battery autonomy

RMP 210, 220, 440LE, 440SE, 440 Omni
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luca.lucci
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battery autonomy

Post by luca.lucci » Fri Oct 05, 2012 9:15 am

Hello,
I'm working with rmp440 le with 70 kg as payload and I need to know how long the battery runs down. I know that it's depend on several factor, so is there some application note about it? Otherwise, can someone provide me some reference data?

Thank you

Craig
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Re: battery autonomy

Post by Craig » Fri Oct 05, 2012 1:33 pm

This is a very difficult question indeed. We are working on a propulsion model for range but it is not yet complete.

For now I would suggest that you drive the platform and monitor the SOC as reported by the system. Using the delta SOC over a known drive profile should allow you to estimate the range you will get using your particular setup.

/Craig
Craig Shaffer
Principal Engineer

STANLEY INNOVATION, INC
www.stanleyinnovation.com

luca.lucci
Posts: 12
Joined: Wed Jul 25, 2012 10:09 am
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Re: battery autonomy

Post by luca.lucci » Sat Oct 06, 2012 6:03 am

Hello Craig,
I would like to know the rmp's autonomy in difference situations, so I'm estimating it by monitoring the current per motor. If I do so I don't have to spend a lot of time discarding the battery for every scenario. So, if I take the max avarage current I can predict how long take the battieries to go down. To do this I have to know the capacity, of course. Am I right if I say that the batteries on rmp 440le are 5.2 Ah with a nominal voltage of 73,6 V? Do you have some of larger capacity? Do you know the efficienty of motor driver circuit?

Luca

Craig
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Joined: Thu Jan 26, 2012 3:02 pm
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Re: battery autonomy

Post by Craig » Tue Oct 09, 2012 11:15 am

Luca,

If you are interested in the range of any platform based on time you need to start with the total energy on-board and divide by the instantaneous POWER being used. This will leave you with the duration or time that the system can operate at a particular power level.
luca.lucci wrote: Hello Craig,
I would like to know the rmp's autonomy in difference situations, so I'm estimating it by monitoring the current per motor. If I do so I don't have to spend a lot of time discarding the battery for every scenario. So, if I take the max avarage current I can predict how long take the battieries to go down. To do this I have to know the capacity, of course. Am I right if I say that the batteries on rmp 440le are 5.2 Ah with a nominal voltage of 73,6 V? Do you have some of larger capacity? Do you know the efficienty of motor driver circuit?

Luca
In this post you talk about the max average current per motor and the battery capacity. Motor current is not the same as battery current. In fact, using CURRENT and not POWER in general will lead you astray from what your trying to get at. The motor voltage changes with RPM and the battery voltage changes with SOC so you cannot negate the affect of voltage in any reasonable range model. To get close you need to be thinking in terms of ENERGY and POWER typically expressed in Wh and Watts.

Also to look at how far the platform can drive the propulsion batteries are not the only consideration. If power is being drawn from the auxiliary battery this too must be considered as it often limits the range of the system at lower speeds.

As for your direct questions
-All of our batteries have approximately the same name plate capacity of 380 Wh. Many of our batteries ship with higher capacity than that because we slightly de-rate our batteries. Another factor to consider for battery capacity is that the machine doesn't get to use all of the capacity. We typically shutdown the machine when the battery reports low SOC, however, this can leave as much as 5% of the nameplate capacity in the pack.

-We do know the efficiency of the motor drive circuit, however, that is really only going to add confusion at this point. There are loads of factors to consider (battery inefficiencies, motor inefficiencies, gearbox inefficiencies, wheel and tire inefficiencies, etc.. A purely numerical model with any reasonable accuracy would require several years to develop and require deeper access to the system than we allow customers. Besides most numerical models simply fall apart when you talk about scrub steering where forward velocity is 0 yet power is still being burned at an incredible rate.

Craig
Craig Shaffer
Principal Engineer

STANLEY INNOVATION, INC
www.stanleyinnovation.com

luca.lucci
Posts: 12
Joined: Wed Jul 25, 2012 10:09 am
Contact:

Re: battery autonomy

Post by luca.lucci » Mon Oct 15, 2012 6:47 am

I understand your point of view. So I will try to monitor the soc parameter.

Thank you

Luca

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