what is difference between DC Power Supply and Vehicle Battery ?

In our lab, we power minivan power folding seats with 0 - 20V   0 - 50A DC Power Supply.  These power folding seats are powered with DC Motors.

Before we release our  embedded controller that controls the seat travel, we test with real minivan vehicle battery?  Why is it necessary to test with real vehicle battery?  Isn't the voltage in vehicle battery fixed?  If yes, we can just dial that fixed voltage in our bench power supply.  Why do we need to test with real vehicle battery ?
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naseeamAsked:
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JohnBusiness Consultant (Owner)Commented:
In simple terms a vehicle battery put out less than 20 volts (nominally 13 volts) at WAY more potential amperage. A vehicle battery can put out hundreds of amps for a short period. A power supply (even 50 Amps) is no match for this.

So testing with a vehicle battery will test real world operation at 13 volts (not at your 20 volts) to see how the seat works in the vehicle environment.

Try setting your power supply for 13 volts and see if the seat works. If it does and meets your specifications, then you are probably fine.

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Dave BaldwinFixer of ProblemsCommented:
The main difference between a lab power supply and a battery is that the power supply has circuits to maintain the voltage under load whereas the battery voltage will drop at least a little under load.  You should also test your circuit on the battery when the engine is not running.  Batteries can drop below 12 volts open circuit and when that happens, the internal resistance goes up and the voltage under load goes down.  There really is quite a difference between the lab power supply and a car battery.
Michael-BestCommented:
A car battery is rated at 12 Volts but actually is fully charged at 12.6 Volts.
Alternator output is 14.5 Volts.

The test with a real vehicle battery is to have test results from a real vehicle environment using the entire circuit from battery to the power folding seats DC Motors.

I also think that the test should be done both with the engine off and also with the engine running.
jmcgOwnerCommented:
Also, voltage supplied in a vehicle is not exactly constant. Your system needs to be able to withstand the vagaries of the somewhat dirty power supplied. It might be worth getting a real-time recording of vehicle power variations under numerous conditions and build some of those variations into your lab test setup.
JohnBusiness Consultant (Owner)Commented:
@naseeam - Thank and good luck with your electrical testing.
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