# Number of 100 Ah Batteries Needed



## downplay (Sep 22, 2020)

Renogy says I must have 300+ Ah in batteries of 100 Ah batteries for
a 3000 watt inverter.

Why? Isn’t it really a matter of p=vi?

If 12v batteries each have a max continuous discharge of 100 amps,
and a 1,000 watt appliance has a max startup draw of 1,700 watts,
wouldn’t it be i = 1,700/12 = 142 amps of draw?

So, as long as I only run this one appliance, wouldn’t 2 batteries be well
within the amperage draw? 142 < 200?

Sure, I wouldn’t be maxing out my inverter, but at least I would have room
to grow when I could afford more batteries...instead of needing a whole other
inverter...


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## damoc (Jul 14, 2007)

AH amp hours is a measure of storage capacity not discharge rate and Im guessing about the reason but I have an inverter that continually trips out with over voltage with 400 ah storage but when I added that extra battery and got around 500 AH it had enough load that the charge controler could keep things in check and i no longer had the trouble.


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## damoc (Jul 14, 2007)

In vehical batteries CCA cold cranking amps is the measure of discharge rate and i think some deep cycle marine batteries will have both a CCA and a AH rating. There may also be other ways to rate a battery that I am unaware of.


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## MichaelK! (Oct 22, 2010)

If you read the specification of your batteries carefully, you will see that they publish the amphours at different discharge rates. It's very well understood that the faster you discharge a battery, the fewer amphours it will have. That 100AH rating is likely to be a 20 hour rate, which is considered standard. What that means is the highest amperage you'll get out of them for the battery to last 20 hours is 5amps. 

Most lead-acid batteries don't like being discharged at far higher levels then about 1/10C, which in your case would be 10amps. So, using one 12V battery, for good performance you shouldn't push it past 10A x 12V = 120Watts. In my opinion, Renogy is being dishonest even marketing a 12V inverter that's supposed to put out 3000W. I would bet it will never happen. You just can't pull that many amps out of a battery and expect it to have a reasonable lifespan.

With my own system, I'm running a 2000W well pump from 8am till 4pm, with some extra loads topping out at ~3500W throughout the day. But, I have a 48V system with a 400AH battery bank and a 7000W inverter. Realisticly, that's what's really necessary to actually get 3000W out of your system. I can say it because I do it! For years now!


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## Steve_S (Feb 25, 2015)

Lead-Acid based batteries can only be used to 50% DOD (Depth fo Discharge) without causing damage to the batteries. CCA and using C/20 ratings is completely moot with solar systems. NONE of this is applicable to Lithium Based Batteries.

If you have a 12V/280AH Lifepo4 battery pack, which has an operating voltage range of 10V (0% SOC) to 14.6V (100% SOC) [ SOC = State of Charge] you will get a maximum of 4.088 kWh @ 14.6V.

A Battleborn 12V/100AH Battery with built-in BMS (Battery Management System) will run between $900-$1000 USD
You can DIY for MUCH LESS, see below:

Lithium Based batteries also do not limit like Lead. a 100AH Battery Pack can actually output 100A and take 100A charging rate. Depending on the chemistry, that can triple and even quintuple.

*4Pcs 3.2V 105Ah Rechargeable Lithium Ion Battery Lifepo4 Cell For Solar System *
Total US $416.24 delivered DPP (Duty Taxes Paid) to USA.
OR
*Free Shipping to USA & 4Pcs 3.2V 280Ah Rechargeable Iron Lithium Battery Lifepo4 Battery For Electric Vehicle Solar System*
Total US $481.68 delivered DPP to USA.

Add a BMS, $100-$150. One Fuse (MRBF type) $20 and a box/casing of your choice

The Source is a Known Good Reliable Vendor which has sold us thousands of cells to our membership @ DIY Solar Power Forum 
Vendor Link: BMS,ND-3.2V-202AH,YW-3.2V-280AH direct from CN

I also regret to inform you that Renogy is the LOW Fruit of Value Gear and their support is quite sad. There are thousands of complaints about them all over the place. In fact, many of us solar folk, see someone with Renogy stuff and we won't even answer as it is too problematic. 
 
Before some shmuck runs off and tells you that Lithium Catches Fire & Explode, let me say, they are full of something..... most unpleasant. Broad Brush Generalized statements = meadow muffin.
Dangerous vs. Safe batteries, Explosion and fire test! - YouTube


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