Can you damage your starter motor with too much current?

  • #1
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Hey all!

Today I took my car to the shop for some starter issues. They told me that the starter had been damaged by a battery with a higher CCA rating than was safe for the starter motor and it burned out my motor slowly over time. I feel like they may be BS'ing me, but I'm not sure.

I know my battery is ~12V. The one I had installed was rated to 880CCA and they recommend 330CCA for my car. From some research my starter motor has an impedance of about .02-.04 ohms, and car batteries should be around the same. So that gives me a total impedance of about .06 ohms. Taking V=IR I should be able to pull a maximum of about 200 Amps on startup. I assume that a higher CCA battery has lower resistance, so let's just take that out of the picture entirely. Assuming a maximum current draw for my starter, the most I should possibly see is about 400Amps which is not too far above the 330CCA recommended for my car. I would imagine that they would design the starter to be able to handle at least 400 for short periods of time (I.E. the 2 seconds it takes to start my car).

I would like to know if anyone else has any experience or insight with this issue. I'm definitely getting the starter replaced because it's straight up dead, but I would rather not get a new battery if I don't have to.

Thanks!
 

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  • #3
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I feel like they may be BS'ing me
This...
 
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  • #4
Averagesupernova
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I wouldn't take anything back to that shop.
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BTW, do they sell batteries?
 
  • #5
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BTW, do they sell batteries?

They probably do, I told them not to touch the battery beyond what they needed to swap the starter. It was the dealership (and after seeing the bill I'm never taking it back there anyway)
 
  • #6
Averagesupernova
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Interesting that one of the links in post #2 has the same problem with the same lame answer from a dealership. Ugh...
 
  • #7
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Interesting that one of the links in post #2 has the same problem with the same lame answer from a dealership. Ugh...

Agreed, I have a good mechanic, but since I moved he's 80 miles away.... Still might be worth it to take my stuff to him though cause he always charges a fair price and has never tried to lie to me
 
  • #8
Averagesupernova
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Agreed, I have a good mechanic, but since I moved he's 80 miles away.... Still might be worth it to take my stuff to him though cause he always charges a fair price and has never tried to lie to me
That can be priceless.
 
  • #9
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Maybe you already know this but just my two cents of reafirmation

Well the reality is quite simple and you can surely remember this and tell i to anyone you know and has had a similar question.

as long as the battery is rated for 12 volts it really doesn't matter how much amps or amphours it has, it can be a big one or a small one - doesn't matter.

your starter motor has a fixed impedance when its turning and it's coils have a fixed ohmic resistance by default , so at say 12 volts it can only consume a fixed amount of current under load, so as long as you don't change the voltage nothing else changes, it is the same starter motor turning the same engine for which it was designed and having the same impedance/resistance.

and it doesn't matter that a bigger "better" more stronger battery might supply a larger current due to lower internal resistance in the battery, as long as it's 12 volts the amount of current a load can take is determined only by the voltage and the resistance of the load.





surely if your starter motor for some reasons stalls or has some other problem, a bigger more capable battery might burn it down faster but that is not the point because even a specified battery that is healthy will generate enough current for the period of time necessary to produce damage to coils insulation in a damaged starter motor if the conditions are met such that it can happen.

the only real reason I would not suggest putting an oversized battery in a car is simply because its more expensive and has no real benefit, for example I'm using a small gasoline engine and it only needs a 52Ah battery so why would I buy a more expensive bigger unit if i'm okay with a small one, but the bigger unit would be just as fine
 
  • #10
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That's some good insight Girts, thanks!

My initial concern when I was at the dealership was because I was under the impression that the battery was normally the current limiting factor of the starter system. After my initial research it became clear that was not the case. And it makes a lot of sense why my old starter got progressively worse over a short period of time. It started with the occasional click no start that would turn over on the second try, and progressed to needing to try about 20-30 times before it would turn over. So in that 20-30 tries that was 20-40 seconds of stalled out current flow through the motor (Which was probably not so great for it cause all the energy went to heat instead of mechanical energy)

Fortunately I didn't buy that battery, it was in the car when I bought it.
 
