You towing a barge for the batteries your going to need for that?

Your Amp numbers are for 120 volts... not 12 volts.

 

By my math, I should get almost an hour and a half. Thats all I need....

But yes, your right. I did, and meant to quote you 120volts... I measured right from the panel. These are without the loss to the panel from the power source.

 

My point was you are not considering how many Amps you need the 12 volt battery to output for it to deliver the Amps you need at 120 volts. You don't have enough juice in your battery to even start the AC unit...

 

Im looking at a true sine, 2000 watt cont. 5000 watt peak.

Thats 41.6 amps peak @ 120v ac
16.6 amps cont. @ 120v ac

Whats the issue? That would mean,using 70+ amps an hour for full Air. It would cycle quite a bit. Maybe lowering that 10-15% of total usage. 315 amp @12v avaliable. Half is 157.amps@12v...

 

I'm not real good with electricity stuff... I'll admit that... especially the conversions between AC and DC and when you have to use RMS of the voltage etc etc..

BUT..

Amps * Volts = Watts

If you are running 30 Amps for an AC system at startup at 120 volts, that's 3600 Watts. Put that 3600 Watts on a 12 volt circuit (i.e. a battery driving an inverter with no loss) and you need 300 Amps... Not the 30 Amps you assumed. Throw in some loss due to the inverter and you are probably talking 350 Amps needed from the battery. AND... batteries are such lovely creatures that as try and suck all this juice out of it, the voltage will drop thereby needing more Amps causing the voltage to drop more etc etc... battery catches fire... air conditioner doesn't start.

Basically, you need to add a "0" to your amp requirements when going from 120v to 12v... it's 10x.. one of them laws of physics things. Now if you had a Tiara...

Now someone will pipe in and say I didn't convert something to AC from DC or some other nonsense... but the concept is right.

 

From my research Gary that sounds right. First and foremost let's say all you wanted to run was the AC. A golf cart battery typically has a 250-350 AMP/HR capacity.
That'll get that AC running for 1 HR and completely drain your batt.
You really want your bank twice the size of what you want to use....hence the barge.
Also, most decent inverters have a 15A output limit. You obviously found a bigger one than I've been eyeing but that will draw more from your Batt Bank and generate more heat and fires aren't good.
Here's some reading

 

Actually, I think a golf cart batter is usually 6 volts isn't it? That means even a 350 Ah golf cart battery won't start his air conditioner unit... Trying to suck that much juice out of a battery that fast and for any length of time is going to cause serious heat... just go drop a screw driver across the terminals.

 

Yes they are. So 2 in series let's say making his AMP/HR requirements would get him and hour, then be completely drained. Now twice the space/weight needed.

I want an inverter too, but won't run AC. Mayve the Micro for very limited use. It's low on my priority list and more than likely a project for next year.

 

The deal breaker is that you have to calculate that you only have use of half of the listed reserve for your batteries. Not a good idea to drain your batteries too much below half their capacity. Given that, you'll need twice the number of batteries that you are estimating. You'll need quite a bit of real estate to park your batteries. They need to be parked very close to the inverter for minimum loss to resistance in the cables. I don't know if you have that logistically considering you have a genset on the 280. I don't have a genset and have the ability to put 6 golf cart batteries on that pad. My dilemma is that precious real estate is very useful for essential tools and containers. So my solution is a 2000W inverter and 2 golf cart batteries. Not going to run the AC, but can run the lights, DVD, fridge, etc until the cows come home without a worry about the batteries.

 

I never assumed it was 30amps DC...
After the startup, the load would be 7.75 amps @120VAC. This converts to about 70amp hrs @12VDC.
At startup for less then a second, it would draw 28-30Amps @120VAC. Which would convert to 280-300amps @ 12VDC(for a second)
I am even thinking a capacitor could help. Like the ones for stereo amps...
I still dont see where I'm coming up short...
After starting, 70amp hrs DC, I would have 1.5 hours of half life on just two bats. Leaving one for startup untouched.

