Voltage drop under power

[kward]

Just curious, I switched from 6 Trojan T890's that had 190 amp hour rating to 8 Interstate 6v with 225 amp hour rating. Not quite sure but is seems that the voltage drop under power in more since switching. Mine drops to around 45 or 46 volts under power after a full charge, seems like it used to only drop to around 48. Can anybody chime in and tell me what there voltage drop is?

[scottyb]

New batteries are not full strength, it takes many cycles for them to reach full capacity.
Could this be part of the problem?

[kward]

What amount of drop should I expect once the batteries have been conditioned?

[JohnnieB]

Originally Posted by kward

What amount of drop should I expect once the batteries have been conditioned?

Theoretically, you have increased your battery pack ampacity by about 18%, so the voltage drop should decrease by about 18%.
If you were dropping from 51V down to 48V before, you should only be dropping to about 48.5V, if the the relationship between voltage drop and ampacity is linear.

Of course, this does not take into consideration the resistance that exists in the high current connections and components, which cause a voltage drop irregardless of battery capacity.

[wizardket]

Originally Posted by scottyb

New batteries are not full strength, it takes many cycles for them to reach full capacity.
Could this be part of the problem?

I will go with Scotty on this. Also the internal resistance of Interstate and Trojan are probably not the same.

[JohnnieB]

Originally Posted by wizardket

I will go with Scotty on this. Also the internal resistance of Interstate and Trojan are probably not the same.

I'm with Scotty on this also, but kward's question stipulated, "once the batteries have been conditioned".

Not only is the internal resistance between Interstate and Trojan batteries different, the internal resistances of the "identical" batteries in a battery pack are different.

WARNING: Technical stuff follows.

At the molecular level, the voltage produced by the electro-chemical reaction is the same whether the cell (or battery) is fully charged, fully discharged or anyplace in between.
When we say that a cell (or battery) is being discharged, what we are actually saying is that the cell's internal resistance is increasing.

Since the internal resistance is in series with the poles of the cell, the voltage measured at the poles will be the intrinsic voltage of the chemistry, less the voltage developed across the internal resistance due to the current passing through it. This is true of all primary and rechargeable cells/batteries.

If the batteries in your pack all measure the same terminal voltage, it means that your voltmeter does have enough digits to the right of the decimal point to detect the differences in voltages.
(Of course these slight differences are meaningless until the get over the 0.1V range on pack made up of 6V batteries)

Now I gotta go out and send some electrons backwards through the battery of my wife's SLS and reduce the internal resistance so it will send enough current through the starter motor to fire up the Northstar.

[Coltf1991]

John, do you ever get headaches?

But yes break your batteries in first, then monitor the voltage drop. Visit carts unlimited on how to break batteries in!

[JohnnieB]

Originally Posted by Coltf1991

John, do you ever get headaches?

Get - No. Give - Yes.