Powering devices and Ignition questions

dnme

Hi there,

Back again with another question on my beloved 1998 Toyota Corolla.

(1)
I have a few devices that are require power such as a stereo, phone charger etc. With the car off, when I turn the key in the ignition one notch, everything gets power and that's great. However when I then turn the key fully to start the engine, the engine turning briefly kills power to my devices and they restart. This is annoying, the stereo takes about 15 secs to start for e.g. Is there any cure for this? i.e. what I want is for the device to stay powered through the engine turn/start process. Say I'm parked up with engine off listening to radio, I dont want to loose radio when I then start the engine.

(2)
I have a device in my car (an xDriven camera that I got very cheap off ebay. ) that I would like to remain powered for a set time after I switch off the ignition - say 20 minutes or so. Is it possible to do this? and if so how?

Many thanks

colm_mcm

If the battery is on the way out this will happen, since getting a new battery in my (diesel) car, this doesn't happen any more.
I think it's the strain on the system when the engine starts rather than a design issue with the ignition.

DublinDilbert

Some cars will drop out the power to accessories during cranking, but more often than not its the accessories themselves that are powering down. During cranking the battery voltage will go from 12V to approx 5V. Most accessories don't like 5V's and will reset.

In theory you could wire up a small 12V alarm battery with a charging diode, which would keep stuff powered during cranking, then charge off the car once its up and running.

You can probably buy a time delay relay from radionics that would allow you to leave stuff powered up after the car has been turned off, but that might cause other issues, eg sleep current. you might be able to buy something off the shelf for this, but it could be made up easy enough by someone who knew what they were at.

cb900ie

Does the engine turn over slowly when you are starting the engine? If it does, the battery is in poor condition, the voltage is dropping below 10 Volts (disagree with DublinDilbert!) and cannot supply enough current to supply the radio and the starter motor so it supplies the starter motor only.

DublinDilbert

On cranking the battery voltage will go much lower than 10v.

Many automotive ECUs will be designed to turn off during cranking, to conserve power.

The battery would still be able to supply current for the radio cb900ie, if it's suppling 400A, 1A extra for the radio should be no problem.

The radio won't like the voltage drop and will turn off during it. Some vehicles will also turn off non essential loads over the CAN bus just before cranking.

I design automotive electronics for a living so do have an idea what I'm talking about it...

crosstownk

DublinDilbert wrote: »

On cranking the battery voltage will go much lower than 10v.

Correct. The current required by the starter is massive in relation to accessories. The starter has larger wires and requires more current so it gets it - path of least resistance. Other systems are starved of current momentarily and temporarily shut down.

DublinDilbert

Not to split hairs, but the other circuits aren't starved of current, they will however see a voltage drop.

A car company will specify for each electrical unit what its functional status should be during cranking. Eg engine ecu & fuel pump must be fully functional, others will turn them selves off.

dnme

cb900ie wrote: »

Does the engine turn over slowly when you are starting the engine? If it does, the battery is in poor condition, the voltage is dropping below 10 Volts (disagree with DublinDilbert!) and cannot supply enough current to supply the radio and the starter motor so it supplies the starter motor only.

No battery is fine

cb900ie

@DublinDilbert- maybe you know about electronics, but you are totally incorrect to say that battery voltage drops to 5V during cranking. With 5V across the battery during cranking, the engine rpm would be as low as 20rpm because the current flow to the starter is reduced.

DublinDilbert

cb900ie wrote: »

@DublinDilbert- maybe you know about electronics, but you are totally incorrect to say that battery voltage drops to 5V during cranking. With 5V across the battery during cranking, the engine rpm would be as low as 20rpm because the current flow to the starter is reduced.

The voltage on the battery during cranking will depend on the size of the engine, size of the battery, condition of the engine (eg compression), condition of the battery, temperature, engine oil etc etc etc..

