AH worth of batteries using 6 volt batteries, then in reality there are four 6 volt 800AH batteries on board. 2 twin battery banks hooked in parallel to produce 12v. Is that what they are saying? My god how big are those batteries? Maybe the rating is 100 hour not 20 which is the norm for deep cycle batteries?

[chromisdesigns]

Originally Posted by daveb

I didn't read the roadtrek article. If they are saying the van has 1600AH worth of batteries using 6 volt batteries, then in reality there are four 6 volt 800AH batteries on board. 2 twin battery banks hooked in parallel to produce 12v. Is that what they are saying? My god how big are those batteries? Maybe the rating is 100 hour not 20 which is the norm for deep cycle batteries?

They have 8 200 ah 6 volt batteries (which is a very common RV deep cycle size, each one weighs about 65 pounds). I am not entirely sure (have read conflicting reports how they are wired), whether in 12v series / parallel or 24 volt series / parallel. The 24v hookup would be better if they are driving everything from a big inverter, which has also been implied. It allows smaller, lighter wiring and less resistance losses. However, if some of the appliances, lighting, etc. are actually 12 volt, then I am certain the batteries would be wired in pairs, and the 4 pairs paralleled.

Their literature just multiplies the number of batteries (8) by the capacity of each one (200 amp hours), to get 1600 amp hours, without mentioning voltage. My complaint with that is that they are comparing their apples to everybody else's oranges, because RV battery capacity is commonly stated as amp hours at 12 volts, NOT 6 volts!

Their setup is 1600 AH at 6 volts, 800 AH at 12 volts, or 400 AH at 24 volts -- which are ALL the same amount of storage capacity.

Also, with any kind of lead/acid battery, the USEFUL capacity is no more than half that, to avoid killing them in short order.

Now, their lithium option, with the same 800 AH, gives much more actual useful capacity, since you can drain lithium batteries down to a few percent of total rated capacity, as long as the appropriate battery monitoring circuitry is used. Of course, it is a bit $$$$...

[daveb]

Yes 800AH total is realistic out of 8 batteries but that's still very heavy for a van. But I guess so is all my add on 4x4 equipment. Roadtrek is more of a camper that is probably lighter than my van empty. Some heavy charging sessions if they're taken to minimum. Wonder what they are doing there? I have a buddy that used eight on his 5th wheel. Almost a thousand bucks worth of batteries.

[chromisdesigns]

Originally Posted by daveb

Yes 800AH total is realistic out of 8 batteries but that's still very heavy for a van. But I guess so is all my add on 4x4 equipment. Roadtrek is more of a camper that is probably lighter than my van empty. Some heavy charging sessions if they're taken to minimum. Wonder what they are doing there? I have a buddy that used eight on his 5th wheel. Almost a thousand bucks worth of batteries.

They belt a second 200 amp alternator to the diesel for charging the house batteries, plus they have solar panels.

[Chance]

Originally Posted by chromisdesigns

They belt a second 200 amp alternator to the diesel for charging the house batteries, plus they have solar panels.

Where did you find the 200 amp alternator rating?

If correct it implies much higher than 12 Volt system voltage since their advertisement claims over 5 KW of maximum power. I'd guess it would have to be a nominal 24V system charging at around 28 Volts X 200 AMPS to get in the range of advertised system power.

[Chance]

On a flight back home last night I sat next to a long-haul trucker who often shuttles different semis across the nation, and had a chance to talk with him about some of the creature comforts of new rigs. He mentioned some are set up just like RVs with bed, microwave, fridge, etc. He mentioned a few even have showers.

I asked how they keep the cab cool at night and he said the normal way is to idle the engine. He added some have small generators and some of the very newest use batteries to run a small AC at night. The batteries get recharged once on the road in the morning.

He also mentioned that some states like Florida have some stationary ACs the trucker can connect to the rig with a hose through a window. This sounds a lot like what airports use to keep planes cool while on the ground. It's also the same concept drive-in movies of the past used to cool cars.

[chromisdesigns]

Originally Posted by Chance

Where did you find the 200 amp alternator rating?

If correct it implies much higher than 12 Volt system voltage since their advertisement claims over 5 KW of maximum power. I'd guess it would have to be a nominal 24V system charging at around 28 Volts X 200 AMPS to get in the range of advertised system power.

There was a pretty extensive thread on this RV over in the Sprinter Forum when it came out. Without going back and reading it again, I believe the 5 KW figure you quote is the inverter max output, which means that at least for short periods of time you could, for instance, run the AC and microwave at the same time. Again, IIRC, what they called the "engine mounted generator" is actually a 3 KW unit, which is a typical high-capacity auto/marine type alternator. I had one like it on my sailboat.

[chromisdesigns]

I took another look at the Roadtrek site, their description of the E-trek is now quite a bit different than when it came out. They do claim 5 KW cruising generation capacity -- either they are using a 24 volt system with dedicated alternator, or they are combining the vehicle and second alternator capacities, in which case my previous recollection of a second 200 amp 12v alternator is right. The stock vehicle alternator on Sprinters is also 200 amp.

[Chance]

Originally Posted by chromisdesigns

There was a pretty extensive thread on this RV over in the Sprinter Forum when it came out. Without going back and reading it again, I believe the 5 KW figure you quote is the inverter max output, which means that at least for short periods of time you could, for instance, run the AC and microwave at the same time. Again, IIRC, what they called the "engine mounted generator" is actually a 3 KW unit, which is a typical high-capacity auto/marine type alternator. I had one like it on my sailboat.

Directly from Roadtrek page:

•Engine Mounted Generator: The 3.0 litre Mercedes diesel engine is used as the power plant to feed the electrical system, running everything when driving or parked. At idle it feeds 3.5 KW of power. When driving, it is even more powerful and charges at 5.5 KW. The Mercedes engine will run reliably to operate the vehicle, and your generator when needed.

I found claims in other forums of knowing it is a 24 Volt system. That would support 200 AMP alternator capacity since 28 Volt charging X 200 AMPs = 5600 watts, or very close to 5.5 KW.


For what it's worth, I checked weight and prices on commonly-available RV deep cycle batteries and found that to get 800 AH at 12 Volts it would take between 500 and 600 pounds of lead acid batteries at a cost of between $1,000 and $2,000, depending on quality.

To get the same rated capacity with lithium batteries as branded by SMART, it would take about 250 to 300 pounds at a cost of roughly $10,000.

Unless the vehicle couldn't handle the extra 300 pounds of weight, it'd be hard to justify the lithium batteries. In my opinion it would be cheaper to replace the lead acid batteries more often. If taken care of they could last for years.

[carringb]

Something else I just remembered seeing at the Ford dealer:
http://www.realacpower.com/

Not cheap but you could power the neighborhood if needed. I remember SMB Qatari van video made mention of providing backup power for hospitals. I wonder if this is what they installed?