 

Another consideration is the efficiency loss of the inverter. I seem to recall it to generally being somewhere around 10-20%. Two 6V golf cart batteries in series will get you ~61 min reserve at 75A draw at 50% of their capacity. That's not considering the efficiency loss at the inverter.
http://www.interstatebatteries.com/www_2001/content/products/product_marine.asp

 

What kind of battery bank do you anticipate to use and what inverter?

 

Again, I have three group 31 105 amp wet cell bats.

I wouldnt want to have to tie all three together, so I would like to just make two work. If thats an hour, Great! If thats less than 40 minutes, Im not sure I would spend the extra cash to get a pure wave inverter. I only need it for the microwave/tv....

105*2 =210

105amp hours till both are at half. 70-80amps being pulled at running, leaves me with 1.5 hours. Am I close?

 

So...

They basically make these things already. I've looked at tying in the 2 D batteries I have for the bow thrusters into an inverter to run my fridge and freezer (two separate units). The inverter I liked was the Xantrex Freedom 30 which did 3000 watts continuous and 9000 watts peak/surge. It also has some nice features of low voltage cut off so you don't melt the batteries down. These things cost over $1000 (street price).

I just bought 4 new 8D Deka AGM batteries and here is the spec sheet:

http://www.eastpenn-deka.com/assets/base/0194.pdf

Note they have the amount of time there battery line will run at 75 Amps (and 50, etc. etc.). Now with a big honkin' 8D battery, you get about 2 hours at 75 Amps.

So I don't know... Do your own math... Here's a place Xantrex has that will calculate it for you:

http://www.xantrex.com/support/howlong.asp

If I plug in your numbers of 105 Ah for the battery (which is what they have on the chart on that calculator BTW), I can't put in 2000 watts of power. I can put in 1600 watts and get about 20 minutes (.32 hours). My gut tells me it won't start the AC unit with the smaller battery... But prove me wrong and report back!

 

I can't put in 2000 watts of power.

I would only be drawing 930 watts AC after it started.
3600 Watts AC for starting.

7.75*120=930
30*120= 3600 (for a second)

When I plug in 930 (without losses) into your web site it gives me 1.12 hours. I might be happy with that... I would perfer longer, and may add one more bat. to get me there... like I said. My goal would be 3-4 hours tops. 1-2 is good... less than 1 would be the breaking point I think.

I WILL be getting a larger inverter, so if anyone can answer my first post regarding the affects of Modified sine on a microwave please do...

 

So if I plug in 210 Ah (105 x 2) into the Xantrex calculator and stick in 2000 watts, that gives 0.52 hours (30 minutes).

I assume they are accounting for the degradation of the voltage as time goes on. If you are draining the battery that fast, I bet the voltage drops fast... Those Ah ratings are typically for a 20 hour drain I believe. Something faster than that is going to be a different rating.

 

You have a Genny and want an inverter? I'll buy you 20 batteries if i can have your genny.

 

You talking to me? You have diesel tanks?

I looked at doing an inverter due to being at anchor and turning the genny off... but at the end of the day, I don't think it's worth the hassle... I just run the genny all night... all day.... all night.... The Onan diesel genny I have is a low RPM thing and it'll go a looooong time.

 

No, I don't want a diesel genny, I want Beachcomber's genny.

 

unless you want to give me your genny and i'll sell it and buy a gas one.

 

let me clarify goals...

1. Make popcorn without starting the genny

2. I want to keep the Air conditioning running during-

A. Kids napping for 1-3 hours with genny off (CO risks, as well as I love to listen to the wind)

B. Eating out back with having the genny off (noise, small odors)

C. To watch movies without the genny on. (CO, noise,)

 

is there enough room in your ER to put more batteries with the gen in there too?

 

Yes, and if adding one battery gave me what I needed, I would maybe go that route...

