Generator versus idling small diesel?

[Chance]

Does Sportsmobile offer anything similar to Roadtrek’s E-trek package? I ran across this system while doing research. I sounds very similar to the engine-driven 5KW Auragen generator system E350 described on first page of this thread.

http://www.roadtrek.com/etrek.aspx

The main components seem to be an engine-driven generator that puts out 3.5 KW at idle and 5.0 KW while driving, a large 5 KW inverter, and eight 6-Volt AGM batteries with a capacity of 1600 Amp-hours. Apparently the 8 AGM batteries can be replaced with two lithium batteries with a capacity of 800 Amp-hours for a weight savings of 380 pounds and faster charging time. I will guess that the lithium batteries are 12 Volt so both options have the same 9600 watt-hours of capacity.

That should be enough stored energy to keep a small AC running overnight provided batteries are fully charged. The E-trek package also includes a 245-watt solar panel but that’s probably only good for lighting and maybe small TV if engine is not idled occasionally.

As lithium batteries come down in price these kinds of hybrid charging systems may replace traditional generator systems altogether. Total costs seem to be similar if compared to diesel generator, solar panel, and 2 KW inverter. Still very expensive compared to portable Honda generator but I guess they are not exactly the same. Weight is also on the high side with AGM batteries but with lithium batteries I’d expect it to be similar to diesel generator.

[E350]

May be of interest:

http://www.ford-trucks.com/forums/99590 ... -door.html

[chromisdesigns]

The AH capacity quoted by Roadtrek is very misleading -- they use 8x200 AH 6 volt batteries. That's only 800 AH at 12v, not 1600. Apparently the ad writers didn't talk to the tech people. And, of course, you can only use, at most, about 50% of that capacity without killing the batteries in short order.

On another forum, it was posted that the lithium option has been discontinued. Not sure if that is accurate, or not. The big advantage of lithium, of course, is that it IS 800 AH of capacity, and nearly all that can be effectively used, unlike with lead-acid cells. Downside is the huge cost.

Also, their ad copy is wildly optimistic about how long you can run air conditioning from the batteries.

[Chance]

Originally Posted by E350

May be of interest:

http://www.ford-trucks.com/forums/99590 ... -door.html

I like that idea; and actually considered doing exactly the same by installing the AC though lower part of door below window. However, two things changed my mind. First, I have a cabinet on driver side that would block air flow some. Maybe I could have found a small AC with discharge mostly towards center of van or could have reduced size of cabinet. With mine the AC is also completely hidden.

I also mounted the spare tire on the driver-side rear door by building a tire carrier on the inside of the door. An AC in that location would have required an external spare-tire-carrier.

It's a cool idea though. I like it much better than putting through a rear window.

[Chance]

Originally Posted by chromisdesigns

The AH capacity quoted by Roadtrek is very misleading -- they use 8x200 AH 6 volt batteries. That's only 800 AH at 12v, not 1600. Apparently the ad writers didn't talk to the tech people. And, of course, you can only use, at most, about 50% of that capacity without killing the batteries in short order.

On another forum, it was posted that the lithium option has been discontinued. Not sure if that is accurate, or not. The big advantage of lithium, of course, is that it IS 800 AH of capacity, and nearly all that can be effectively used, unlike with lead-acid cells. Downside is the huge cost.

Also, their ad copy is wildly optimistic about how long you can run air conditioning from the batteries.

I don't know why it's that misleading since they are stating AMP X HOURS. AH is not a measure of real "energy" capacity unless the voltage is also listed. And they did that so it's not like they are either saying something wrong or intentionally misleading anyone. It's mostly that we have gotten spoiled mostly thinking in terms of 12 Volts because that's what is common in automobiles.

If one is interested in comparing energy capacity of a battery pack (like they do on hybrid cars today since they are at different voltages) the easiest way to keep things simple is to look at the capacity in watt-hours, or kilowatt-hours if of enough size. In both cases the Roadtrek seems to convert to 9600 watt-hours.

Regarding run time: If we can only get 50 percent of the energy out of battery bank, that's roughly 4800 watt-hours. And if a small window-type AC uses 480 watts, it would then be able to run 10 hours. With maybe 80 percent inverter efficiency a more realistic 8 hours of actual "continous" use from 100% to 50% batteries. A large roof-mount AC would go through batteries in a hurry.