There is no one value that is the same for all cars. I'm saying that most car companies will test that critical components will work down to approx 5 or 6V during cranking. Below about 9V all non critical stuff will be designed to stop working.

cb900ie

DublinDilbert wrote: »

The voltage on the battery during cranking will depend on the size of the engine, size of the battery, condition of the engine (eg compression), condition of the battery, temperature, engine oil etc etc etc..

There is no one value that is the same for all cars. I'm saying that most car companies will test that critical components will work down to approx 5 or 6V during cranking. Below about 9V all non critical stuff will be designed to stop working.

Firstly, I accept that I did not explain the radio current issue very well.

Secondly, a fully charged battery with 1.28 kg/L reading per cell has 12.6V open circuit, and the battery has a low resistance. While its current capability depends on its CCA rating, compression ratio, number of cylinders, fuel type, coolant temperature, ambient temperature, engine oil temperature and viscosity etc., the generally accepted minimum potential difference measured across the poles of a fully charged battery during cranking should be no less than the 9-10V range (definitely not as low as 5V).

If it reads less than that at terminal 30 of the starter motor with a fully charged battery, there may be issues with voltage drop on the positive or earth side of the starter motor circuit due to unwanted resistance, or with the starter motor itself for example, and this excessive voltage drop will consequently cause a weak spark at the plugs and reduced lift at the injectors for example. Also, subject to correction, a 1998 corolla has one ECU and does not have CANbus.

May be that I also know what I am talking about, but never mention it...

DublinDilbert

That is actually a good point, back to the original problem why are all the OP's devices resetting if the voltage is never getting below 10V?

10V should be plenty to run his sat-nav, stereo etc etc...

langdang

Dunno about more modern cars (they may be setup to avoid the resetting of gadgets and gizmos) but my 98 mazda (so more than likely same setup as a corolla) switched out all the Accessory stuff before cranking.

I had a problem with my ignition switch so had to bypass it with a pushbutton:
1)switching key to start position switched out the radio etc but didn't engage the starter due to a break in that circuit. A pushbutton was used to complete the circuit to the starter relay. IIRC it was possible to hold the key in that position as long as you wanted but the radio would not powerup again til the key returned to ACC position.
2)It was also possible to crank the engine via the pushbutton when the key was in the ACC position - No resetting of radio or Bluetooth handsfree.

cb900ie

As you probably know, most stereos have 2 positive feeds, one of which is for the memory and is generally connected to a terminal 30 ('constant live') feed and the other connected to a terminal 15 ('ignition live') feed. However, if either or both feeds is/are connected to the Accessory position feed from the ignition switch, particularly the main feed, it could cause the stereo to power down during cranking. As DNME has now clarified that the battery appeaers to be cranking the engine normally, I would suggest that the Accessory position feed could be the cause of the problem. To rule out or prove this, I would suggest disconnecting the 2 positive feeds into the stereo from their current feed and running a new feed to both connections directly from the + side of the battery.

The other possibility is that it has a system like the x-contact relay fitted to VW, that powers down all non-engine management circuits during cranking, but I don't believe the Corolla has this.

dnme

I have the stereo fitted via a proper cable harness adapter (ISO => Toyota) I think. So all the cabling to the stereo is correct. It has it's memory permanent live feed etc.

Is it normal for devices to restart on cranking? What I would like to achieve, is for stereo to stay running and also any device that is connected to cigarette adapter.

cb900ie

dnme wrote: »

I have the stereo fitted via a proper cable harness adapter (ISO => Toyota) I think. So all the cabling to the stereo is correct. It has it's memory permanent live feed etc.

Is it normal for devices to restart on cranking? What I would like to achieve, is for stereo to stay running and also any device that is connected to cigarette adapter.

Generally, it is not normal for e.g. the stereo to completely shut off during cranking. However, even though you used the correct interface adaptor for the radio, it is possible that the main feed for the stereo is coming from the ACC position on the ignition switch into this adaptor, thereby shutting down your aftermarket stereo during cranking.

I still suggest trying a constant live from the battery to the main feed on the adaptor to rule this out or prove it.

