Battery drain

[nemmi69]

Little confused over battery drain. It is stated in one of the links

"The motor will draw 42 Amps.
With just one batterypack with 30Ah,
that's less than 43 minutes of driving time"

How much can you draw ultimately? Could you draw 400A for 4 minutes?

Sorry if this sounds brainless but I am new to this.

 

[itsid]

depends on the battery pack.
In fact you'll find a sticker on most batteries stating the CA of a battery (cranking amps)
for most car batteries that'll be between 400 and 600 Amps
half of that you can draw all day long (well until the battery is drained of course)

if you do not have a CA rating on your battery then go with the capacity as your indicator..
generally with car batteries you should be safe drawing up to three times the capacity rating
(a 30Ah battery should easily deliver 90 Amps without failing, a 60Ah battery 180Amps etc.)

If you question is about the limits of a battery and we talk car batteries (lead acid gel packs etc.. not Lithium batteries from the RC shop )

if you talk mpg that quote is misleading without context.

what it tells you is a rough estimate about 'driving time' based on the motor rating.
motors do not a constant amount of power while driving..
the draw much more when accelerating and much less to none when decelerating,
and the average is dependend on the driver and road (uphill more, downhill less.. leadfoot more, steady cruiser less...etc.)

it's a hint.

to answer your question.. maybe.. maybe just three and a half minutes and then you'll have to wait for the battery to settle back in and able to deliver those 400 amps for another 30-35 seconds.
that again depends on the batteries.

'sid

 

[nemmi69]

Well this is for a proposed hybrid (may be an A3 if the other half lets me).
Goldenmotor 48V 20kW motor 48V-HPM-20KW
Goldenmotor 48V controller HPC700H/48V840A

I know from their chart that the steady amps are 515A with a peak of 1157A (@ 88.5% efficiency).

I am trying to guesstimate what the consumption would be like for stop-start and ramping to 30mph. This is excluding the engines input and also the regen part. My brain cannot work out the driving time for a single start to 30 mph. Still do not get how you worked out 43 minutes on your example (brain fade ).

 

[itsid]

..Still do not get how you worked out 43 minutes on your example (brain fade ).

I think so...

it's easy if you remember that an hour has 60 minutes

30Ah == 1800Am (Amp minutes)

constantly drawing 42 Amps (assumed value based on the motor spec)
means.. 1800Am/42A = ~ 42.857m (minutes!) 42minutes and about 52 seconds not quite 43 minutes

Now.. your problem is, that you try to guess things that are sooo vague,
that it's basically BS to even try without knowing all involved specs (weight, wheelsize, road inclination, weather, road condition, quality and condition of the bearings .... should I stop now?)

you know it's a 20kW motor... good..
you know it's 48V... good...

Now, let's guestimate with those values then!
20000W / 48V = 416.66(p) Amp

since we only guess let's just say 420 Amps for simplicity's sake.
that'll be about the upper end you'd expect this motor to draw on average over a full charging cycle.

with a small batpack like 30Ah that's not even four and a half minutes
until the battery is dead.

You cannot EVER draw 1157 A with the controller you chose..
it maxes out at 840 Amps in the 48V configuration.
even trying to pull 1157 Amp throuhg it's lines will cause it to either shut down completely ... or worse ... burn through it's mosfets and fail permanently.

just saying

btw I cannot find the specsheet of the 48V version of the motor (only 72 and 96V datasheets)

'sid

 

[nemmi69]

Gaaaaah! thanks for the example for the Ah.

I don't get their bit about peak 50kW as in their example they never hit this. I am guessing occurs at 0 rpm. But if they knew this why does their biggest controller not handle it?

I did a quick conversion of their I(A) from 96V to 48V and it goes from 45A (4060 rpm) to 515A at its peak (around 3140 rpm).

The fun bit is that for a 2001 A3 1.6l the 0-60 is 11 secs 1/4 mile 17.8 secs and weighs 1090kg (power 100bhp - torque 148 Nm). So with the weight gain if I can match this I will be a happy bunny. Also, since it only has to start the engine first then, once clutch is engaged, help the car accelerate the motor is not doing all the work.