# Car battery STARTER voltage help (not charger) using variety of methods (possibly AC)

Status
Not open for further replies.

#### kingtal0n

##### Junior Member level 3
Hello,

In the stores now we can buy such car battery voltage boosters as low as $20-$50
However they go bad over time. I want to learn how 'they' work, and find other methods to do the same thing.
So I can replace and maintain the system for years without buying magic boxes

There are no rules to this circuit complexity. I Don't mind generating AC with a hand or foot(bike)-crank through a rectifier feeding a series of capacitors to generate the electrical boost necessary to help an already mostly good battery. I have no idea if that would work (but I hope it would because its on my list to figure out)

My car has the battery in the rear, and a long "0" gauge cable to the starter. So it does start fine with a new battery, but the starting is slow as the sudden voltage drop at the starter creates a sort of 'lag' where the motor initially turns very slow and then speeds up. My goal is to remove this lag/delay by boosting voltage either at the battery or at the starter.

I have already considered the use of capacitors near the starter, and I think this is a very simple solution. Turn key, charge caps, start engine, disable caps. However I do not know how much capacitor I will need or if this is even a 'smart' idea.

Another idea is to use capacitors with a small "step up" from ebay, which takes 12v and turns it into say 16v. that way the capacitors which maybe a little too small get an extra bit of juice. 16v quickly becomes 10v when you turn the key, know what I am saying? It wouldn't sit that high for long. Right now I hit the key and 12.6v turns to 7.8v at the computer. So it must be 7v~ at the starter or less. Alot of current and very low voltage. Not good.

Another idea is to use some kind of oscillator with a coil or inductor to store energy in a magnetic field, coupled to capacitors, transistors, that stuff all together I know from looking at various curcuits could be used to boost voltage. Its beyond me technically but I am trying to work that direction anyways so this would be a good opportunity to try and salvage a used transformer or something and put it to work here.

So thats basically it for now: hand/foot crank idea, AC current oscillator + inductors&transistors&regulators, capacitors, caps + step-up booster, thats where I am at. Oh that and just buying a bigger battery lol

##### Super Moderator
Staff member
There are the less expensive 'car battery boosters' which plug in to the cigarette lighter, and which no doubt are rechargeable batteries. I imagine they are over 16VDC, so they can quickly push a few A into a borderline car battery. It may not sound like enough to do much, but I have seen cars start after a few minutes charging at just a few Amps, that would not start beforehand.

It may simply be due to the warming effect of several Amperes going through the battery. You may have seen advice to run the headlights in a cold car for a minute, just so it warms the battery a bit and raises its voltage output so it has an easier time cranking the engine. Thus it gains more Watts than it loses to run the headlights.

The idea is that the booster pack supplements power to a half-good battery, to get the engine running, then leave the booster pack plugged in for a while to recharge to 15 or 16V. The batteries decline with time and use.

Of course these small-scale tricks cannot do much for a drained battery.

You can try to store juice in a gang of capacitors but it will require massive capacitors to store enough Ampere-seconds to help in cranking an engine.

It may help more to clean (by sanding, scraping, etc.) all connecting surfaces from the battery to the starter. Including the ground cable. A starter can draw several hundred Amperes. It's important to eliminate resistance in the connections. At 300 Amperes, a mere 1/100 ohm robs 3V.
You can use a voltmeter to measure the drop across a bolt and washer. Since you should not run the starter excessively, it might take ingenuity to attach a load where a voltage drop occurs so you can measure it.

#### kingtal0n

##### Junior Member level 3
My battery is brand new and fully charged. A charger isn't going to do anything for me,

not looking for a recharge here. Looking for a voltage boost at the starter during cranking. It might help just to get some at the solenoid.
See the ignition switch in a car typically runs through the key cylinder. And my fuse box is removed from the engine bay, its been relocated to the rear along with battery. So now there is more length everywhere of wires. It is custom situation and using large wires with good batteries just isn't quite enough to get away with it.

The next thing I am going to do (try) is remove the circuit from the ignition switch and create a separate relay for the starter solenoid. Just to see what that does for cranking first before trying to supplement the actual electric motor part with a boost.

#### KlausST

##### Super Moderator
Staff member
Hi,

It seems you don't have an idea about the current drawn at starting an engine.
This you should do first. Ask at your car garage. Or do an internet search..

