Max amp draw

ktmrfs wrote:

S Davis wrote:
What is a max amp draw for a pair of Trojan T105s? I am trying to figure out wire sizing.

more than likely the max current you will stuff in them to charge will be greater than the max current you pull. But you need to consider both cases. And both will depend on what you have. 50A charging is not unreasonable with a good charger, 6V jars don't like more than about 30-50A longer term draw. Disadvantage of GC is higher internal resistance which affects battery voltage on larger draw.

Charging will be a 100amp circuit from the trucks alternator and 125amp charger in the 2800 watt Outback inverter.

At 75 amps they are rated for 115 minutes. Of course that is dead. Closer to 45 minutes would be better.
75 x 3 = 225 amps and should be plenty to drive most anything. I assume it would be very rare to actually load the inverter to the max rating. I think you are fine with the 6 pack.

Have you considered going to 8 batteries and 24 volts?

theoldwizard1 wrote:
Instead of trying to figure out what the MAXIMUM possible current that can be pulled from a battery, install a 200A battery post fuse.

I guess I worded that wrong, I was trying to ask what a reasonable amp draw on a pair of T105s would be. The inverter is rated at 280amps so with two pair of T105s that would be 140 amps per pair? And I will have a fuse on each pair Of batteries

Ok so a little clarification, I have four T-105s and will be adding two more. They are within 5’ of a 600 amp buss bar, each pair is wired independently through a battery switch and to the buss bar. I plan on adding a 2800 watt Outback inverter/charger. This is being installed on my truck and will power my commercial cap for work and a truck camper for play.

For the AGM version, the Trojan data sheet shows the short circuit current as 3250A. They don't give this specification for the flooded version. In general, a flooded battery would have a higher internal resistance, and so a lower short circuit current, but I'd guess it's still in the range of thousands of amps.

The proper approach, as others have mentioned, is to size the wires for the maximum current you expect to see based on the connected load or charging circuits, and then provide appropriate overcurrent protection (a fuse or circuit breaker) sized based on the wiring. It is utterly impractical to size the wiring for the maximum current the battery can provide...except perhaps in a situation where you actually need that much current, say for a battery testing and characterization rig.

Bobbo wrote:
To figure out the "max amp draw" that the batteries are capable of, drop a crescent wrench across the terminals. :B

A gold wedding band between the wrench and the diamond plate on the front wall works pretty well too.

Instead of trying to figure out what the MAXIMUM possible current that can be pulled from a battery, install a 200A battery post fuse.

What are you powering with them.. Generally the max amp draw for an RV WITHOUT an inverter is not that great. Each 1141 light bulb is about .8 amp (Figure 1 amp to make the math easy) plus Furnace draws about 3.5 amps. Fridge if 12 volt up to 20 (don't use that option) on AC closer to 2 or 3.

Add 10 amps for "Misc" and you have it

Replace the light bulbs with LED divide by 10 (1 becomes 0.1)

INVERTERS 100 amps per 1000 watts.

Four 105's would be much better.

Or one SiO2 would work. They can do a continuous draw of 320 amps.

Bobbo wrote:
To figure out the "max amp draw" that the batteries are capable of, drop a crescent wrench across the terminals. :B To figure out what size cabling you need, calculate the max amp draw of your RV.

Concur !

Many years ago this actually happened to my brother in law. The battery blew up before the wrench melted.

Batteries are about a close to an INFINITE current source as you can get in a short circuit situation.