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Old 09-28-2016, 02:18 PM   #101
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Final Design: Home Battery Bank

In the other thread, I think the original message got entirely lost on the sidebar discussion. I've finalized my design, and would appreciate if some of you could look at this and let me know your thoughts on the design.

I'm looking at powering a window A/C off of a battery bank:

KEY ASSUMPTIONS
1. window A/C will be 10k btu Frigidaire; consumes about 7.7 amps.
2. over an 8 hour period that will be about 565 ah w/12v battery bank.
3. I'm expecting to be able to run at about a 40% duty cycle, which would work out to be about 226 ah.
4. I factor in a margin of 50% more, and that gets me up to about 340 ah required over an 8 hour period.
5. I will upsize it to 600 ah of capacity just to keep things healthy.

BILL OF MATERIALS
1. 3 x Exide XMC-31 MEGACYCLE AGM-200 Sealed Maintenance Free (AGM) Marine Battery - $750
2. 1 x Xantrex Freedom 806-1840 HF 1800 Inverter/Charge - $475
3. 3 x 4 AWG Battery Cable Set - $25
4. 3 x NOCO HM318BKS Group 24-31 Snap-Top Battery Box - $50
5. 1 x Go Power! FBL-200 Class T 200 Amp Fuse with Block - $56
6. 1 x FFRE1033Q1 10,000 Btu Window-Mounted Room Air Conditioner - $300

Total Price: around $1,650 plus tax

QUESTIONS
1. Will 4 AWG be big enough to tie the batteries together? Cables are 16"
2. Any thoughts on that fuse/block combo?
3. How about the Exide batteries? Any experience with them?
4. Are any of my key assumptions off?

Thanks for your help.
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Old 09-28-2016, 04:10 PM   #102
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Quick glance but wire size looks light for the fuse size
Check the Xantrex Install Guide

Here's an excerpt: (may want to go one size larger w/ one way run > 5 ft?

Table 2 Recommended Cable and Fuse Sizes

Inverter/Charger Cable Length:Battery to Inverter (one way) Minimum Cable Size Maximum battery Fuse Size

Freedom HF 1000/1055 Less than 5 feet (1.5 meters) No. 2 AWG 150 Adc

Freedom HF 1800 Less than 5 feet (1.5 meters) No. 2/0 AWG 250 Adc
Note: Xantrex recommends not using a cable longer than 5 feet (1.5 meters) in each direction.

Cable sizes above are based on the US National Electrical Code Table 310.17 - 75C cables,
assuming an ambient temperature of 30 C cables.
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Old 09-28-2016, 04:11 PM   #103
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Here are my observations:


1. Like I said earlier I think you will be better off with a smaller A/C unit. A 5,000 btu Frigidaire draws less than 4 amps and will run at double the load factor of the 10,000 btu unit which will keep the humidity down at night.


2. Your amp hour calculations do not include inverter efficiency- about 85%.


3. #4 gauge wire will not handle 200 amps. Go with #2 gauge for a 200 watt fuse or install a 150 amp fuse. FWIW, NAPA auto parts stores will sell you the cable and crimp the lugs on for you. It won't be tinned wire, but for home use it will be fine.


4. Golf cart batteries are much cheaper than AGMs, but AGMs are ok if that is what you want.


5. You do not need a battery box for non marine use, particularly for AGMs where they are sealed so no electrolyte spills.


I would add a couple of hundred amp hours of battery capacity to your design, both for charging rate (see below) but also to provide AC to power some LED lights at night and the refrigerator. But you could just let the fridge coast at night.


That inverter should work fine, but I am a little concerned about the charger part. It is rated at 40 amps, but you rarely get the full 40 amps for long. You will need to replace 300 or more amphours while running your genset during the day. Long term cruisers typically cycle their batteries between 50 and 85% because charging the last 15% takes too long. Give it a try, but you may need to increase your battery capacity.


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Old 09-28-2016, 04:50 PM   #104
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I'm by no means an expert, but a couple of questions based on what I do know about inverters, battery banks, and AC:

1. will that inverter be able to handle the power surge when the compressor kicks on? That can be multiples of the current draw once it is running.

2. The inverter is a modfied sine wave. Will that cause issues with the compressor motor? My understanding is that many electric motors do not play well unless you have pure sine wave.