  • #11
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sounds a familiar problem, I highly doubt your starter did not turn because it was stalled because if hat was the case every time you would turn the ignition to start position your lights would flicker and get dimmed and after some 40 times of doing so your battery would be much emptier and our lights would go down much more, I assume that was not the case.

usually what happens is the starter has a smaller tubular "thingy" located right next to the larger tubular shaped metal cone in which the very DC motor is located in. the smaller cylindrical unit is what is called the solenoid because quite literally it has a coil and a metal rod inside the coil which forms a solenoid.
the function of this solenoid is twofold, firstly as you turn the ignition key to start position it engages two contacts that send power to the solenoid and that makes a B field in the solenoid which pushes the metal rod outwards, that metal rod is connected to your starter motor gear teeth and at that moment the starter motor gear teeth are pushed into position with the large gear ring position on your flywheel in order so that it could turn the engine.

now the other very important function the solenoid does it is essentially a large relay, at the other end of the rod while being pushed engages two large contacts which connect the large +12V wire coming from your battery, as those contacts are engaged the +12v can now flow into the starter motor itself and start to turn it, the ground connection is usually made through the starter motor chassis. So it works as a relay in order so that big wiring wouldn't have to go through your front panel and ignition key.



now what usually happens is with age and wear the solenoid and mechanical moving parts get dirt and dust inside them and sometimes rust so they get slower or get stuck altogether so the starter doesn't push out its gear and doesn't connect the contacts, or simply the contacts erode away and it becomes hard to engage the starter motor because of eroded and dirty contacts, 12v is a rather small voltage so it is hard to overcome dirt and burnt contacts in order to get a low enough resistance for current to pass.



I don't know what type of car you have but beware sometimes the problem is not the starter but say battery contacts themselves or other parts.
I once had a situation where my lights were working but my starter would not turn, at first I thought it was the starter as I took it off I concluded it was okay so only then I realized that one of my battery connection contacts was dirty and oxidized, it could pass enough current for lights but not enough for the starter needs, as I cleaned it everything worked just fine.
So you need to be careful before starting to do big and time consuming jobs as sometimes all that is needed is a clever thought and 5 minutes of small cleaning.
 
  • #12
Maybe you already know this but just my two cents of reafirmation

Well the reality is quite simple and you can surely remember this and tell i to anyone you know and has had a similar question.

as long as the battery is rated for 12 volts it really doesn't matter how much amps or amphours it has, it can be a big one or a small one - doesn't matter.

your starter motor has a fixed impedance when its turning and it's coils have a fixed ohmic resistance by default , so at say 12 volts it can only consume a fixed amount of current under load, so as long as you don't change the voltage nothing else changes, it is the same starter motor turning the same engine for which it was designed and having the same impedance/resistance.

and it doesn't matter that a bigger "better" more stronger battery might supply a larger current due to lower internal resistance in the battery, as long as it's 12 volts the amount of current a load can take is determined only by the voltage and the resistance of the load.





surely if your starter motor for some reasons stalls or has some other problem, a bigger more capable battery might burn it down faster but that is not the point because even a specified battery that is healthy will generate enough current for the period of time necessary to produce damage to coils insulation in a damaged starter motor if the conditions are met such that it can happen.

the only real reason I would not suggest putting an oversized battery in a car is simply because its more expensive and has no real benefit, for example I'm using a small gasoline engine and it only needs a 52Ah battery so why would I buy a more expensive bigger unit if i'm okay with a small one, but the bigger unit would be just as fine
An oversized battery is not really a problem as you say, it's just more expensive and it might not even physically fit in the car. A lot of cars don't have a ton of room in the engine compartment these days.
 
  • #13
Baluncore
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Without load, a DC starter motor will spin at a rate proportional to voltage. That is because the spinning motor generates a proportional back EMF that opposes the applied battery voltage. The voltage across the starter is therefore the battery voltage less the back EMF due to rotation.