 

I don't comment on these inverter threads, normally. Actually, I hate these inverter threads. Too much oversimplification and really far too much cramming 10 pounds into 5 pound bags. I'm breaking my rule so that someone does not think I have him on my ignore list.

P = I R only works for resistive loads and DC. That means that you can measure power used in watts for resistive loads only on AC systems. For inductive loads, like motors, switching power supplies and the like, you need to use VA (volt amps) and factor into the equation a power factor. We don't worry about PF on DC motors because inductance is not a factor on DC systems.

AC voltage varies along a sine wave. When you light an incandescent bulb with AC power, the current follows the voltage exactly. Not so when you put an inductive load on the AC mains. Then the current trails the voltage. Power factor is the correction used to calculate the current draw over time. Google "power factor" if you want more info. I'm not an AC power systems guy. I just know a little bit from data center UPS and backup generator work I did for some disaster recovery planning.

You're greatly oversimplifying by using watts for your microwave and air conditioner. Need to use VA. Also, remember that watts, amps and volts on AC are RMS. Peak is RMS times the square root of two. Powering big loads like air conditioning and a microwave is why the generator is there.

Best regards,
Frank C

 

I think I'll follow Frank's rule on inverter threads from now on. Now I remember why I hated my EE classes. Everytime time I got a test back, I had red on it with notes of "need to use RMS blah blah blah volt amps blah blah blah"... Bastards

I'll go back to my "gut feel" comment though. That usually works for me. My 8D batteries never last as long as they do "on paper."

 

Beachcombersc,

I understand where you are coming from. I also like those quiet times on the hook with no genset running. I also like to leave my boat anchored for a day or evening ashore without the generator running unattended. To accomplish this I added an inverter that is powered off my 24vdc bow thruster bank.

I never contemplated running the HVAC off the inverter - actually I don't even run the TV. It is only there to keep the 120VAC fridge and freezers running and to allow us to brew coffee in the morning. With this minimal load, and 2x8Ds, I can run 10-12 hours and re-charge in about 4. The reason that I opted not to run the HVAC off the inverter is that the battery weight would have been too much - and this is on a 58' boat! Also, the re-charge time gets to be ridiculuos.

Maybe you should consider skipping the AC and buy a couple of 12v fans. Even running the boats AC system in fan only mode would be possible. I realize you are in a hotter climate than me, but an open hatch and a gentle breeze from a fan can make for good napping conditions anywhere.

 

Thank you all for your opinions and time with this thread. I do value all your wisdom, or I wouldnt have asked.

I do believe I have given the specs/draw of amps in VA. I checked it running/starting on shore power the amp draw/peak with an inductive meter around the hot leg coming into the breaker panel. When the AC aif fan comes on, it starts lower, then the comp snaps on it swings the VA to 28. I did see a 30 draw once, so I quoted that number to simplify math and not skimp on load measurments.

I do and dont understand any"resistance" about talk of inverters. There are many risks even using my genny.

 

I don't think there is any resistance to inverters. Heck... I looked into them and go back and forth myself for the reasons Jeff mentioned. When you get to bigger boats, everything is run off of 240/120 volts all the time so as soon as you unplug from shore power, you have to have the generator running or everything will go bad in the fridge/freezer (ice melts, water goes everywhere, etc etc). I understand the desire as I'm always thinking I scare the fish away when we are drift fishing because the darn generator is running. Plus, I have these 2 x 8D batteries hooked up in a 24 volt configuration to the bow thruster that don't do much else. The only question I have is running the AC. In sizing the generator for my house, I went through this with the electrician because I wanted to run one of my HVAC systems (granted it was a 6 ton unit) and the size of the generator required to do that was HUGE compared to just running the fridge and lights.... so that's why I really question if it is possible to do with a battery or two (or three or four). For just running the Tv, and lights for a few hours, an inverter seems like a great way to go over a stinky genny.

I seriously want you to try to see if it works... report back.

 

You know, that's one thing I never thought about with having a bigger boat, that everything runs off AC. I can imagine that running a gen ALL of the time would get tiring.