Klaus

#### FvM

##### Super Moderator
Staff member
Seriously I don't get of which kind of boosting you are talking.

Is it about bosting the voltage for the starter or the ignition system? Boosting the starter voltage would require large super capacitors connected directly to the high current battery/starter circuit. A fresh battery gonna be much cheaper. Things may look different if you live in an arctic region, but hardly in Florida.

Boosting the ignition system supply during cold crank may be helpful for a badly designed car, a modern car provides sufficient ignition energy as long as the starter is still able to drive the motor.

#### kingtal0n

##### Junior Member level 3
Imagine a 2000 horsepower car but you don't want to carry 180lbs SLA battery necessary to crank 13:1compression Cold E85 540cid V8 engine.
So use a small battery 45lbs, and a booster when cranking.

If you are at home and have plug in power 220v, a charger on 'start' and try to crank an engine. But if the battery is dead it usually has nothing.
So the start feature is just a boost, not much current after all it comes through a 13amp wall fuse at 220v... and converts I suspect higher than 12.6v (never checked but it just occurred to me I could take one of those apart) there must be a step down transformer... I just think how much better would AC power be for doing all this.
If it could be done with magnetic field reactive i component all the crispier

thanks for reading, I did dig up old posts

Your other option is a boost switch mode supply with voltage and current feedback.

------------

If your 6V supply is capable of delivering 25AMPS - that is 150 Watts
Power = Volts X Current

if you boost the said voltage to 12V, assuming 100% efficiency! the current available will only be 12.5AMPS.
In practice it is possible to get a voltage converter of ~95% efficient at a specified load,$, though more common efficiency would be 50-60% for less$

-------
LM358 is a rather poor switch mode driver due to it's slow slew rate of 0.5 V/us. The best way to overcome it's limitations (if you can't afford a real switch mode controller or faster OP like TL084) is to reduce the switching frequency and increase the inductance respectively. Simply design it for continuous conduction mode with moderate (30 to 50%) current ripple. To avoid excessive capacitances, transistor and diode shouldn't be oversized.

--------
so this isn't an unresearched question

It isn't a question of design. Yes the battery should be larger and thats the problem solved. However the real question here is budget. BIG batteries are expensive. If a small cheap battery can be used in conjunction with small cheap electronics then I can avoid buying the proper huge battery for a looong time (forever?) or at least until the car no longer sits for weeks. I've noticed two things that seem to shorten an automotive battery is sitting, and big drains. Like when an engine fails to start on the first try. Or cranks for extended periods. I think that cranking time should be minimized especially for first cold starts, just instinctively I want to make it fire up as fast as lightning. Like fire comes out the instant you turn the key. Thats why I want to zap the starter lol
Sometimes it tries to fire on the first compression stroke, but the engine is moving so slowly the flame forces it the opposite direction and the engine slows Wayyy down or even spins backwards. Even with the timing ~6* btdc. I might try negative cranking timing

Last edited:

#### betwixt

##### Super Moderator
Staff member
Failure to start at first engine rotation is probably more to do with fuel reaching the cylinders than cranking power.
FYI, cranking a cold engine (even a warm one) can use several hundred Amps which equates to several Kilowatts of power, the very reason Lead-Acid batteries were chosen in the first place was their ability to deliver high current for short times. To attempt to mimic them using electronics is futile, you still need to get the power from somewhere and store it for long periods. Aside from batteries, the only electronic component that can do that is a capacitor but if you think a bigger battery is expensive wait 'til you see the costs of 12V 'thousands of Farads' capacitors in comparison.

The idea of generating power by hand or foot is also a non-starter. To give you some idea of the effort needed, tests were done here for a TV show recently to show how much energy a typical home uses. I appreciate the problem is slightly different but the test was to demonstrate the equivalent human power to that from a regular electrical source. If I scale the problem to your application, to double the battery power would be equivalent to a pro-cyclist uphill racing for about 20 hours, and that would only give enough energy for about 2 seconds of cranking!

The next thing I am going to do (try) is remove the circuit from the ignition switch and create a separate relay for the starter solenoid. Just to see what that does for cranking first before trying to supplement the actual electric motor part with a boost
That just makes thing more complicated. The solenoid IS the relay that connects the starter across the battery. If the ignition switch was to do it alone, it would be far too big and need the heavy cables fed all the way to the dashboard. The switch connects 12V to the solenoid coil which creates the magnetic field to pull the heavy duty starter motor switch. You gain nothing by adding more relays in a chain.

