Will People With Electrical Knowledge Please Check This

[Penelope Stopit]

Got there in the end




Moderators I have already posted this diagram to the TVR forums as there are some good electrical techies that visit there, I am hoping to get more sensible opinions by also posting it here. Please dont delete this as a duplicate unless you must. Thank you in advance

Below is a 18 Volt cranking diagram that I have put together, the following is copied from my topic posted to the TVR forum

Please, I need your opinions on this diagram. Although I have titled this topic "18 Volt Cranking" it gets better than this, I have calculated a voltage of approximately 14.8 / 15 volts at the starter motor during cranking and believe this will have no drastic effect on the starter motor or its solenoid if put into long term use
Obviouly all the cables from the batteries to the solenoids contacts are of the heavy duty battery cable type
The diagram is drawn to show the circuit with ignition on, when cranking the relay will switch in and the two continuous current solenoids will drop out followed by the two standard starter solenoids pulling in. Battery 3 is in parallel with battery 2 and they are in series with battery 1 when the engine is running and they all charge from the vehicle alternator. During cranking battery 3 is in series with batteries 1 and 2 and 18 volts is supplied to the starter motor, this voltage obviously drops once the starter motor kicks in
Battery 4 if fitted would aid in balancing the batteries out (2 x banks of 2 parallel connected 6 Volt batteries connected in series with eachother will improve the charging conditions and give a better battery life)
I am aware of the fact that there would be a problem if at least one particular solenoid did not drop out before the other pair pulled in and I will be adding a fix for this tomorrow
Thank you in advance

Edited by Penelope Stopit on Tuesday 18th July 18:33

[tapkaJohnD]

Why not buy a HiTorque starter motor?

JOhn

[GreenV8S]

That looks like a complex setup and I haven't taken the time to look for all possible failure modes, but it looks as if it has the potential to form a short circuit if a relay hangs while switching the batteries around. It also introduces several sets of contacts into the main current path, which adds cost, voltage drop and reliability issues.

I suspect you may have introduced a battery balance problem since you are charging in parallel and discharging in series i.e. the two parallel batteries will require twice as much charge as the single battery you are charging them in series with. You could get around that by even more complex arrangements, but it's not obvious why you need any of that complexity.

Is this just a thought experiment, or are you trying to solve a specific problem?

Edited by GreenV8S on Monday 17th July 11:16

[stevieturbo]

Bizarre indeed.

[Penelope Stopit]

GreenV8S said:

That looks like a complex setup and I haven't taken the time to look for all possible failure modes, but it looks as if it has the potential to form a short circuit if a relay hangs while switching the batteries around. It also introduces several sets of contacts into the main current path, which adds cost, voltage drop and reliability issues.

Is this just a thought experiment, or are you trying to solve a specific problem?

Thank you for your input
Yes there is a problem with the timing of solenoids pulling in when others haven't tripped out and I have mentioned this in my OP, I have the solution for this probem and will post it up later
This isn't an experiment, I have viewed several methods that switch from 24 Volt cranking to 12 Volt running using a series parallel solenoid and they do have their weak points like most work arounds do, the biggest downside of 24 Volt 12 Volt switching is that 24 Volts is often supplied to a 12 Volt starter motor and this is too high hence it not being for everyday use as the starter motors will quickly fail, the other downside of a series parallel solenoid is that once one contact inside the solenoid has failed the solenoid is of no use.
Using seperate solenoids makes this circuit more serviceable and the cost of one solenoid if shopped for wisely will work out cheaper than a series parallel solenoid
The four solenoids would be wired in close proximity of eachother using copper bars or heavy duty cable so as to eliminate man made volt drops

Please do look for anything that I may have overlooked, your and others findings are most welcome

[Penelope Stopit]

stevieturbo said:

Bizarre indeed.

This is the difference in the way people look at and approach solutions to problems
If you will kindly inform me of what you find is bizarre about a 18 Volt cranking circuit it may be of some help to me
Thank you in advance

[Penelope Stopit]

tapkaJohnD said:

Why not buy a HiTorque starter motor?

JOhn

This is definitely the way forward when they can be found for a particular engine although even then a higher voltage when cranking will make a big difference

[stevieturbo]

Penelope Stopit said:

This is the difference in the way people look at and approach solutions to problems
If you will kindly inform me of what you find is bizarre about a 18 Volt cranking circuit it may be of some help to me
Thank you in advance

And as Green said...what exactly is the problem you are trying to solve with this extremely complicated "solution" ?

[anonymous-user]

I know TVR owners like to mess around and modify their cars, but in this case i can;t see the point?

If your car doesn't start with a normal 12v battery and starter, the engine's f**ked. Fix the engine, don't modify the car to try to mask a failure!


All this extra wiring and contactors is likely to be a) highly unreliable and b) a massive fire risk when, inevitably, one relay gets a bit sticky, or contact welds on.....



Can you explain why you need 18V to start the engine??

[eliot]

Penelope Stopit said:

tapkaJohnD said:

Why not buy a HiTorque starter motor?

JOhn

This is definitely the way forward when they can be found for a particular engine although even then a higher voltage when cranking will make a big difference

Why don't you tell us what the engine is and what the problem is you are trying to solve. As people keep telling you, but you keep ignoring - is that it's an odd thing to do and it feels like you are trying to fix the symptoms of an otherwise simple problem (such as a knackered starter or bad earth)

[Penelope Stopit]

Max_Torque said:

I know TVR owners like to mess around and modify their cars, but in this case i can;t see the point?

If your car doesn't start with a normal 12v battery and starter, the engine's f**ked. Fix the engine, don't modify the car to try to mask a failure!


