# Re: [EVDL] Slow due to 96V pack?

```I don't think that math is right but you won't get 100% efficiency out a
controller.
Current out of a battery is not calculated based on internal resistance.
Internal resistance or Impedance of a battery can be modeled and measured but
it doesn't act like a normal load. It's a chemical reaction and different
chemistries will give you different currents.
If it is not due to limits on the controller and the efficiency drop then I
would say the batteries aren't at full capacity any more.
The battery industry uses a 100-hour rate as an index to compare batteries of
different types and sizes. The 100-hour rate is the amount of Ahs the battery
will deliver during a 100-hour discharge. The capacity of a battery, in Ahs, is
a dynamic number that is dependent on the discharge current. ```
```
For example, a battery that is discharged at 10A will give you more capacity
than a battery that is discharged at 100A. With the 100-hr rate, the battery is
able to deliver more Ahs than with the 20-hr rate because the 100-hr rate uses
a much lower discharge current than the 20-hr rate. Both rates are used as
baselines. Either rate, however, will give you the same view of a battery. A
higher capacity battery will have higher 5 and 20 hour rates than a battery
with lower capacity.
They publish tables that you can look up to see these values.

From: Lee Hart via EV <ev@lists.evdl.org>
To: Electric Vehicle Discussion List <ev@lists.evdl.org>
Sent: Monday, September 11, 2017 11:40 PM
Subject: Re: [EVDL] Slow due to 96V pack?

From: lektwik via EV <ev@lists.evdl.org>
>96V  = Slug

Not necessarily; but in this case, probably correct.

Here's my guess: A 6v golf cart battery has an internal resistance of about 5
milliohms (0.005 ohms). A 96v pack has 16 of them; so the resistance is 0.005 x
16 = 0.08 ohms. Let's say the Zilla limits voltage to 72v (i.e. it won't pull
the pack below 72v). Then the most current you can get is I = V/R = (96v-72v) /
0.08 ohms) = 300 amps.

In practice, the resistance of the pack is a bit higher due to the wire and
connectors. So a 200a max current is probably the most you can draw from the
golf cart batteries before their voltage under load falls to 72v.

Now, if you had a different kind of batteries with less internal resistance, or
a controller that would cheerfully pull the battery voltage even lower, you'd
have a lot more current, and peppier performance.

For example, my old ComutaVan had a 72v pack of golf cart batteries, and a
contactor controller. It would cheerfully pull 1000a from the batteries, and
spin the tires if you "floored it" from a dead stop. I tried a Curtis 1221 400a
controller; and it was *worse* than the contactor controller for accelleration,
because it never came anywhere near 400a due to voltage sag.

--
Excellence does not require perfection. -- Henry James
--
Lee A. Hart http://www.sunrise-ev.com
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