3. I agree with the comments about only having 40 AMPs on the charge side, which will only put out the full amps for a relatively short period of time, if at all.

4. Do you really think the AC will only run on a 40% duty cycle? We had some really hot, humid weather about a month ago, and the AC was running almost constantly in our 34 foot boat. this was with both 16000 and 10000 BTU marine units running (and I believe marine units are a bit more efficient as they use the water to carry away the heat, and during the day the water is usually going to be much cooler than the air.

The idea of running AC on an inverter came up quite often in the sailing forums when we had our sailboat, and I don't recally anyone finding a way to do it efficiently. Most wound up going with at least a small honda generator. We have a lot of friends who go that route with smaller powerboats and have been very pleased. Cost really isn't too much, although I don't know if a 2000 watt Honda would be able to start a 10K BTU compressor (run yes, but start is the problem). They do make soft start capacitors to deal with this issue. I won't comment about the safety issues of going this route, just pointing out that most wind up there after looking into large battery banks and inverters.
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Old 09-28-2016, 05:05 PM   #105
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Multiple small Honda gens can be ganged together, likely would need 3 to start a good sized AC.

http://powerequipment.honda.com/gene...lel-capability

The starting surge can be 10 times the running watts.

I had a small 1500 watt 300 watt surge Cobra MSW inverter and it could not start a small fridge compressor. So I took it back and got a 3000 watt - 6000 watt Peak Old WOrld Technologies MSW inverter and it easily starts everything, but will NOT start my Cruisair 16kbtu heat pump.

My recommendation, is dont even try with the Peak inverter as it blew up all its mosfets and I had to rebuilt the boards with new components, 16 mosfets, 4 mosfet drivers, 16 gate resistors, and several power output mosfets on the AC board. And I also replaced the input capacitors going from 16v to 24vdc type. So now, If I power on the inverter, I have a relay that open circuits the heatpump. Not that I would ever want to run a heatpump on an inverter. that is for my gen to handle.

My 6500 watt Onan gen easily starts my AC Heatpump, so maybe two parallel linked 3000 watt Hondas can start that AC unit.
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Old 09-28-2016, 06:40 PM   #106
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I can't find any amp-hr capacity spec for those Exide batteries. There is no way they are 200ah, which I think is what you are assuming. An 8D battery is 225 give or take, and is much bigger than a group 31. I'd guess those are closer to 100 to maybe 120 ah each. So I'd suggest checking the battery capacity real closely because I think you are off by about a factor of 2.

With a 40A charge rate, it will take around 10-12 hrs to recharge.

Is the expectation that you run off batteries at night for 8hrs, then run the generator the remaining 16hrs? If so, then recharging in the 16hrs of run time should be OK. It will also be important to your duty cycle assumptions since you will only get 40% duty cycle if the AC is running 24x7 and just maintaining temp. If you only turn the AC on at night on batteries, it will probably run at 100% duty cycle for the first 3-4 hrs.
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Old 09-28-2016, 06:40 PM   #107
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Don't skimp on batt cables and mount the inv as close to the batts as possible. Voltage drop in that loop eats quickly into your batt bank capacity.
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Old 09-28-2016, 06:52 PM   #108
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The OP is considering this battery bank and inverter/charger scheme because his Home Owner's Association does not allow running generators at night even during an extended power outage. This system is designed to cool his bedroom at night. He will run a generator for the 14 hours each day that are allowed and maybe run a bigger window unit in other rooms in the house. His generator will not run his central A/C unit.


The HOA's policy has been discussed extensively in the original thread- http://www.trawlerforum.com/forums/s...age-28288.html and obviously the OP believes it to be enforceable or at least he wants to comply, so he is thinking about the inverter solution.


As to the question of starting. The specs on the inverter he selected say that it can deliver 30 amps for 300 ms and that its short circuit supply is 55 A. That should easily start the 5K btu A/C and probably the 10K btu unit.


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Old 09-28-2016, 06:57 PM   #109
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3. #4 gauge wire will not handle 200 amps. Go with #2 gauge for a 200 watt fuse or install a 150 amp fuse. FWIW, NAPA auto parts stores will sell you the cable and crimp the lugs on for you. It won't be tinned wire, but for home use it will be fine.