All this extra wiring and contactors is likely to be a) highly unreliable and b) a massive fire risk when, inevitably, one relay gets a bit sticky, or contact welds on.....



Can you explain why you need 18V to start the engine??

This all started with me looking at starting circuits that are already in use but could be improved, I appreciate that many engines shouldn't need any extra help, this set-up is for one off modified engines with high compression and/or slow cranking problems caused by design not faults
You mention "fire risk" and I do agree that this is a big problem, I will need to take a closer look into the switching side of this and how to monitor the solenoids pulling in and dropping out so as to make them failsafe or possibly add a safety fuse
Thank you for your post

[Penelope Stopit]

eliot said:

Why don't you tell us what the engine is and what the problem is you are trying to solve. As people keep telling you, but you keep ignoring - is that it's an odd thing to do and it feels like you are trying to fix the symptoms of an otherwise simple problem (such as a knackered starter or bad earth)

Thank you, please see above

[eliot]

Penelope Stopit said:

Thank you, please see above

I'm out.

[Penelope Stopit]

eliot said:

I'm out.

I'm in

[anonymous-user]

Penelope Stopit said:

this set-up is for one off modified engines with high compression

I've built engines with CR's up to 15:1 (gasoline!) with super lightweight flywheels and cranks and not needed an 18v starting system yet.....

Penelope Stopit said:

and/or slow cranking problems caused by design not faults

a design that causes slow cranking is a design fault! fix the cause, don't bodge around the issue.

Penelope Stopit said:

You mention "fire risk" and I do agree that this is a big problem, I will need to take a closer look into the switching side of this and how to monitor the solenoids pulling in and dropping out so as to make them failsafe or possibly add a safety fuse

Contactors weld shut all the time, especially high current ones, you NEED a suitably rated fuse at the absolute minimum to prevent a catastrophic fire in that event

[Penelope Stopit]

Max_Torque said:

Penelope Stopit said:

this set-up is for one off modified engines with high compression

I've built engines with CR's up to 15:1 (gasoline!) with super lightweight flywheels and cranks and not needed an 18v starting system yet.....

Penelope Stopit said:

and/or slow cranking problems caused by design not faults

a design that causes slow cranking is a design fault! fix the cause, don't bodge around the issue.

Penelope Stopit said:

You mention "fire risk" and I do agree that this is a big problem, I will need to take a closer look into the switching side of this and how to monitor the solenoids pulling in and dropping out so as to make them failsafe or possibly add a safety fuse

Contactors weld shut all the time, especially high current ones, you NEED a suitably rated fuse at the absolute minimum to prevent a catastrophic fire in that event

Good observations. I have started so I'll finish and then look into its uses, I have already seen similar (12 volt/24 volt) discussed at motorsport and marine forums but didn't delve too deep into what engines and under what circumstances the higher voltage cranking was needed

I am working on safety at present and am almost there (maybe)

[Peanut Gallery]

This may well have already been done thought of, but..
Charging - you are aware you can't really just wire the batteries together in a simple charging system?
Voltage drop from extra cables, solenoids?

Personally I would think of a high discharge battery (I'm old school, lead acid is my limit!) Situated close to the starter with decent power and earth cables. Thinking about it a lithium battery?

(Minor note, when playing sound systems capacitors are not going to affect a starter motor)

Just my 2p worth!!

[tapkaJohnD]

Triumph Spitfires used a 6V ignition coil on a 12V system, by using a resistance lead to the coil for normal use to drop the volts to the coil, that was by passes for starting allegedly making cold starting easier. Just confusing, in my experience.

But you want to boost the starter
Could you put in an extra battery, in series, to give the starter 24V, but run the rest of the car off just one? No relays, or is that too simple? Recharging the battery not used by the car's systems, but onky the starter, could be acheived by some simple, low current, switching circuit.

John

[Penelope Stopit]

tapkaJohnD said:

Triumph Spitfires used a 6V ignition coil on a 12V system, by using a resistance lead to the coil for normal use to drop the volts to the coil, that was by passes for starting allegedly making cold starting easier. Just confusing, in my experience.

But you want to boost the starter
Could you put in an extra battery, in series, to give the starter 24V, but run the rest of the car off just one? No relays, or is that too simple? Recharging the battery not used by the car's systems, but onky the starter, could be acheived by some simple, low current, switching circuit.

John

The circuit that supplies 12 Volts to a 6 Volt coil during cranking as you probably know is called a ignition ballast resistor circuit and works very well in overcoming too lower a voltage at the coil during cranking, in addition to this it gives a higher voltage than needed to run the engine once it's fired yet this higher voltage gives a really good spark at the plugs for initial starting

What I am trying to achieve here is a better system than the 24 Volt system that already exists as I know 24 Volts is too harsh on a starter motor in everyday use, 24 Volts is ok for rally cars and the likes that aren't stopping and starting all the time everyday

Above you have unknowingly posted up the idea of a system that already exists and are amongst the good thinkers here at PH, just as Max_Torque has made a big good point about fire risk due to contacts welding. I have nearly cracked the 18 volt starting circuit and am also looking at reaching the same 18 volts with a simplified method that will be frowned upon by some. Can't please them all

Below is the circuit that you have thought up that already exists. Should you think of something else like this that doesn't exist you could earn millions, get thinking. Taken from http://www.texasindustrialelectric.com/relays_1119...

Edited by Penelope Stopit on Tuesday 18th July 10:31

[Penelope Stopit]

Finished the job at long last
I can't see anything wrong now but a second pair of eyes are always welcome