Brian.

#### FvM

##### Super Moderator
Staff member
The term booster seems to refer to using the existing battery, not an external supply. At least no external supply is mentioned in your original post, or does "possibly AC" refer to it?. Without external supply you are talking about a temporary energy storage device, charged by the original battery and sourcing e.g. 100 or 200A for a few seconds. Don't have much to add to the comment in my previous post. You really should get an idea about the energy density of available storage options. Super capacitor or a battery with sufficient current delivery, nothing else. Under circumstances, a smaller Li-Ion battery instead of a regular lead-acid device.

A technically simple solution that could help to spin up the engine would be a decompression valve as it's present at older diesel engines. Unfortunately not provided by car engines.

#### kingtal0n

##### Junior Member level 3
.....the only electronic component that can do that is a capacitor but if you think a bigger battery is expensive wait 'til you see the costs of 12V 'thousands of Farads' capacitors in comparison.
At school I have access to some pretty decently sized capacitors. I'll go see what they are rated for...

That just makes thing more complicated. The solenoid IS the relay that connects the starter across the battery. If the ignition switch was to do it alone, it would be far too big and need the heavy cables fed all the way to the dashboard. The switch connects 12V to the solenoid coil which creates the magnetic field to pull the heavy duty starter motor switch. You gain nothing by adding more relays in a chain.

Brian.
One of the biggest issues with older cars is the durability of the factory ignition switch. A common failure point is burnt up ignition switch due to the high current a starter solenoid pulls apparently. And in my application it is made worse with extra length wires. I have no doubt that adding a dedicated relay to supply current for starter solenoid (Which suggested is also a relay) will alleviate the pain experienced by factory ignition switch internals, and it may have a positive influence on cranking speed but that waits to be tested.

basically I guess i just need to take apart a jump box. Whatevers inside those things I need the best design of with the option to plug it into 220v AC and take it with me places
or something in the car itself that boosts electrical charge. I keep thinking I want to store energy in a magnetic field

Last edited:

#### betwixt

##### Super Moderator
Staff member
I have no doubt that adding a dedicated relay to supply current for starter solenoid (Which suggested is also a relay) will alleviate the pain experienced by factory ignition switch internals, and it may have a positive influence on cranking speed but that waits to be tested.
You are confusing the current paths. Cranking speed is decided by the power available to turn the starter motor and the load imposed on it by the engine. It has nothing whatsoever to do with the solenoid or ignition switch. The solenoid IS the relay, mounted near the battery and starter motor to reduce losses in the wiring while passing large currents. The solenoid coil is low power and can therefore be powered via the ignition switch along less cumbersome cables. The current along the battery-solenoid-starter motor-battery path is quite independent of the ignition switch so there is no point in trying to improve it.

If you want instant sure-fire starting I would look for solutions elsewhere, maybe pre-heating and/or pressurizing the fuel supply so it is available for instant use in the cylinders to lessen the time it takes to reach them.

Brian.

#### kingtal0n

##### Junior Member level 3
You are confusing the current paths. Cranking speed is decided by the power available to turn the starter motor and the load imposed on it by the engine. It has nothing whatsoever to do with the solenoid or ignition switch. The solenoid IS the relay, mounted near the battery and starter motor to reduce losses in the wiring while passing large currents. The solenoid coil is low power and can therefore be powered via the ignition switch along less cumbersome cables. The current along the battery-solenoid-starter motor-battery path is quite independent of the ignition switch so there is no point in trying to improve it.

If you want instant sure-fire starting I would look for solutions elsewhere, maybe pre-heating and/or pressurizing the fuel supply so it is available for instant use in the cylinders to lessen the time it takes to reach them.

Brian.
I can tell the ignition switch uses a higher current than you realize because the wire is enormous compared to other wires in the car, and because of all the burnt up ignition switches I've seen over the last 20 years.
The engine is tuned to inject a pre-cranking pulse (using an aftermarket computer), just enough fuel to fire it on the first stroke. The factory lets the motor spin for a second before injecting fuel to build up cranking speed but I hate that so I tune it out.

The issue is getting enough cranking RPM within the first second to actually fire the engine. When the motor turns slowly, it leaks compression due to the large camshaft and the first event fails to provide ignition at low frequency (60-120rpm). Or even spins the engine backwards.