Please refer to the chart below for correct wire size-it is 3/0 for 200 amps




American Wire Gauge (AWG) Cable / Conductor Sizes

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American Wire Gauge Conductor Size Table

American wire gauge (AWG) is a standardized wire gauge system for the diameters of round, solid, nonferrous, electrically conducting wire. The larger the AWG number or wire guage, the smaller the physical size of the wire. The smallest AWG size is 40 and the largest is 0000 (4/0). AWG general rules of thumb - for every 6 gauge decrease, the wire diameter doubles and for every 3 gauge decrease, the cross sectional area doubles. Note - W&M Wire Gauge, US Steel Wire Gauge and Music Wire Gauge are different systems.
American Wire Gauge (AWG) Sizes and Properties Chart / Table

Table 1 lists the AWG sizes for electrical cables / conductors. In addition to wire size, the table provides values load (current) carrying capacity, resistance and skin effects. The resistances and skin depth noted are for copper conductors. A detailed description of each conductor property is described below Table 1.
Table 1: American Wire Gauge (AWG) Cable / Conductor Sizes and Properties

AWG Diameter
[inches] Diameter
[mm]Area
[mm2]Resistance
[Ohms / 1000 ft] Resistance
[Ohms / km] Max Current
[Amperes]Max Frequency
for 100% skin depth 0000 (4/0) 0.4611.6841070.0490.16072302125 Hz000 (3/0)0.409610.40384850.06180.202704239160 Hz00 (2/0)0.36489.2659267.40.07790.255512190200 Hz0 (1/0)0.32498.2524653.50.09830.322424150250 Hz
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Old 09-28-2016, 06:59 PM   #110
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oh ,that didn't paste correctly. sorry. google American wire gauge size table as an fyi. The correct size is 3/0 for 200 amp.
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Old 09-28-2016, 08:28 PM   #111
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Another thing you should take a look at is your discharge rate relative to the battery's 20hr rating. If you drain it 50% in 8hrs, that's equivalent to a 16hr rating. At that discharge rate, the battery will have less usable capacity. Typically manufacturers will have charts that will show you the capacity at different discharge rates. In a nut shell, a 100ah battery drained at the proposed rate is probably more like an 80ah battery.
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Old 09-28-2016, 08:41 PM   #112
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I found this reference to ah capacity for various standard battery group sizes.

https://www.batterystuff.com/kb/tool...oup-sizes.html

It looks like a group 31 AGM is 125ah. So you probably need 6 of them to keep discharge to 50%.

One thing you might consider is getting the AC unit first and running it as you envision while plugged into a watt meter.

Kill A Watt Meter - Electricity Usage Monitor | P3

That will tell you what the power consumption is over a 24hr period. You could also measure just over the 8hr night period since cooling loads will probably be lower then. With the resulting info, you will know exactly how much battery capacity you need. It would be much better than guessing what the duty cycle will be. Then you can build the power system to power it.
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Old 09-28-2016, 08:42 PM   #113
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Think your math is off.

My math:
120 volts X 7.7 amps X 12 hours X 40% duty cycle / 85% inverter efficiency / 12 volts = 435 AH

Based on a 33% draw down and recharge day after day for a week or more, I'm thinking more like 1,300 AH.

As previously mentioned, AC works best at near 100% duty cycle, to dehumidify the air, which makes the room more comfortable for the same temperature. Go with the 5,000 at 80% duty cycle. Side benefit are that it's easier on your inverter (lower amps) to start the compressor, and less cycling which is more efficient.

I would size the inverter 15 second load limit to 3 times the running amps to start the compressor (120 X 7.7 X 3 = 2772 watts). You may already have that with this inverter. I would size the charger to recharge the battery in 6 hours, probably a 100 amp 4 stage charger.

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Old 09-28-2016, 09:32 PM   #114
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Thanks for this feedback. It's been extremely helpful.

- Thank you for catching the cable size issue. I'll be going with 2 AWG and will keep the length less than 5'.

- OC, thanks for the math. I corrected the math model in my spreadsheet to reflect your formula. One thing though is that I will be running for 8 hours vs. 12 hours. So re-doing what your formula is, I come up with 289.9ah for 8 hours:
AC volts = 120
amps = 7.7
hours = 8
duty cycle = 40%
inverter efficiency = 85%
DC volts = 12

"Go with 5000 at 80% duty cycle". Not sure I'm following you there. What does the 5000 represent?