Motor torque is proportional to motor current. The starter motor speed will therefore balance the torque and RPM.
Torque is proportional to current, I = ( (Battery EMF ) – ( Back EMF ) ) / Rstarter.

Above a sufficient battery capacity, the capacity will be quite irrelevant.

Problems occur when the motor does not spin and the full voltage appears across the starter = stall torque. That high current overheats the motor windings. But why does it happen? Is the motor locked by thick cold oil, is it a hydraulic lock due to water in the cylinder, or is the vehicle in high gear with the clutch engaged? Only under that stalled fault condition, can continued use of the starter, with a high capacitance battery, damage a starter motor.
 
  • #14
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Baluncore, everything you say is correct but I think that the situation in which the starter motor would be stalled and with an applied voltage to it at the same time is very rare, because in order for that to happen the relay contacts must be engaged which means the gear is already pushed out and so the solenoid is likely fine, as you said either the engine has to be stalled itself or the gearbox, but even then a typical starter motor is rather powerful and trying to turn it several times would result in some clinging noises and small bangs from gears as they usually have little movement between them.

judging by how the OP described the situation it sounds more like a faulty starter solenoid not engaging the main contacts.
But that's just my opinion being half the world away so the only real way of knowing os for either the OP himself or a good mechanic to physically check and disassemble the unit if necessary
 
  • #15
Baluncore
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I think that the situation in which the starter motor would be stalled and with an applied voltage to it at the same time is very rare,
I agree. But in general, the only situation where battery capacity could damage a starter motor is when an incompetent operator tries repeatedly to start the engine while another pre-existing fault condition exists. It is possible, an unlikely situation, but it will happen somewhere, sometimes.

Starter operation advice is usually along the lines of;
1. If it stalls and does not turn the motor, switch it off immediately. Check the battery terminals. Find and fix the problem.
2. If it turns the engine, never operate the starter for more than 15 seconds, then wait a whole minute for it to cool.
 
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  • #16
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It started with the occasional click no start that would turn over on the second try, and progressed to needing to try about 20-30 times
These symptoms are what I'd expect if motor brushes have worn down to where practically no contact pressure remains, or the starter relay contacts are shot (image of typical damage courtesy of a Google image search).
tart-switch-turned-422644d1327607175-e430-starting-issue-engages-but-stops-3starter-solenoid-int.jpg


The one I had installed was rated to 880CCA and they recommend 330CCA for my car.
Does it get very cold where you are? What make/model car? Gas or diesel engine?

My 6 cylinder, 4.3L truck's seven year old battery gave it's all several weeks ago, and is why I have the specs at hand. It uses a size group 75 battery which is available in the range of 690 to 700 CCA for top end products (3 year full replacement warranty, with several vendors offering 5 year warranties with the final 2 years pro-rated), 650 CCA for mid-range (2 year warranty), 540 to 550 CCA in the 'economy' or 'value' range (1 year warranty) with prices averaging from $138 to $120 to $100 USD for these three ranges. Given daily operation (or nearly so; infrequent charging encourages sulfation) battery life tracks well with CCA rating.

880 CCA is a fairly high rating by comparison, but is probably in the ballpark for an 8 cylinder gas engine, and necessary to get a high compression diesel engine turning. CCA (Cold Cranking Amps) is specified at 0°F, and CA (Cranking Amps) at 32°F with the ratio between them approximately 1.25:1 (for wet cell batteries - AGM batteries are a different sort of beast). Available cranking current falls with temperature; operation in extreme climates is another reason why a higher CCA-rated battery may be preferred.
I feel like they may be BS'ing me
Yep, chalk me down with the others here - what you've been fed is mostly BS. However, provided that battery 'A' can source more current than battery 'B' it will leave a bigger mark. If the motor is seized hard, for example, no amount of starter torque is going to make it turn, but a higher-rated battery allows the possibility of a greater degree of incidental damage (overheated and burned out starter windings, splashed contacts, etc) if current remains below what is necessary to take out the fusible link.

