Selecting inverter size - Ford Transit USA Forum
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post #1 of 8 (permalink) Old 03-12-2019, 03:56:PM Thread Starter
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Selecting inverter size

I am considering this device for use in a camper conversion, which will allow the use of shore power and support a large (300 watt) solar panel.

https://www.fuelzero.com/2000-6000w-...k-12v-2000.htm

Forum member @orton has mentioned that in his location his 300 watt panel handles most of his battery charging requirements; he uses a second vehicle battery powered inverter and a three stage charger to charge batteries if needed. I am trying to figure out what size vehicle powered inverter I would need to do the same with this device, and whether or not the 60 amps available through a single customer connection point would be sufficient. I would only use this inverter to charge the house batteries when required; I would not use the vehicle powered inverter for other AC loads while driving.

The specifications state that the "Charger AC Input Breaker Rating" is 30A, and tha the Maximum Charge Current is 65A. The Solar Charger has a Maximum PV Charge Current of 40A. I believe this means that the charger is capable of using up to a 40A from solar and 30A from AC, but will not output more than 65A total, even if avaible in the agreggate from solar and AC. Does this make sense? If so, I need an inverter that can provide up to 30A to the AC side. In my limited understanding, the 60A of 12V DC from the CCP would power, at most, a 700 watt inverter. If so, what, if anything, would I need to do to ensure the vehicle powered inverter did not exceed the 30A limit of the charger?
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post #2 of 8 (permalink) Old 03-12-2019, 11:07:PM
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I would recommend obtaining and thoroughly reading the installation manual before purchase. I don't see a link for it so that raises flags for me. An all-in-one unit does seem appealing but if anything goes wrong or doesn't work as intended then you have to replace the whole shebang.

30A on the AC side using an inverter is close to 400A (with losses) on the DC side. (unless you meant that you need 30A is pass through only while on shore power) That's an enormous current so you'll need a very large battery bank that is capable of handling that draw. A single Battleborn lithium battery can deliver 100A max. So you would need at least 4 of those and some monsterous cables to support that. I would consider a 'safe' DC current to be under 200A but even that requires large cables and very careful installation by a knowledgeable professional.

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post #3 of 8 (permalink) Old 03-13-2019, 02:01:PM Thread Starter
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Thanks Hein!

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I would recommend obtaining and thoroughly reading the installation manual before purchase. I don't see a link for it so that raises flags for me. An all-in-one unit does seem appealing but if anything goes wrong or doesn't work as intended then you have to replace the whole shebang.
Agreed. There is some discussion on another thread noting the similarities between this unit and one already in use (or at least, already bench tested) by forum member @Travlin . The upside of a simplified installation that I might be able to manage on my own makes the risk of going with an unknown company (that doesn't post their documentation online) potentially worth it.

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30A on the AC side using an inverter is close to 400A (with losses) on the DC side. (unless you meant that you need 30A is pass through only while on shore power) That's an enormous current so you'll need a very large battery bank that is capable of handling that draw. A single Battleborn lithium battery can deliver 100A max. So you would need at least 4 of those and some monsterous cables to support that. I would consider a 'safe' DC current to be under 200A but even that requires large cables and very careful installation by a knowledgeable professional.
Not sure I follow you. Draw on the vehicle battery/alternator would be limted by the 60A fuse on the single customer connection point. Plan is to use that CCP to power a small inverter, then feed the AC from the inverter into the Fuel Zero device, which can accept the AC and use it to charge my house battery. Specs for Fuel Zero device state that Charger AC Input Breaker Rating is 30A. I understand that to mean that it cannot accept more than 30A AC (whether from an inverter or shore power). If this is correct, I am asking for help in picking the right size inverter to supply 30A AC, and what I need to do to limit the output of that inverter so that it doesn't exceed 30A AC. Are you saying that to deliver 30A AC to the charger, the inverter will need access to over 400A DC? That doesn't sound right, but if so, then this plan is dead in the water, because the max I could pull from the 3 CCPs is ~180A DC, and that would require activiting the two now-dormant studs, an activity I am trying to avoid.

It is entirely possible that my limited knowledge has me asking the wrong question or not recognizing the enormous current that you are warning about, but I'm not following. Am I missing something?

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post #4 of 8 (permalink) Old 03-13-2019, 09:00:PM
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You're talking about converting DC to AC to supply a charger converting AC to DC. It would make sense and probably be less expensive to use a battery to battery charger such as a Sterling.

