Battery test. Stop start with 2 batteries.

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Battery test. Stop start with 2 batteries.

Postby gn8691 » Fri Jan 08, 2016 9:04 pm

Hi,
Could you tell me if the PicoDiagnostics software is capable of testing battery(s) and charging systems of these stop start vehicles with more than 1 battery.
I found that some of the auxiliary batteries are small motorcycle types.
Does this interfere with the readings for accurate diagnosis of the main battery and charging system ?
Thanks,
Iain
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Re: Battery test. Stop start with 2 batteries.

Postby Steve Smith » Mon Jan 11, 2016 2:32 pm

Hello Iain and thank you for the post

This is an interesting question and I would like to know more about the vehicle under test?

Could you let me know which make and model vehicle utilse these small auxiliary batteries for stop start systems?

Have you carried out any testing on such vehicles and would you have a saved file?

Were the test results accurate?

I am assuming the auxiliary battery would be in circuit to prevent surge under cranking having an adverse effect on electrical systems.

I can see how an auxiliary battery would also enable longer engine stop conditions with high auxiliary circuit load in heavy traffic conditions.

I would like to obtain a wiring diagram to see how these batteries integrate with the vehicle battery and cranking circuit

Any feedback would be most helpful

Just reading this back, sorry for all the questions, I bet you wish you had never asked!

Take care.......Steve
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Re: Battery test. Stop start with 2 batteries.

Postby gn8691 » Mon Jan 11, 2016 5:48 pm

Hi Steve,

I was asked to fit a battery only (genuine Mercedes) and didn't have my pico with me so no saved files.
The vehicle is a 2012 Mercedes B Class 180 cdi with stop start.
The main battery is a AGM 80 ah , 800 CCA.
The small battery I didn't remove and didn't see the specifications on it but it was a small motorcycle battery tucked below glovebox under the carpet / insulation.
I disconnected both before changing the main battery which has rectified the fault of poor starting.
Old Battery not holding a good charge even when disconnected from vehicle.

Regards
Iain
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Re: Battery test. Stop start with 2 batteries.

Postby volrem » Tue Jan 12, 2016 8:32 pm

Volvo also uses two batteries on some vehicles. For example S40 2011 1.6D Drive.

This car has 8Ah 120A secondary battery.

I haven't tested but technical information stays that during Start-Stop autostart condition main battery powers only starter motor and secondary battery powers the rest. There are two relays for that and also a diode. Diode lets power from main battery to rest of the consumers also if secondary battery is too weak.

When doing normal starting then secondary battery is disconnected so it doesn't affect battery test.

But this logic may be different for other makes and models.
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Re: Battery test. Stop start with 2 batteries.

Postby Steve Smith » Wed Jan 13, 2016 10:00 am

Thank you both for the posts and thank you to our friends at Mercedes to the following information which is almost identical to Volrem's Volvo.

In a nutshell the Eco stop/start system isolates the main battery from the vehicle electrical system such that it is only connected to the starter motor during cranking.

During the cranking phase the 12 Ah Aux battery is then connected to the vehicle electrical system to ensure continuity of power supply.

This arrangement will therefore reduce surge and the perceived "power dip" which is often a characteristic during the Eco stop/start restart phase with heavy auxiliary load (Such as sitting in traffic with headlights and heater on etc.)

Charging of both batteries is controlled via the on- board engine and battery management systems.

From the description of this system it would not appear to effect the vehicle battery test procedure using Pico Diagnostics as during crank and start we run with the main battery.

It would be interesting to see how the connection of the auxiliary battery effects the charging system once connected to the alternator, when the engine has started.

This can only apply additional load to the generator and increase charging current and “ripple” which will produce a “green” pass result for the charging system

Like anything Iain the proof is in the pudding, if you get chance to run such a test I would be intrigued to know how the results pan out.

I hope the posts above help and thank you again, take care......Steve
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Re: Battery test. Stop start with 2 batteries.

Postby gn8691 » Wed Jan 13, 2016 10:52 am

Thanks for all the replies and valuable information.

I'm pretty sure i've gained a customer so I will perform a Battery test when I next see the vehicle.

Any other stop start vehicles i see will also be tested from now on and saved.

Thanks again,

Regards,
Iain :D
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