- What you guys said about the sizing and output type of the inverter has me re-thinking that Xantrex. I have been looking at this one: AIMS Power PICOGLF30W12V120VR 3000 Watt 12V Pure Sine Inverter Charger



- 3000 Watt continuous pure sine power
- 9000 Watt peak power for 20 seconds
- Built in 100A smart battery charger with 7 selectable battery type settings
- Auto gen start feature
- Marine and industrial grade

- Batteries. Was thinking about the AGM batteries as I read they last longer, require less maintenance, and don't give off gases. This setup will be in my garage, so it'll be Florida hot in there as well. I would love to get some of your input on some batteries as I really don't have a good working knowledge beyond the basics on them.

- Regarding capacity and usage, I was planning on keeping the doors to the refrigerators (2) closed during the night and unplugging them. From a power draw standpoint at night, we would only be running that window A/C (although I might add in a swamp cooler for the room as well). Lighting would only be needed to get up and check on something, and I've got a couple of 18v flashlights (Ryobi One+) with a supply of 6 HC batteries.

- I would expect to be running the generator for the 16 hours or so until pole power returns. The small window A/C would run for most of the day; that way when we cut over to battery power the room would already be cooled down.

I would expect that I would be on generator power for no longer than a week. One of the nice things where I live is that we are on the same power grid as the nearby hospital. In both Charley and Wilma we were back up within 3 days.

I will be purchasing the window A/C unit and doing the test that twistedtree is suggesting.

Please keep the feedback coming. It is greatly appreciated.
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Old 09-28-2016, 09:39 PM   #115
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Quote:
Originally Posted by twistedtree View Post
I found this reference to ah capacity for various standard battery group sizes.

https://www.batterystuff.com/kb/tool...oup-sizes.html

It looks like a group 31 AGM is 125ah. So you probably need 6 of them to keep discharge to 50%.
Thanks for pointing this out. That website lists it as being 83ah, so I've got to look further into THAT one.
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Old 09-29-2016, 05:30 AM   #116
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Quote:
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...I would love to get some of your input on some batteries as I really don't have a good working knowledge beyond the basics on them.

...I might add in a swamp cooler for the room as well...
I think you're zeroing in on a good system.

Look closely at Golf Cart batteries. They're a common commodity, price is very attractive, easy to locate, easy to move around, and built for deep cycles. Also, I believe they have golf courses in Florida, so you know they can handle the environment

Swamp cooler? Isn't that just a humidifier and a fan? I'd think you'd want to DE-humidify. Or am I all wrong?

Don't sell yourself short on what you'd want to run off the inverter. Once you have it you'll find you want to plug in lots of smaller loads. Microwave, coffee maker, laptop, TV, etc. These shouldn't affect your calculations much, but do your wiring to allow some flexibility about what you can power.
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Old 09-29-2016, 05:49 AM   #117
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Red Dot and others make small DC units for big trucks if you dont need an inverter for other uses.
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Old 09-29-2016, 06:42 AM   #118
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Quote:
Originally Posted by tcpip95 View Post
In the other thread, I think the original message got entirely lost on the sidebar discussion. I've finalized my design, and would appreciate if some of you could look at this and let me know your thoughts on the design.

I'm looking at powering a window A/C off of a battery bank:

KEY ASSUMPTIONS
1. window A/C will be 10k btu Frigidaire; consumes about 7.7 amps.
2. over an 8 hour period that will be about 565 ah w/12v battery bank.
3. I'm expecting to be able to run at about a 40% duty cycle, which would work out to be about 226 ah.
4. I factor in a margin of 50% more, and that gets me up to about 340 ah required over an 8 hour period.
5. I will upsize it to 600 ah of capacity just to keep things healthy.
7.7A at 120V is going to be close to 107A at 12V DC; 7.7 X 12 = 92.4A X 1.15 = 106.26A

Of course this does not include for start up which can be as much as 2.5X the running load.

It also does not account for the Peukert effect on the bank when you discharge it at well above the 20 hour rate.

