Max amp draw

[S_Davis]

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

[pianotuna]

Here is a link to Mex's suggested resource.

https://batteryuniversity.com/

It is a living entity.

[MEXICOWANDERER]

My fingers will not support a lot of writing. Sorry folks, but your excerpts are incomplete 🙂

BATTERY UNIVERSITY has had mutiple peer reviews including my own. I heartily endorse studying this free resource.

[Chum_lee]

BFL13 wrote:

pianotuna wrote:
PbO2+Pb+2H2SO4 -- ChargeDischarge -- 2PbSO4+2H2

BFL13,

If I am reading that chemical equation correctly Hydrogen is produced on discharge.

From;

https://www.sciencedirect.com/topics/engineering/sealed-battery

The link says the last part is "2H2O" not "2H2" but it is confusing.

My Battery Bible--

http://www.bestconverter.com/Books_c_67.html

just says that on discharge, " the hydrogen ions in the electrolyte move to the positive plates and combine with the oxygen to form water---"

on recharging, "the positively charged hydrogen ions are attracted to the negative plates where the hydrogen combines with the lead sulfate to form lead and sulfuric acid. When most of the lead sulfate is converted to lead, hydrogen bubbles form at the negative plates and rise through the electrolyte.....oxygen appears at the positive plate when this process is near completion. the formation of the gas indicates the battery is nearing complete charge..."

Those chemical equations are "generalized" to simplify the learning process. In reality, there are many other side reactions which occur, especially as batteries age and the plates/electrolyte becomes contaminated. (with sodium, potassium, magnesium, calcium, iron, fluoride, chloride, iodide, etc. from using other than distilled water) Generally, it's true that when recharging lead/acid batteries, more gas is generated than when discharging. The point is, if you are going to discharge wet cell batteries at a high rate over an extended period of time, eventually they will need to be recharged. (probably at a high rate also) The battery compartment(s) need adequate ventilation. That's my point! Overlook that and eventually, . . . . . . BOOM!

Chum lee

[pianotuna]

Hi BFL13,

There was a slider--so I did not copy the entire equation--sorry about that!

[BFL13]

pianotuna wrote:
PbO2+Pb+2H2SO4 -- ChargeDischarge -- 2PbSO4+2H2

BFL13,

If I am reading that chemical equation correctly Hydrogen is produced on discharge.

From;

https://www.sciencedirect.com/topics/engineering/sealed-battery

The link says the last part is "2H2O" not "2H2" but it is confusing.

My Battery Bible--

http://www.bestconverter.com/Books_c_67.html

just says that on discharge, " the hydrogen ions in the electrolyte move to the positive plates and combine with the oxygen to form water---"

on recharging, "the positively charged hydrogen ions are attracted to the negative plates where the hydrogen combines with the lead sulfate to form lead and sulfuric acid. When most of the lead sulfate is converted to lead, hydrogen bubbles form at the negative plates and rise through the electrolyte.....oxygen appears at the postive plate when this process is near completion. the formation of the gas indicates the battery is nearing complete charge..."

[pianotuna]

PbO2+Pb+2H2SO4 -- ChargeDischarge -- 2PbSO4+2H2

BFL13,

If I am reading that chemical equation correctly Hydrogen is produced on discharge.

From;

https://www.sciencedirect.com/topics/engineering/sealed-battery

[BFL13]

Chum lee wrote:
How well ventilated is your battery compartment, if one exists? In high draw conditions, wet cell (lead/acid) batteries will eventually off gas hydrogen and oxygen in large enough quantities to go boom. (not good)

Chum lee

AFAIK (?) there is no gassing on discharge. The hydrogen is combining with oxygen to make water.

On recharging you will get get gassing once the voltage rises to "gassing voltage" of about 14.2v and you get acid instead of water being made.

[S_Davis]

Chum lee wrote:
How well ventilated is your battery compartment, if one exists? In high draw conditions, wet cell (lead/acid) batteries will eventually off gas hydrogen and oxygen in large enough quantities to go boom. (not good)

Chum lee

Yes that can be an issue, I worked on a off grid project 12,000sqft house on a 40 acre island in the San Juan islands where the they put one of the main battery boxes in the basement and just about launched the house.


The four are in vented battery boxes in the front of the truck bed, the other two will be mounted to the truck frame rails with custom brackets. The two in the camper will be in factory battery box and the two in my commercial cap will be in a sealed vented box.

[Chum_lee]

How well ventilated is your battery compartment, if one exists? In high draw conditions, wet cell (lead/acid) batteries will eventually off gas hydrogen and oxygen in large enough quantities to go boom. (not good)

Chum lee

[S_Davis]

time2roll wrote:
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?

I will eventually have 8 batteries in the system, six on my truck and two in my work cap and truck camper. I want to use the truck for charging so going 24 volt would be an issue.

[S_Davis]

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.

[time2roll]

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?

[S_Davis]

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

[S_Davis]

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.