I've got some video of cranking the motor through the ignition switch.
I've rewired the entire car and adding an external supply for solenoid starter coil was always in the plans, because I know the current kills the ignition switch already from all the other cars I owned.

I know it might not help but it needs to be done because I don't trust the OEM ignition switch to *not* burn up lol

#### betwixt

##### Super Moderator
Staff member
Burned out ignition switches is almost unheard of. What model of car is this?

Brian.

##### Super Moderator
Staff member
Burned out ignition switches is almost unheard of. What model of car is this?

Brian.
Probably a vehicle so heavily modified along with a starter motor solenoid that draws more current than the ignition switch is rated for.

Given that 0 gauge copper cables run about 0.1 mOhm and they probably have maybe at most 20ft of it to reach the trunk (assuming frame grounding) they have about 2 mOhm resistance in the wire. Even if they have a stalled starter (@~600A) they would only get a 1.2V drop. A typical starter motor in even high performance high compression engines shouldn't draw much more than 250A (0.5V drop) if even that high. Just look at any major high performance car site's discussion board this topic comes up a lot and members with heavily modified engines regularly comment on their 14:1 compression ratio engines starting with <200A.

I suspect, as it appears the OP has been doing the modifications themselves, they probably upgraded the engine with all the after market cams, high compression pistons, modified computer, etc but neglected to invest in replacing their starter motor with an aftermarket high torque starter (i.e. has reduction gearing to increase torque). I suspect the existing starter is running upwards of 500+Amps when cranking. This is indicative of a near stalling condition given the descriptions by the OP of the engine running backwards when it fails to start and the need for a "fresh" battery (old batteries lose CCA). Increasing the voltage (and current) will just shorten the life of this anemic starter.

I suggest you look over this google search list and buy a new starter motor.
https://www.google.com/search?q=high+torque+starter+motor instead of trying to add a voltage boost circuit (which I doubt will work out long term).
Also invest in a AGM battery they are much better at dealing with large CCA requirements and deep discharge.

#### c_mitra

Failure to start at first engine rotation is probably more to do with fuel reaching the cylinders than cranking power.
I guess there are two possible reasons: low temp (cold, long night) and weak battery. Typical lead batteries drop their voltage when cool.

Yes, modern starters take lots of current to start. But before the self-starters came, all cars were started with a crank that was turned manually. I am told that women hated it.

If the voltage is little low, the starter gets nasty. So if you can manage to raise the voltage to 13V or so (from around 10 or 11 if too cold) for about 1-2 secs, you are in luck.

The engine also becomes grumpy at low temp; perhaps the lubrication is to blame? But it only needs a little push- not a big kick!!

Perhaps a dozen Li-batteries in series parallel to raise the voltage by 3-6 volts for 2-5 seconds. Then they should fall back into charging mode.

They shoudl be cheaper than the capacitors- I mean the super capacitors.

#### ZASto

One thing that no one took in consideration is that a small battery cannot deliver high currents for starting cold "high performance" engine. By quoted I mean the gas guzzlers that could be found in US (IMHO 99% of them in Europe would not be street legal).
You can not BOOST the max current that your tiny (45 lbs) battery can deliver. Find some data on Lead Acid Batteries, how they behave under high load, ...

Take some time for reading/educating yourself at: https://batteryuniversity.com/

##### Super Moderator
Staff member
As you describe it, the long run of cable results in a voltage drop to the starter. In theory you can use a charge-pump voltage doubler (Dickson doubler).

Sequence of steps:

1) Switch the capacitor so it charges from the battery for a few seconds.

2) Switch the capacitor so its voltage is added (in series) to battery voltage.

3) The starter receives 15V at first, giving it a jolt. Output voltage declines quickly as the capacitor discharges within a few seconds.

The screenshot is a 10 second timeframe. The capacitor charges for 4 seconds. Then the switches are thrown so the capacitor discharges for 6 seconds to the load (1/20 ohm).
The switches can be relays or transistors or mosfets. They need to carry hundreds of Amperes. It's important for the switches to be activated at the same instant. If operated in the wrong sequence then it can create a short circuit through the capacitor.

Although the solenoid can have thinner (0 gauge) wire going to it (since it requires less current), the cable providing full current to the starter should be 000 or 0000 gauge.

- - - Updated - - -

The 100 Farad capacitor is really a gang of capacitors. Since they carry hundreds of Amps, they need to be the equivalent of 000 or 0000 gauge.

