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Old 04-07-2011, 02:35 PM   #1
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Inverter Connection Question

I posted this on 'another forum' and got mixed responses. What do you folks think?

I found the wiring diagram below on line and I have a question...

It shows the inverter connected directly to the batteries along with a battery charger. Is this OK to do or will the current draw of the inverter put a load on the batter charger instead of the battery?



In my case, the inverter will typically be providing approx. 100W to power two smokers. Max power would be 400W for about three minutes when each smoker is started initially. So, at peak, the DC current will be about 34A and typical about 8.5 amps. Would using a setup as shown in the drawing (with two 12V batteries for now) damage the converter/charger in my TH? If so, what would a better connection be? I am not opposed to have a separate battery just for the smokers and using an inverter/charger (that I already have), but it would be more convenient to have both batteries hooked to the TH and available in case we need them.
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Old 04-07-2011, 02:41 PM   #2
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I see no reason that these hookups will not work as shown. My inverter is tied to the Positive terminal of the battery through a 100 amp fuse and I recommend you add a fuse to your setup. Your size will depend on your maximum planned draw and inverter size.
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Old 04-08-2011, 11:40 AM   #3
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Thanks, Lou... I already have the fuse, so that's taken care of.

I guess my concern was that the smokers were starting up and the current draw was highest that the converter could end up supplying the current instead of the batteries, and that may damage the converter. Is that a possibility?
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Old 04-08-2011, 11:47 AM   #4
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I don't have an inverter (yet). But the plan is to actually use a relay in between that switches between shore (generator) power and the inverter automatically.

That way if there is external power the outlet will use that power (and thus no draw on your battery during that time). Once external power fails it automatically switches over to the inverter. A bit more expensive (15A relay is about $50) but there will be no additional load on the charger once shore power is available and the full converter power goes to recharging the battery.

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Old 04-08-2011, 12:36 PM   #5
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Wait. I am confused.

Why would you use an inverter circuit to run your smoker(s) if shore power is available? Just plug it into your shore power or generator directly.

If you are running off the inverter, because you are using your battery bank, the AC to DC converter will not be providing any DC power because there is no AC to convert.

As to the auto switch, I am not sure of the benefit. I don't think the inverter can handle all AC in your camper and even if the inverter could the battery bank could not. I would rather individually manage what runs off the inverter circuit. I currently use extension cords off the inverter sockets to manage what gets hooked up to the inverter at any given time. When I get the belly cover off this summer to install the tank probes, I plan on running Romex back to a duplex convenient to the entertainment center and to a new exterior duplex outlet to be inverter only outlets.

That way if we forget to unplug the coffee maker, it won't destroy the battery charge making a single pot of coffee.
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Old 04-08-2011, 03:13 PM   #6
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Quote:
Originally Posted by herk7769 View Post
Wait. I am confused.

Why would you use an inverter circuit to run your smoker(s) if shore power is available? Just plug it into your shore power or generator directly.

If you are running off the inverter, because you are using your battery bank, the AC to DC converter will not be providing any DC power because there is no AC to convert.
It's back-up in case the power provided by the competition fails (which happens all too often) (or the generator runs out of gas for those comps where no power is provided).

I can see two choices...

1. Have a separate battery and use in inverter/charger with an automatic transfer switch to manage that battery and power the smokers. This is fine, but I would have two separate batteries, one for the TH and one for the smokers, so the total capacity available to either would be lower. This is the easiest to implement since I have the inverter/charger/transfer switch but it is modified sine, not pure sine and I've heard of issues with RFI with these.

2. Have both batteries in parallel and connected to the TH and let the battery charger in the converter charge both batteries and have the inverter connected as well (per the above) providing power to the smokers. This way the capacity of both batteries is available to either the TH or the smokers. This would mean buying a new inverter (without the charger, but I can get an 800w pure sine wave inverter for around $150.

In either case the only things connected to the inverter would be the two smokers. If shore power fails and is not going to be restored in a timely manner I can get the generator out of the trunk and fire that up to run lights.

Hopefully that makes sense.
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Old 04-08-2011, 05:03 PM   #7
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I would go with option 2 by hooking the inverter up so that it powers the external outlets. That way you hook up your TH to external power or run the generator to provide that power. Once disconnected the relay would automatically switch over to the inverter for backup power.

