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Old 05-19-2018, 02:41 PM   #11
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Believe you started this thread looking for feedback...which (from my viewpoint) you have received with honorable intent, and viewpoints that produce reasonable consideration(s). Would also encourage you to take into account the practical knowledge this audience provides, and that many of the responses are based on "lessons learned".
If you believe you've uncovered a viable solution elsewhere, then I say "go for it"

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Old 05-19-2018, 04:12 PM   #12
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Originally Posted by udfxrookie View Post
I have a 1998 Ford E-150 with a stock 130 Amp Alternator
-Red Top Main Starting Battery

-Battery isolator
2xYellow Top Optima Batteries in parrallel

For stereo and amps:
from battery bank to 2 farad cap
1 x 1000w pioneer amps
1 x 500w pioneer amp

Proposal for Rooftop A/C:
from battery bank to 2000 watt inverter
A/C Specs: 115 v, Min Circuit Ampacity: 11, Max Circuit Ampacity: 15, 60 Hertz

Will the setup I have with the battery bank in place work?
Will it drain the ba-jesus out of the battery bank?
Should I put in a capacitor for the A/C (to cover surges, etc)?

What's the difference between Power Inverter and Power Converter?
I have a Whistler P1000AC 1000 Watt Continous/2000 Watt Peak
I can get
WFCO WF-9875 75 Amp Power Converter
whats the difference and which is better?
In general we are looking for your battery size also, Red Top And Yellow Top describe the type of battery and usage. Two yellow tops in parallel is nice information, but what I am looking for is capacity or Ah (Optima usually puts this as C20 Capacity), for the starter or in this case Red Top we are looking for CCA. If you do not have that information then the model # would let us look this up.

The largest yellow top I can find is 75 Ah so you would have a bank of 150 Ah. In general we don't like to discharge more than 50% so that would mean you have about 75 Ah of usable battery power. (and that is based off the batteries being new )

Your Ac unit uses 115 * 15 or 1725 Watts at high, and 115 * 11 or 1265 watts at low.

Will it drain your battery bank, at high (1725 watts) / 12 volts = 143.75 amps. so this would mean you could get about 20 - 25 mins running off of an inverter. Note: these are rough calculations as they don't factor in Inverter efficiency , and other anomalies of running off of batteries. Even with the alternator running you would be running off of some battery power

At low power, the ac again would be using 1265 watts or 105 amps. This would increase the run time on the battery a small amout, this of course would leave you only 25 amps left for the van, again these are rough calculations. When you came to a stop at traffic lights and such the output of the alternator would be drastically less.

I would use a voltage controlled battery separator or ACR in this usage model. This would allow the battery system to disconnect during idle, and not drop the voltage of the overall system as may happen with a diode based isolator.

The "easystart" would be a good solution for the start up surge current, but it will not help in the overall running of the system.

A power inverter converts 12 DC power into 115 volt AC power. Your Whistler P1000AC 1000 Watt Continous/2000 Watt Peak is not capable of providing the power that you would need for the specified AC unit.

A power converter specifically the "WFCO WF-9875 75 Amp Power Converter" converts 115 volt AC into DC power, this model acts as a three stage charger.

They are two different pieces of equipment.

So in general for this task, I would recommend a larger alternator, a larger inverter , 2000 watt continuous , and a larger battery bank would not hurt either.

hope this helps.


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Old 05-19-2018, 04:59 PM   #13
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Join Date: Apr 2018
Location: Clearwater, FL
Posts: 9
Here's what I got:
"Power Demand:

The average 13.5k draws about 13A in warm weather, which falls right in the middle of your min-CA and max-CA numbers that you provided. Most inverters are about 95% efficient. So, here is the demand when the compressor and fan are running in the A/C:

13A x 120V / 0.95 = 1642W

Power Generation:

Let's assume for the moment that your truck is consuming 30A to keep itself running, lights lit, accessories running, and its Red Top starting battery charged. That leaves 100A for the Yellow Top batteries behind the battery isolator that you wisely installed.

100A x 13.5V = 1350W

Power Storage:

Your two Yellow Top batteries have a C20 rating of 55Ah. The C20 rating is what one can consider the "usable" storage rating since below 10.5V, most inverters will fault and shut off their AC output.

( 55Ah x 2 ) x 12V = 1320Wh (watt-hours)

Maximum Operating Time:

Using the values above, below is the estimated amount of time you could be driving down the road with the A/C running continuously. Of course, if the A/C reaches its set point temperature and cycles off for a while, this will only extend your operating time.

1320Wh / (1642W- 1350W) = 4.5 hours, assuming the batteries start off fully charged.

So, as you can see from the above, the alternator cannot quite keep up, but the discharge rate will be reduced enough to keep the A/C running for 4.5 hours. If you increased the alternator output by about 22A @13.5V, which isn't that much, you would be at a break-even point where the batteries would not be charging or discharging"

After further discussion swapping to a 250A alternator with the easy start will sustain a long time without killing the battery bank or alternator
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Old 05-24-2018, 08:25 AM   #14
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I wish you luck. Iíve fooled around with this and I donít think it will work in practice. Perhaps it will in theory but trying to run this setup without constant problems is asking too much.

Hereís how to do it the easy way. Leave your stock charging system alone and put a generator on the rear bumper. Run the generator when you want to run the roof air. You wonít hear it behind you. Iíve done it. The roof air and road noise drown out the generator.

However, Iíve done this with two different setups and the air output was no better than the stock rear air.

Iím not trying to dissuade you. I love a challenge. Iím just wondering how much time, effort and strain on the main system is worth fooling with.
Plus, the generator way could be done in a day, then you can go enjoy it and you can also enjoy it when parked.

Hint: a small and quiet 2000 watt generator will run a Coleman Polar cub 9500 btu roof AC. Itís plenty for a van. The 13,500 standard RV roof airs are too much and draw too much power anyway.

Sent from my iPhone using Tapatalk

2010 Chevy AWD home build
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Old 05-26-2018, 09:40 PM   #15
Join Date: Oct 2012
Posts: 32
I recommend contacting

They helped me with my rig from design to equipment sales to implementation and did a great job.

I used a dedicated alternator to a lithium ion battery bank to a DC powered rooftop air conditioning.. I can run the AC whether the vehicle is running or not. How long will depend on your battery bank size.

I have a shore power connector that will charge my camper batteries as well as my starter batteries.

The system works as designed.

Good luck...
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Old 10-25-2019, 01:28 PM   #16
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Location: So Cal
Posts: 15
Roof Top A/C options.


I saw this on line and thought it might give you some "alternate ideas" for roof top A/C. :P

Personally, I think the blue color of the milk crate is sweet! (Kidding)


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converter, generator, inverter

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