Another slim possibility is a fault within the electrical section of the ignition switch (the piece screwed onto the back of the ignition switch).

Do you have a multimeter by any chance?

dnme

cb900ie wrote: »

Generally, it is not normal for e.g. the stereo to completely shut off during cranking. However, even though you used the correct interface adaptor for the radio, it is possible that the main feed for the stereo is coming from the ACC position on the ignition switch into this adaptor, thereby shutting down your aftermarket stereo during cranking.

I still suggest trying a constant live from the battery to the main feed on the adaptor to rule this out or prove it.

Another slim possibility is a fault within the electrical section of the ignition switch (the piece screwed onto the back of the ignition switch).

Do you have a multimeter by any chance?

No multimeter, and I am very reluctant to wire straight from the battery to the stereo. I would have no isolator and would be solely dependent on the fuse in the stereo. Anyway if it is normal for stereos to shut down during cranking, then the fat lady has sung already wouldn't you say?

cb900ie

dnme wrote: »

No multimeter, and I am very reluctant to wire straight from the battery to the stereo. I would have no isolator and would be solely dependent on the fuse in the stereo. Anyway if it is normal for stereos to shut down during cranking, then the fat lady has sung already wouldn't you say?

The original system was fine for the original accessories but there is nothing wrong with modifying it to take account of modern accessories and requirements, as long as it is done safely and correctly. For example, there is nothing wrong with running a fused constant feed from the plus side of the battery to the stereo feeds in the adaptor, on condition that you remove the original ACC feeds first. If you are concerned about isolating the radio before you leave the car, you could run the feed from the battery through a standard 4-pin relay controlled by a switch on the dash.

Eric Cartman

dnme wrote: »

I have the stereo fitted via a proper cable harness adapter (ISO => Toyota) I think. So all the cabling to the stereo is correct. It has it's memory permanent live feed etc.

Is it normal for devices to restart on cranking? What I would like to achieve, is for stereo to stay running and also any device that is connected to cigarette adapter.

Yes, the only real way to avoid devices resetting on cranking is a 2nd battery, split charge diode and a relay to turn it all on when the car is in ACC mode ,

DublinDilbert

cb900ie wrote: »

@DublinDilbert- maybe you know about electronics, but you are totally incorrect to say that battery voltage drops to 5V during cranking. With 5V across the battery during cranking, the engine rpm would be as low as 20rpm because the current flow to the starter is reduced.

I think you've misunderstood me, I never said that the voltage would be 5V for the entire cranking period, clearly as the starter begins turning it will generate a back emf and its' current draw will decrease.

During the later stages of cranking, depending on the battery condition the battery may well be at 8V. But as the starter is a series motor it will take massive start up current, literally limited by its armature, cables and battery resistance.

Check out page 65 of:-
http://www.fordemc.com/docs/download/EMC_CS_2009rev1.pdf

The value given for the voltage at start of cranking is U1 = 5 V. The voltage during cranking will be U2 which is 9V with a 2 V ripple.

cb900ie

DublinDilbert wrote: »

Some cars will drop out the power to accessories during cranking, but more often than not its the accessories themselves that are powering down. During cranking the battery voltage will go from 12V to approx 5V. Most accessories don't like 5V's and will reset.

In theory you could wire up a small 12V alarm battery with a charging diode, which would keep stuff powered during cranking, then charge off the car once its up and running.

You can probably buy a time delay relay from radionics that would allow you to leave stuff powered up after the car has been turned off, but that might cause other issues, eg sleep current. you might be able to buy something off the shelf for this, but it could be made up easy enough by someone who knew what they were at.

First of all, I did not misunderstand you. I replied to the information as given (see above highlighted).

Secondly, 5V for 15ms at -40 degrees- does this have relevance to the original post? I still maintain that 9-10V is generally accepted minimum PD across the battery when cranking during normal ambient temperatures using a voltmeter, and assuming a fully charged battery etc. but I can provide references if you require.

Finally, some starter motors are series wound and some are series-parallel