#### kripacharya

##### Banned
I saw a comment by ads-ee post #13 above, which amongst other things mentioned "...an aftermarket high torque starter..".

This IMHO sounds like the most elegant and likely solution.

#### kingtal0n

##### Junior Member level 3
I will try to get to everything...
This isn't about my setup. I am not looking for a solution to my 'problem'
I am looking for learning how electronics work knowledge that will assist in the future with more difficult problems.

Right now, for this current example project, I am just using a 20 year old factory engine and have tried a factory starter. Now I have a high quality aftermarket starter on the factory engine.

And not just any engine. Its a low compression, 150,000 miles truck engine that spins so easy you can almost breath on it.
The rings are 20 years old, its got almost no grab, I can turn the engine by hand from the main drive belt.

So this thing is not a bitch to turn at all. A factory starter is more than adequate. And I am using a nice one, after having tried the factory unit and wondered whether it was not just old/aged.

In fact, the way the engine starts is nearly adequate. Normal people can't tell there is any 'delay' or anything dumb happening. It starts like a 'normal' engine should, more or less. Because its so easy to turn, I've used an 18AH $32 ebay battery to start and run it for a year without issue. However. In a performance sense, i.e. the voltage signal when cranking, the initial rate of the engine rotation, leaves much to be desired. There is a low rate of change of engine speed when the voltage in the system drops. The battery is inadequate to move the engine "quickly" through all that length of cable. It did better with the smaller 18AH battery in the front than with 550CCA "group 24" lead acid in the rear with 0 gauge welding cable. I specifically tell the computer to inject a prime pulse. The factory does not use this method but I do because its the only way to get the motor to fire instantly every single time. However, because of the voltage-delay the engine turns very slowly at first, and if the piston is near TDC the spark happens too soon for such a slow rotating RPM and the engine either pings/knocks or chokes and spins backwards. The solution is going to be a combination of even further reduced timing, and getting the starter to spin the motor more quickly in the initial first half a second to one second of cranking. On to the solutions: I think the capacitor solutions are ideal for a variety of reasons, but I can't use anything unreliable in automotive sense. I'll buffer the solenoid's circuit first because its easy and simple and very low requirements for current to begin with so a little will go a long way. And if that does absolutely nothing I won't be surprised. And then I will move on to the large start current carrying wire and begin considering such things as$50 100farad super-capacitors run some special ways. It just has to be fool proof. Like was pointed out, I can't risk a cap discharging into a ground suddenly. I think the caps themselves are reliable its just the relays/switching with high current that I don't like. Most of my relays are 50-60amp max. I was thinking of using a pair of 60 amp relays to drive something with a capacitor, so I could shut them off when not in use (does that even mattter?)>
Another thing I am curious about is inductors, I keep mentioning this because I am hoping to do something with it. Why can't I store a bunch of energy into a magnetic field then let the field push voltage up for an instant during initial cranking.

#### ZASto

18Ah battery is inadequate for cranking truck engines. Due to internal resistance and ion buildup during high amp surge when internal resistance rises even more, the voltage drop on the battery cells is high, i.e the battery voltage is not high enough for cranking big engine.

##### Super Moderator
Staff member
It seems from looking at ebay that your cheapo SLA battery is for UPS or similar lower current applications, which translates to high internal resistance and low amperage for a starter motor situation. I highly doubt your battery is capable of supplying a 75A-100A for a starter motor application.

Whatever circuit you make it won't be the voltage that maters, but the maximum current it can output for that initial cracking of the engine, which is where all that 100A is used for, and as it is now your current limit is probably the battery itself. Whatever you do it will have to be done in parallel with the battery (which is how those battery boosters work) as the circuit needs to supply more current than the battery can supply. Your initial current pulse will need to be >75A and at least a couple of seconds long.

All of this matches your symptoms of the engine turning over slowly at first and then speeding up, which would be due to the lack of current, since your inrush current is severely limited with that not for starter applications battery. That situation of the TDC spark at the start of engine rotation causing the backwards turning engine is due to the lack of torque due to the lack of current (lack of current==lack of magnetic field==lack of torque). Also to start a car engine probably use more than half the 18Ah capacity in one startup, which translates to an abusive usage environment and increased sulfation causing failure far quicker than normal.

- - - Updated - - -

18Ah battery is inadequate for cranking truck engines.
Probably enough to crank over a 2 stroke manual lawn mower engine

Status
Not open for further replies.