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Old 09-29-2016, 06:42 AM   #118
CMS
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City: Casco Bay
Join Date: Feb 2016
Posts: 308
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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