how do determine what size wire to use off a 24 volt battery

Are you putting together a battery bank for an alternative energy organization? Or just wondering what gauge wire to connect 12 volt batteries?

Perchance you're trying to make up one's mind the right size of interconnecting cables betwixt the batteries themselves and the charger / inverter.

How big should the cables exist? What size? More accurately, what gauge (AWG)?

Read on… or become straight to the chart (AWG gauge versus Amps) at bottom of page.

The brusk answer (regardless of your application) is to know the maximum potential current (Amps) that will flow through the interconnecting circuit – based on your schematic. Therefore, there'due south no quick and correct respond. It depends…

I recommend getting yourself a clamp meter that measures DC current! This will help verify what's actually going through your cables! The post-obit multi-meter clench meter volition mensurate up to 400 Amps.

Klein Tools Digital Clamp Meter
(view on amzn)

The Battery Bank

A bombardment bank for an Off-Grid solar powered alternative free energy system volition consist of a number of batteries and their interconnecting terminal cables.

The batteries will be connected together in various series-parallel configurations depending on your schematic design to achieve a desired voltage and capacity to work all-time with the inverter (and charger).

The batteries volition serve equally a energy storage heart to evangelize power during periods when the solar panels themselves are either in the nighttime or under-delivering due to weather conditions.

I'one thousand not going to get into recommendations for serial-parallel battery wiring (another article). However I will cite my own current configuration every bit an example:

My Organization as an instance…

All 24 batteries are 12 volt 100 AH rated. There are 6 series strings (of four each) that are all connected in parallel to incorporate a bombardment banking concern of 48 volts @ 600 AH. That'due south a full capacity of 28.eight KwH, although 14.four KwH is safely usable (fifty% max). That said, my rule of thumb is to avoid draining more than than 30% off the top for pb acid batteries…then that gives me simply well-nigh x KwH to play with.

[ Read: How To Calculate Ah (Amp Hours) and Wh (Watt hours) Of A Battery Bank ]

This, combined with almost iv,000 watts of PV panels has been plenty to supply basic power and essential systems energy needs inside my pocket-sized dwelling. My electric needs are low to brainstorm with, but I practise have to lookout man it and reduce loads especially during the Fall and Winter months. Unless your system is enormous (and enormously expensive) you will have to keep an heart on things anyway…

I have integrated the ability to balance (select) my individual loads to exist sourced from either 'grid' or 'solar/batteries/inverter'. I've installed two (Reliance Controls) 10-excursion transfer switch boxes for 20 circuits from my mains panel. Information technology makes the organisation entirely 100% flexible for balancing loads and demands throughout the year.

My Reliance Controls A510C transfer switches shown below. ten circuits each. I installed two of them. Gives me groovy control over balancing seasonal load differences and PV system variances due to conditions and seasons.

DC Cable Size Between Connections

How big should the cables be?

First you will need to summate the maximum current that could flow through the diverse interconnecting cables before you choose the proper cable size.

Cables must be sized to comport the maximum load that the system could deliver. Undersized cables will issue in overheating, and even melted connections. Worse yet, it could become a potential fire hazard.

At that place are three maximum DC electric current specifications to figure out:

1. DC Charger charging current (charger to battery banking company).
ii. DC Load need from the inverter (battery bank to inverter).
3. DC current flow within the bombardment banking company interconnects.

Battery Charger – Max Current

My solar battery charger is the 'Midnite Solar Classic 200'.

Co-ordinate to its specifications, the maximum charge that it can put to the battery bank at 48 volts is 74 amps (~ 3500 watts). Use the chart below to cull cable size. Give yourself a nice margin!

Inverter – Max Battery Electric current

My inverter is an Outback VFX 3648.

According to its specifications, the maximum overcurrent ampacity is 175 amps and they telephone call for a OBCD-175 breaker on the DC side. Evidently in that location's a built-in surge treatment capability on the DC side to 175 amps.

The inverter only puts out 3600 watts max, which would be effectually 75 amps off the 48-volt bombardment bank for normal max performance. Simply given the inverter'due south over-current rating, I had to become with sizing that cable for 175 amps.

So I chose 00 (2/0) AWG for this portion of the overall excursion.

Maximum Current Inside the Battery Depository financial institution

You volition need to determine how many amps will flow through interconnecting cables of the battery bank. This involves some basic understanding of series-parallel wiring and how it affects volts and amps. I volition presume y'all have that basic understanding… (e.g. Ohms Law)

First, nosotros know that in my example there may be upward to 175 amps pulled from the battery bank (worst case scenario). All the same I have 6 series-strings of batteries all in parallel, so simply 1 sixth of the maximum volition flow through whatsoever one string every bit the strings share the load. Then that works out to exist around xxx amps (of worst case over-current max) flowing through each of the vi strings.

That said, I endeavour non to live on the border, and always oversize with a margin.

Really, for my present installation, I've sized all of my DC cables to meet the 175 amp worst case scenario. Because I had the cable. So all interconnecting cables are 00 (2/0) AWG based on the nautical chart below. However, I didn't need them to be that big. Read on…

My interconnecting cables within my battery bank… I concluded up making my ain after buying some pre-made. This saved some money. I did need 00 (2/0) AWG for the main trunk, only went Way overboard on my series-strings interconnects. I used the same cable (because I had bought it in majority). Instead I could've used something similar 6 AWG, even with a 50% margin. Oh well… at least there's no worries with the ii/0 !

Note: Again, the cable size in the photo to a higher place is style 'overkill' for my series/parallel wiring of my 48 volt battery bank comprised of 24 12-volt batteries. I had the cablevision, and, it certain makes for extremely low cable resistance (grin)…

Cable Size Ampacity Chart

The following maximum amps versus cable size (AWG) come from the NEC version 2011. As far as I know these values are valid equally of today. For more detail though, check with the National Electric Lawmaking as well as your ain zoning laws.

Annotation: I would NEVER design interconnecting cable size anywhere near its maximum amps! That'due south too hot for me! Heat loss equals efficiency loss! Give yourself a broad margin.

– Copper Conductor Ampacity based on 75°C (167°F) reference
– Cable Types: RHW, THHW, THW, THWN, XHHW, USE, ZW

Cable Size (AWG – Judge)	Amps – Ampacity
14 AWG	20
12 AWG	25
10 AWG	35
8 AWG	l
6 AWG	65
4 AWG	85
three AWG	100
ii AWG	115
1 AWG	130
0 (ane/0) AWG	150
00 (two/0) AWG	175
000 (3/0) AWG	200
0000 (4/0) AWG	230

Make Your Ain Battery Interconnect Cables?

Eventually I decided to do-information technology-yourself for making heavy duty cables for my battery banking concern. I purchased majority cable (just pick your size). And a heavy duty cablevision crimper (and the associated wire lugs).

Temco Majority Cable
(view on amzn)

Temco Hammer Lug Crimper
Wire Lugs – Eyelets

[ Read: Battery State of Charge Nautical chart ]

[ Read: The Four Essentials of Off Grid Solar ]

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Source: https://modernsurvivalblog.com/alternative-energy/battery-bank-cable-size/