That way you have power even when not in a competition and actually raise the resale value if you ever decide to upgrade the TH.

I would certainly go with a true sine wave - why spend the money only to find you should have done it anyways.....

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Old 04-08-2011, 06:20 PM   #8
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Why would a smoker need computer grade power?
It is a heating element right?

I use my outside outlets for an electric skillet, toaster, air compressor, and several other high draw items, but never would I do that on battery.

I only have a 150 amp hour bank (2 75 AH batteries) and a 34 amp draw (400 watts constant draw = 34 amps x 12 volts) is very high demand and amp hour capacity is reduced by about 50% at that discharge rate.

Wind Energy Explained: Theory ... - Google Books

See the graph on page 491. My bank would only last 2 hours.
ONE 75 AH battery would last about ONE hour.
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Old 04-08-2011, 06:49 PM   #9
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Quote:
Originally Posted by herk7769 View Post
Why would a smoker need computer grade power?
It is a heating element right?

I use my outside outlets for an electric skillet, toaster, air compressor, and several other high draw items, but never would I do that on battery.

I only have a 150 amp hour bank (2 75 AH batteries) and a 34 amp draw (400 watts constant draw = 34 amps x 12 volts) is very high demand and amp hour capacity is reduced by about 50% at that discharge rate.

Wind Energy Explained: Theory ... - Google Books

See the graph on page 491. My bank would only last 2 hours.
ONE 75 AH battery would last about ONE hour.
The smokers are computer controlled. They actually do fine on a MSW inverter, but I'm concerned about RFI on the TV and radio, but I may be worrying about nothing.

The 400W draw is for three minutes when each smoker starts up. The continuous draw for each is 50W (100W total) to power the electronics and the auger that feeds the pellets into the firebox. So, for 99% of the time the current draw is 8.5A, so two Group 24 batteries (probably the same as yours) would be enough to power the smokers for the competition (total cooking time of about 16 hours) (136 Ah).

But... My typical need is for battery backup for a short period just to bridge the power outage. If the provided power is really unreliable then I get the generator out of the truck and fire that up. If that's the case then I only need the backup if I forget to refill the generator tank (Honda 3000is Handi, about 7 hours run time at a load like this).

So, I'm back to my original question. Can I hook the inverter to the batteries at the same time as the converter while connected to shore power and not damage the converter? If not I'll keep the batteries separate and use one for the TH and one for the smokers and use my existing inverter/charger/transfer switch. Considering I don't need the inverter to provide power for extended periods I guess I'm talking myself into the latter
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Old 04-08-2011, 07:01 PM   #10
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Quote:
Originally Posted by Captain Ron View Post
The smokers are computer controlled. They actually do fine on a MSW inverter, but I'm concerned about RFI on the TV and radio, but I may be worrying about nothing.

The 400W draw is for three minutes when each smoker starts up. The continuous draw for each is 50W (100W total) to power the electronics and the auger that feeds the pellets into the firebox. So, for 99% of the time the current draw is 8.5A, so two Group 24 batteries (probably the same as yours) would be enough to power the smokers for the competition (total cooking time of about 16 hours) (136 Ah).

But... My typical need is for battery backup for a short period just to bridge the power outage. If the provided power is really unreliable then I get the generator out of the truck and fire that up. If that's the case then I only need the backup if I forget to refill the generator tank (Honda 3000is Handi, about 7 hours run time at a load like this).

So, I'm back to my original question. Can I hook the inverter to the batteries at the same time as the converter while connected to shore power and not damage the converter? If not I'll keep the batteries separate and use one for the TH and one for the smokers and use my existing inverter/charger/transfer switch. Considering I don't need the inverter to provide power for extended periods I guess I'm talking myself into the latter
It might help to visualize what you are talking about if you link the smokers.

Having said that, I see no reason why you can't have the inverter tied directly to the positive terminal without any transfer switch.

I think the reason you are going this route is the computer timer right?
If the timer quits due to power failure you won't know when the BBQ is done.

Or will you have time to unplug from the camper and plug into the inverter without hurting anything?

As you can see from the photo, my inverter is tied directly to the battery positive terminal as you indicated in your drawing. The orange plug is an extension cord and the other thing is just an adapter plugged into a place where I can easily find it.
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