Admiral B2 and Alltrax400

[JohnnieB]

Originally Posted by Neill7082

1. I always recharge after each use.
2. Seems I didn't realize that the break in cycle makes that big of difference.

1.

2. A battery pack's storage capacity is a major factor in how far the voltage drops when amps are drawn. The lower the storage capacity (AH rating), the greater the voltage drop per amp being drawn.

This voltage drop is typically expressed as Volts dropped per 100A drawn and the nominal value for a standard 48V pack (6x8V - 170AH) is 1.5V/100A. Or at least, that is the value typically used by motor manufacturers when they dyno test their products. At the max battery current draw (252.9A) the voltage had dropped to 41.8V and the starting voltage was 50.9V, so the drop was 3.6V/100A. That is more than twice the ideal amount, but it also includes voltage losses due to resistances in the high current cables, connections and contacts.

You have a relatively new 200A solenoid and 2Ga cables, so the resistances in the cables connections and contacts are likely to be close to the intrinsic (unavoidable) values, meaning the high amount of voltage drop is likely to be due to low storage capacity of the batteries.

Trojan sells five models of 8V batteries with storage capacities from 160AH to 204AH. The T-875 (8V - 170AH) is typically the one used for 48V packs, so I'll use it for example.

New, it has about 127.56AH at 80°F and that drops to about 95.6AH at 40°F. In other words new off the shelf 170AH batteries operating in cool weather act like old batteries nearing the end of their useful lifespan. Fortunately, they will get better as they are broken in, but won't reach their full rated capacity until they are being operated at 80°F.

----------------
Another log file after two dozen charge cycle will hopefully show some improvements.

[Neill7082]

Thanks for the info/help JohnnieB!!! I defiantly will get a lot more charges under the cart and then post the info back up.

It has been in mid 40s lately. Give it a day or two and Texas will be back in the 80s again.

[JohnnieB]

It is the temperature of the electrolyte and plates in the batteries that determine the relative storage capacity and batteries have a huge thermal mass, so the battery temperature will be closer to the overnight low rather than the afternoon high.

In other words, your batteries will perform better next summer.

Here is a chart from Trojan showing storage capacity vs battery temperature.

In a nutshell: 100% at 80° and 50% at 0°F with the line between the two being fairly linear, so the decrease in storage capacity is roughly -0.625%/-1°F,

[scottyb]

In other words, your batteries will perform better next summer. JB

I hadn't seen that chart - great info

[JohnnieB]

Page-23 of Trojan's latest User's Guide (4/30/2019) --- Attached.

The chart and the text didn't match in earlier editions. Text said AH dropped to 50% at 0°F, while the chart showed about 60% at 0°F. Looks like the text was correct and they corrected the chart.