Study the current and voltage scope traces from the second link in @CWatters post #2.

Provided the engine and starter are in good condition, current should fall nearly immediately to what is necessary to crank the engine, and terminal voltage will return to a range that allows proper spark plug operation (10.5 volts is the minimum terminal voltage allowed for CCA and CA ratings). Terminal voltage doesn't fall off as much on a high CCA rated battery versus a lower rated one, and is more capable of delivering sparks hot enough to ensure ignition. Here, voltage crashed to 9V during the first few milliseconds, hit about 10V after the first engine revolution, and went above 10.5V within the next two revolutions.

Cranking Amps & Volts.jpg


I've never had to spin a modern fuel-injected gas engine more than a half dozen revolutions before it fired up, but on cold days carburated engines tended to be cranky. The rule of thumb was to wait several minutes after the third successive start attempt before trying again. This gave enough time for a (potentially) flooded carb to clear, and self-heating from the unsuccessful attempts to warm the battery electrolyte, and bring terminal voltage high enough to allow ignition.
 

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  • #17
jim hardy
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my old starter got progressively worse over a short period of time. It started with the occasional click no start that would turn over on the second try, and progressed to needing to try about 20-30 times before it would turn over. So in that 20-30 tries that was 20-40 seconds of stalled out current flow through the motor (Which was probably not so great for it cause all the energy went to heat instead of mechanical energy)


That click-but-not-engage is a common symptom on Toyota starters. There are some crucial clearances in the mechanism that engages those big contacts shown in @Asymptotic 's post.
Had full current actually made it through your starter it would have spun.

Most starters are "series wound" . A Series woundDC motor that has no mechanical load will overspeed.
For that reason some manufacturers add a small shunt field winding to limit speed.
Others only apply voltage to the starter after its drive gear has engaged the flywheel.
I don't know which Toyota does but i suspect the latter .
Once i encountered an Opel Kadet that had neither of those features . The starter drive gear failed to engage so the starter motor oversped and slung its armature wires out of their slots , wrecking it of course.

old jim
 
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  • #18
Without load, a DC starter motor will spin at a rate proportional to voltage. That is because the spinning motor generates a proportional back EMF that opposes the applied battery voltage. The voltage across the starter is therefore the battery voltage less the back EMF due to rotation.

Motor torque is proportional to motor current. The starter motor speed will therefore balance the torque and RPM.
Torque is proportional to current, I = ( (Battery EMF ) – ( Back EMF ) ) / Rstarter.

Above a sufficient battery capacity, the capacity will be quite irrelevant.

Problems occur when the motor does not spin and the full voltage appears across the starter = stall torque. That high current overheats the motor windings. But why does it happen? Is the motor locked by thick cold oil, is it a hydraulic lock due to water in the cylinder, or is the vehicle in high gear with the clutch engaged? Only under that stalled fault condition, can continued use of the starter, with a high capacitance battery, damage a starter motor.
This is true, but a starter motor in a car is turning an engine that has compression in it. That presents a significant load to the motor. While not stalled, cranking a starter motor too long under such a load as a typical engine will damage the starter. Furthermore, any corrosion on the starter contacts will cause 'hot spots' that will further erode the contacts, worsening the condition.

A larger battery solves none of these problems in starter motors.
 
  • #19
Averagesupernova
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The reason a starter motor will be damaged if one tries to crank the engine for too long is because the starter is designed-down to the point that it will survive the typical couple of seconds needed to start an engine but not several minutes. A starter could be designed and built for continuous duty but it would be many times larger, much more costly, and pointless.
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Series wound, shunt or PM, or a combination of doesn't matter. There are many machines out there rated for continuous duty that have any one of those winding configurations to suit a particular job
 
  • #20
Baluncore
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A larger battery solves none of these problems in starter motors.
But some people work out of their vehicles, they need a larger capacity battery that will run a stereo system, an electric refrigerator, a two way radio and a cordless-tool battery-charger, all without the need to add a dual battery system to an already crowded space.
 