Personally I just can't get over the weight of 8 batteries that size. It's too bad lithium RV-type batteries are so expensive.

[86Scotty]

Originally Posted by E350

May be of interest:

http://www.ford-trucks.com/forums/99590 ... -door.html

I was going to link that too. This is exactly my planned setup.

[chromisdesigns]

Originally Posted by Chance

I don't know why it's that misleading since they are stating AMP X HOURS. AH is not a measure of real "energy" capacity unless the voltage is also listed. And they did that so it's not like they are either saying something wrong or intentionally misleading anyone. It's mostly that we have gotten spoiled mostly thinking in terms of 12 Volts because that's what is common in automobiles.

It's misleading because no rv appliances run on 6 volts, so stating the AH capacity at SIX volts is akin to the old audio amplifier power wars, where you could buy a "300" watt amp that actually could only deliver 300 watts for a few seconds (so-called peak power), instead of indefinitely. Since RV and battery vendors nearly always quote AH at a particular voltage, to leave out the voltage (as they do in their ad copy) is very misleading. You read their ad and think "that's a lot of power" when it really is only half of what it appears to be. And the useable capacity is half of that, at best. Of course, nobody else points out real useable capacity of lead-acid batteries, either -- but they should!

[Chance]

Originally Posted by chromisdesigns

It's misleading because no rv appliances run on 6 volts, so stating the AH capacity at SIX volts is akin to the old audio amplifier power wars, where you could buy a "300" watt amp that actually could only deliver 300 watts for a few seconds (so-called peak power), instead of indefinitely. Since RV and battery vendors nearly always quote AH at a particular voltage, to leave out the voltage (as they do in their ad copy) is very misleading. You read their ad and think "that's a lot of power" when it really is only half of what it appears to be. And the useable capacity is half of that, at best. Of course, nobody else points out real useable capacity of lead-acid batteries, either -- but they should!

I understand your concerns but don't see a way around it. It would be more than misleading if they cut the AMP X HOURS in half just because it's at 6 Volts instead of at 12 Volts. A-H are just A-H and nothing more; and therefore can't be rerated because of differences in battery voltage. They could try to explain it as "equivalents" but that would be really confusing in my opinion. Besides, not everyone is buying batteries to connect them at/for 12 Volts. For all battery makers know buyers could be using them on a 24 Volt RV or a 48 Volt golf cart. Batteries are rated a certain way by industry standard and it would be wrong for Roadtrek to change the rating. I hate to say it, but the rating is what it is. It's up to us to know the difference.

[daveb]

The dictionary says "An ampere hour is the amount of energy charge in a battery that will allow one ampere of current to flow for one hour". AH's can be deceiving in a few ways. Some manufactures use different discharge times or different amp draws. The 20 hour rate is common but some manufactures use an 8 hour rate or even a 100 hour rate. Also different batteries have a cutoff point where the amp draw should stop to prevent damage to the battery which is not factored in. Super high amp flow can also affect the reserve capacity and contradict what the AH rating is because the rating was done at a lower draw. Just the construction of the battery is a huge factor that the amp hour rating doesn't address.
Battery voltage doesn't change the AH rating either. Two 100AH six volt batteries in series produce a single 100AH 12 volt battery bank.

[chromisdesigns]

Originally Posted by daveb

Battery voltage doesn't change the AH rating either. Two 100AH six volt batteries in series produce a single 100AH 12 volt battery bank.

This was exactly the point I was trying to make. Roadtrek says their "E" model has "1600 AH" of battery capacity...and it does, AT SIX VOLTS. This is precisely the same amount of energy storage as 800 AH capacity at 12 volts. And when someone in the automotive, solar, RV, or marine world talks about AH capacity, unless they specifically state some other voltage, everybody understands them to mean "at 12 volts"; because that is the standard voltage for these applications, unless otherwise stated.

The average RV or car guy reading the Roadtrek brochure is very likely to get the impression that they have twice as much storage as is actually there. It's deceptive advertising, whether or not it was deliberate or accidental.