Quote:
Originally Posted by tcpip95 View Post
BILL OF MATERIALS
Quote:
Originally Posted by tcpip95 View Post
1. 3 x Exide XMC-31 MEGACYCLE AGM-200 Sealed Maintenance Free (AGM) Marine Battery - $750
2. 1 x Xantrex Freedom 806-1840 HF 1800 Inverter/Charge - $475
3. 3 x 4 AWG Battery Cable Set - $25
4. 3 x NOCO HM318BKS Group 24-31 Snap-Top Battery Box - $50
5. 1 x Go Power! FBL-200 Class T 200 Amp Fuse with Block - $56
6. 1 x FFRE1033Q1 10,000 Btu Window-Mounted Room Air Conditioner - $300

Total Price: around $1,650 plus tax
Please DO NOT buy those Exide AGM's. A general rule of thumb is that if a manufacturer can not, and will not, provide you with specifications for the battery, in ampere hours at varying rates, then walk away.

Those are NOT 200Ah batteries they are likely 100Ah batteries or even less. What is the Peukert? How many lab cycles to 50% SOC? What is the temp compensation gradient? What is the country of origin? Why no 20 hour Ah rating?

Be very, very careful with Exide's marketing material for that battery, they are comparing it to an automotive starting battery not a true deep cycle AGM or flooded product. If you want AGM there are only a hand full of premium deep cycle products out there. The premium brands are; Lifeline, Firefly, Odyssey & Northstar. The rest of the AGM's out there are wannabe deep cycle and most perform horribly in a cycling application. Trojan's new Reliant AGM is yet to be proven but could be good. The only off-shore AGM, that is of somewhat decent quality, are the Fullriver AGM's, but again these are not the quality of a Lifeline, Firefly, Northstar or Odyssey AGM battery. For this application a bank of flooded GC2's or L16's etc., with hydrocaps, would be your best value by a long shot.

I am not a fan of "high frequency" inverters as I have found them to be fairly unreliable and not just from Xantrex but also from Mastervolt too. Get yourself an old school transformer based inverter such as a Magnum and make sure it is pure sine. AC's, microwaves etc. do not like MSW.. Xantrex wants to see a minimum wire size of 2/0 and a min fuse of 250A for the HF 1800. All system wiring should ideally be the same size. Remember we need to account for in-rush/start up with inverters where they can supply up to double or more of the face value rating.

A 40A charger is far too small for a 600Ah bank. A transformer based inverter can supply double or more the charge current of a high frequency inverter.

Quote:
Originally Posted by tcpip95 View Post
QUESTIONS
Quote:
Originally Posted by tcpip95 View Post
1. Will 4 AWG be big enough to tie the batteries together? Cables are 16"
2. Any thoughts on that fuse/block combo?
3. How about the Exide batteries? Any experience with them?
4. Are any of my key assumptions off?

Thanks for your help.
4GA is too small for any inverter of that size. The fuse should be class T and 250A for that inverter, but I would not recommend that inverter.

The Exide batteries are third rate AGM's, if that. You'd be better with Deka AGM's but those are also a low-tier dual-purpose marginal cycling AGM battery. Deka's GEL battery is terrific but their AGM batteries are really quite automotive grade.

As for key assumption we can't for get Peukert. 107A on a 600Ah bank is a discharge rate that is 3.6X higher than the 20 hour discharge rate where a battery gets its Ah rating from (except Exide's (wink)). For a 100Ah battery to deliver 100Ah it can only do so at 77F and at a 5A discharge rate. For a 600Ah bank this would be a 30A discharge rate in order to deliver 600Ah's.

A discharge rate of 107A is 3.6X higher than the 20 hour rate on a 600Ah bank so your actual usable capacity will be significantly less. Using a Peukert of 1.2 with a 107A load on a 600Ah bank you would net only 465Ah's of usable capacity to 0% SOC but you can really only go to 50% so you're really only getting about 226Ah of usable capacity from a 600Ah bank at a 107A load..

If the bank has a Peukert of 1.3 you're now down to 410Ah's or 205Ah's usable....

Better batteries
Bigger charger
Bigger cables
Pure Sine transformer based inverter
Lots of Ah Capacity
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Old 09-29-2016, 07:24 AM   #119
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Thanks for pointing this out. That website lists it as being 83ah, so I've got to look further into THAT one.
Where are you seeing 83ah? I'm not seeing that.
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Old 09-29-2016, 07:53 AM   #120
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Where are you seeing 83ah? I'm not seeing that.
It was on another site that someone referred me to in one of the other posts: How to Make an Emergency Home & Mobile Battery Bank

Scroll down and you'll eventually see this:

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