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  • #21
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This question pops up all the time in various forms, whether it's car batteries as here, or USB chargers or ... many other things. I've worked out an answer that people seem to understand. Spoiler alert - what follows is a massive amount of over-simplification and total disregard for the fundamentals of elec eng (power), but *it doesn't matter* for this explanation.

So, taking this post's example, say I have a car with a healthy starting system, e.g. no seized bearings in the starter motor, no fuses replaced by lengths of coat-hanger wire etc. The only problem I have is a dead battery. To solve that problem I have two options - a battery rated at 12V, 330CCA and a nice RC, the original manufacturer's specs. And I also happen to have a personal nuclear power station which runs a few fair-sized cities. One of the outputs from the power station's turbine generator happens to be a handy 12V DC outlet on the wall.

It's an 8GW power station so at its rated voltage of 22KV it can deliver a total accumulated current output of about 360,000 amps.

At the 12V outlet it can therefore deliver 667 million amps, if you disconnect the city first. (elec eng's, physicists and frustrated pedants who are screaming at their computers "He's comparing/confusing AC and DC and watts and VA and .... I'm going apoplectic!!" calm down. It doesn't matter. This is to help a lay person grasp the difference between power (specifically current at a given voltage) delivery capability of the supply and power (current) draw by the consuming device. It's not meant as part of an ElecEng doctoral thesis).

OK, moving along. You drive (or tow because you have a flat battery, remember?) your car into the power station and connect the starter motor to the 12V DC, 667 mega amp outlet and turn the key. It will start just fine. The fact that the wall outlet can deliver 667,000,000/330 = 2 million times more current than your auto parts shop battery is capable of is totally, and I mean totally, irrelevant.

The wall outlet will say to your starter motor "I can give you twelve volts and up to six hundred and sixty seven million amps. Because I'm a regular kind of guy, I'll guarantee you the 12 volts (and BTW up to 14.4 and a tad over is still fine for you, but I'll give you 12), but it's up to you to draw the current you need/want."
And the starter motor replies: "12 volts is good for me and I'll take 140 amps, thanks very much."

And they lived happily ever after.

The only difference between your $150 car battery and the $50B power station is that the station will be able to run your starter motor indefinitely. OK, two differences - it also takes up more space than a car battery.

And as others have noted, because a car starter motor is designed to handle the stresses of say a 3 or 4 second burst, say 10 times a day, for say 15 years, your starter motor connected to the power station will likely die within ... pick a number ... 10 minutes. But its death will have nothing at all to do with the fact that it's connected to a nuclear power station.

Don't forget to reconnect the cities after you've started your car.
 
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  • #22
sophiecentaur
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your starter motor has a fixed impedance when its turning and it's coils have a fixed ohmic resistance by default , so at say 12 volts it can only consume a fixed amount of current under load, so as long as you don't change the voltage nothing else changes, it is the same starter motor turning the same engine for which it was designed and having the same impedance/resistance.

Car batteries and starter motors are a bit like irresistible forces and immoveable objects - it's anyone's guess what can happen.

The Impedance of the motor will depend upon the rotation rate and the mechanical load. Starter motors are not designed for constant running but they are designed (to a price) to run for much longer than normally needed to start the engine (well within the envelope of parameters of the particular car). The cubic capacity and compression ratio etc. affects the mechanical power demanded from the motor. There will always be a dip in battery volts whilst the motor is running. It's possible that the beefier the battery, the less of a dip - which will mean more current flowing. I can understand the mechanic's reaction to the fault, even though I / we don't actually agree with his theory.

I had an experience, many years ago which may have been relevant to the OP's experience. My ex wife started the car and the pinion stuck in the starter gear. The engine was running with the starter engaged and that caused so much current through the starter that the windings just melted. I just wonder if a late release of the pinion could have caused your problem of excess current. It's a long time ago and I don't remember if the battery took too much of a knock for it to survive the experience.
 

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