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Old 12-05-2015, 01:29 PM   #1
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Default How does Voltstart determine stopping?

A poster on the Yahoo board has a Zion on order and is getting the Voltstart to cool pets. It is not the typical application like we often hear about which would be a couple of hours of AC while the owners are off doing things. It is a traveling job application, so the pets are in the van all day, nearly every day. Lots of driving, also, though.

The Roadtrek site says the Voltstart kicks in at 11.5 volts, so the AC on a 185ah battery will probably have it on very quickly. It also states that you can get up to six 35 minute charging periods, and then you have to reset it for more.

Is this inferring that whenever the Voltstart comes on, it just runs a 35 minute cycle and goes off until it sees the 11.5 volts again? I can imagine the system having the van running an awful lot of the day in the above use pattern.

AFAIK, Roadtrek does not have any kind of battery monitor on Zions, at least on non Voltstart ones, so I don't see any way they could do anything but a straight timer.

I looked at how Magnum does their automatic generator start setup, as it is in the remote but not used for our setup, and they have it so you can set it up to start on voltage, state of charge, etc. You can also program it to shut off based on state of charge, etc. You do, however, need to have the battery monitor kit on it to do that. I am sure that is how davydd's system works, also, as he has real monitoring.

For the relatively low cost of a battery monitoring system, it just seems like it would make everything else so much easier and flexible.
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Old 12-05-2015, 02:18 PM   #2
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Advanced RV is programmable. I can set any SOC by % to auto start and I can set a number of minutes to run. If the battery fully charges before the runtime it will shut off. Also I can set a quiet time where it won't start and run. There is nothing in regard to cycles so I suppose it depends on the amount of fuel in the tank. It won't come on if fuel drops to 1/4 tank. I can also turn auto start completely off and the batteries will disconnect at 20% SOC.
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Old 12-05-2015, 02:31 PM   #3
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For their application, they would be better served just idling the engine and running the AC off the engine generator. We talking about racking up hundreds, if not thousands of hours, correct? I'd probably opt for the deisel engine too, since they are built for service like this. Relying on voltrek is just going to be problematic at this point.
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Old 12-05-2015, 02:38 PM   #4
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I have wondered about the Voltstart logic and the limits on number of starts and runtime. Since it is available on all three chassis I guess the interface to the vehicle could be the standard remote start feature using the same signal as a OEM keyfob or more likely they may use instead an aftermarket remote start module. Is there some technical basis for the limits on starts and runtime or are they selected for another reason? In any case once they start the engine based on low battery voltage, I agree that they can only continue to base the engine stop on runtime and they have chosen 35 minutes as a reasonable amount if battery recharge amp-hours. With the engine generator this would be no more than about 100 amp hours of charge at best with the 200 amp idle current of the aux alternator. So, the batteries can deplete another 100 amp hours before the next restart. Of course, the delay until the first engine start would depend on the initial battery state of charge so with full batteries it could be awhile before the first engine start. The only other factors are the average load of the AC and the cycle time of the AC which will depend on the weather.

Would a battery monitor improve the performance the system? I guess it could change the engine start/stop profile but the basic overall time the engine must operate to handle the charging would not really change.

It would be interesting to get some real world data a Zion with the standard AGM using Voltstart to see how it matches this in terms of restarts, number and timing. How long will it take to use up the limit of six restarts on a typical hot day?
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Old 12-05-2015, 02:43 PM   #5
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Originally Posted by wincrasher View Post
For their application, they would be better served just idling the engine and running the AC off the engine generator. We talking about racking up hundreds, if not thousands of hours, correct? I'd probably opt for the deisel engine too, since they are built for service like this. Relying on voltrek is just going to be problematic at this point.
That would surely work but why keep the engine running if it has recharged the batteries in parallel with powering the AC. Why not shut off the engine for awhile and run off the batteries until you need more battery recharge? That is essentially what Voltstart is doing...
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Old 12-05-2015, 02:48 PM   #6
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Advanced RV is programmable. I can set any SOC by % to auto start and I can set a number of minutes to run. If the battery fully charges before the runtime it will shut off. Also I can set a quiet time where it won't start and run. There is nothing in regard to cycles so I suppose it depends on the amount of fuel in the tank. It won't come on if fuel drops to 1/4 tank. I can also turn auto start completely off and the batteries will disconnect at 20% SOC.
Advanced RV has done it right in terms of designing a better solution than Roadtrek, not sure why Roadtrek has to rush to market with what seems like a less than ideal solution rather than take the time to design something better...
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Old 12-05-2015, 03:00 PM   #7
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I'd probably opt for the deisel engine too, since they are built for service like this.
Not clear. As I understand it (and I'm no expert), modern gas engines are more forgiving of long idle times than modern diesels, due to details of the latter's exotic emissions systems. This is the reverse of the situation in the old days, when traditional diesels could idle forever, albeit at the expense of trashing up the air.
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Old 12-05-2015, 03:15 PM   #8
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With the engine generator this would be no more than about 100 amp hours of charge at best with the 200 amp idle current of the aux alternator. So, the batteries can deplete another 100 amp hours before the next restart.
200 amps at idle may be a push, it will all depend on how they set up the pulleys to get alternator speed, and it will go down when hot also.

If the AC is running, they are not going to get the 200 either, as the AC will taking 1/2 of it. So by the time you have lowered hot output and the AC running, you probably would only recover 30 amps maybe in 35 minutes. This would make for an almost immediate restart.

If you used SOC to determine the shutoff, it would likely run the entire time the compressor of the AC was kicked in, and probably shut off fairly soon if it was off for a while.

Just like they are not great for running AC overnight, these setups may also be less than ideal for long day pet cooling. I don't think I would want my van starting a dozed times a day idling 8 hours of time.
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Old 12-05-2015, 03:35 PM   #9
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I think with such a small battery pack, you'd be starting and stopping the engine quite a bit in a day's time. That is a tremendous amount of unhealthy engine wear and fuel wasting. Not to mention emissions during the start and warmup cycle.

If you could choose a much larger battery pack, the equation would change alot. Someone considering doing this should not have anything less than the 400 ecotrek, and that is not really a lot of battery to run air conditioning.
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Old 12-05-2015, 03:39 PM   #10
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200 amps at idle may be a push, it will all depend on how they set up the pulleys to get alternator speed, and it will go down when hot also.

If the AC is running, they are not going to get the 200 either, as the AC will taking 1/2 of it. So by the time you have lowered hot output and the AC running, you probably would only recover 30 amps maybe in 35 minutes. This would make for an almost immediate restart.

If you used SOC to determine the shutoff, it would likely run the entire time the compressor of the AC was kicked in, and probably shut off fairly soon if it was off for a while.

Just like they are not great for running AC overnight, these setups may also be less than ideal for long day pet cooling. I don't think I would want my van starting a dozed times a day idling 8 hours of time.
Agree completely that the real world performance is likely to be disappointing. I picked a best case alternator charge and mentioned that the AC load needed to be factored in. I think vans with small battery capacity are not going to fare well. Jim Hammill was just asked in Facebook how the system will perform on a Zion by the woman mentioned in the start of this thread. We will see what he says...
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