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post #5 of 8 (permalink) Old 03-13-2019, 09:41:PM Thread Starter
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Presumably because of the efficiency losses? I understand there will be some loss converting from DC->AC->DC. Goal is to charge primarily through solar, then shore power, then alternator only if required which, with a 300 watt panel, I hope to be infrequent (so ok with efficiency losses). Using a vehicle powered inverter to supply AC to a battery charger is a method popularized by Orton and adopted by other forum members, presumably because it meets their needs. The fuel zero checks a few boxes, supplying mppt charger, inverter, and charger; I had assumed the cheapest way to add alternator charging is with a small ~$100 vehicle powered nverter. Is there a $100 DC to DC charger that can be implemented as easily?

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post #6 of 8 (permalink) Old 03-13-2019, 11:08:PM
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A B2B DC to DC charger is functionally the same as a vehicle powered inverter to a shore power charger. Just in one box instead of two. The advantage of the vehicle powered inverter is the availability of 120 volt AC for other uses besides charging.

In my case I can use the power for charging or heating shower water or heating air. When switched to charging that also powers the duplex outlets in the van. I can charge my electric bike with the engine running.

Going from DC to AC and back to DC for charging is not efficient with approx. 15% eff. loss for each function. No noticeable change in fuel mileage. In my case the vehicle powered inverter is my backup method of charging. Maybe used a couple of times a year. The 300 watt solar panel is the primary method of charging the house battery.
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post #7 of 8 (permalink) Old 03-13-2019, 11:10:PM
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Are you saying that to deliver 30A AC to the charger, the inverter will need access to over 400A DC?
I was off on that. I shouldn't do math late at night.
The formula to use is Power(watts) = Volts * Amps
And applies to both AC and DC systems.

So applying that formula to what I my understanding of what you were planning...
30A x 120V = 3600 watts
3600watts / 12V DC = 300A Not 400A as I had stated.
Add in inverter losses and figure a voltage drop to perhaps 11.5 V (although your alternator might no go that low)
Then you are getting close to 350A
Which is still a lot.

But I may not have understood your question correctly in the first place. A rule of thumb is; to generate a given number of amps at 120V takes roughly 10 times that current on the DC. Again, not accounting for losses and voltage drop

Large inverters over 1000watts can pull a lot of current on the DC side regardless of the source. That can be a fire hazard due to the heat generated by insufficient or improper wiring or fusing. Batteries (or alternator) and cables must be able to handle that. And you should protect and limit that with a fuse or breaker. To limit that current from the chassis it is best to either use a small chassis side inverter as Dave does or a properly sized DC-to-DC charger.

So if you max draw from the alternator via the CCP is 60A then the chassis powered inverter shouldn't be more than 720watts at 12V. The chassis side is actually 14.1 volts so you could go up to 850 watts but then you are running very close to the max which generally isn't the best practice.

Sterling make a good DC-to-DC charger. Dave's system accomplishes the same goal and that is to limit current draw from the alternator. My only reservation is that I prefer not to have 120V live until I need it. He uses it to power other appliances while driving and has the experience to do so safely. Your are presumably a Dad with precious cargo so limiting use of 120V in a metal vehicle is for me a safer practice. There is such a thing as hot skin condition which happens more frequently than people realize and can be lethal. I'm not trying to scare you but you should read this book before wiring up an inverter in a vehicle or RV. No~Shock~Zone RV Electrical Safety It's an eye opener.

One more concern....
UL-458 for mobile inverters allows the 120V to be split between hot and neutral. That means that the neutral is not 0V. It is 60V. This is not uncommon with inexpensive inverters. These types of inverters should never be wired into a house system with outlets because it can expose the user to a neutral that isn't neutral at all. Only thing you should do is plug an appliance directly into the inverter outlet.

All the best,
Hein
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post #8 of 8 (permalink) Old 03-14-2019, 09:31:PM
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Goal is to charge primarily through solar, then shore power, then alternator only if required which, with a 300 watt panel, I hope to be infrequent
I'd suggest waiting to see how your system works before bothering with the engine powered inverter. You'll probably never need it. My system has run for around 2 years and never needed an external charge. It consists of 2 160 watt panels charging an 8D battery which supplies a fridge, lights, water pump, 12V outlets and inverter used for a toaster, electric kettle and, sometimes, the water heater. The inverter can be switched to run off the start batteries and I carry a charger. The charger has only been used to top off the start batteries when the behemoth has been parked for awhile.

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