do lithium batteries kill starter motors? (& brushed motors)

[jimmyhackers]

306 gti6

i had to recently replace my starter motor....6 monthsish after fitting a new lightweight lithium car battery.

can a lithium battery shorten a starter motors lifespan?

anyone had experience with this?


My reasoning: my RC car upgrading from years ago.

it was a brushed motor with 8v nicad batt.....was fine
i went to a 2s lipo/lithium battery @ 8.4v....brushed motor died within 2 or three use sessions
every replacement brushed motor afterwards.....same story 2 or 3 uses. (some were from 12v drills etc)

went to brushless setup (still going strong)

i worry as there are plenty of other brushed motors in my car.... and would rather they didn't burn up

TIA

Jim

[simon_harris]

not quite the same but airsoft motors are most often bushed and we use lipo's with them all the time without problems

[LunarOne]

I can't see how the chemistry of the battery would make a difference. Externally the battery will cause a voltage that will drive a current. Perhaps the Lithium batteries can deliver much more current than was the case before?

[davek_964]

Plenty of cars run with Lithium batteries from new - I own one. They don't cause starter motors to fail.

[stevieturbo]

LunarOne said:

I can't see how the chemistry of the battery would make a difference. Externally the battery will cause a voltage that will drive a current. Perhaps the Lithium batteries can deliver much more current than was the case before?

But current draw will be dictated by the load from the starter, which should not change ?

Definitely a strange one though

I've never used a Lithium on a car, nor really had any desire to.

[paralla]

The internal resistance of a lithium battery is significantly less than a lead acid battery so the current in the starter motor will be higher than if it was connected to a lead acid battery. The lower internal resistance causes less voltage drop across the battery leading to higher voltage at the starter motor.

The lower internal resistance of lithium also facilitates a faster ramp rate of current through the motor brushes and rotor windings putting additional demands on the brushes in particular. Increased arcing burns brushes.

[littleredrooster]

paralla said:

...so the current in the starter motor will be higher than if it was connected to a lead acid battery...

V=I/R, so unless the resistance changes, the current draw will be exactly the same. Also, the voltage is slightly higher (8.4/8.0) so current should be lower, not higher if anything.

paralla said:

The lower internal resistance of lithium also facilitates a faster ramp rate of current through the motor brushes and rotor windings putting additional demands on the brushes in particular. Increased arcing burns brushes.

Possible, and a slightly higher voltage according to the OP

[paralla]

littleredrooster said:

paralla said:

...so the current in the starter motor will be higher than if it was connected to a lead acid battery...

V=I/R, so unless the resistance changes, the current draw will be exactly the same. Also, the voltage is slightly higher (8.4/8.0) so current should be lower, not higher if anything.

paralla said:

The lower internal resistance of lithium also facilitates a faster ramp rate of current through the motor brushes and rotor windings putting additional demands on the brushes in particular. Increased arcing burns brushes.

Possible, and a slightly higher voltage according to the OP

You are thinking of just the resistance of the starter motor but the battery internal resistance must also be taken into account since it’s also in the circuit.

[Richard-D]

littleredrooster said:

paralla said:

...so the current in the starter motor will be higher than if it was connected to a lead acid battery...

V=I/R, so unless the resistance changes, the current draw will be exactly the same. Also, the voltage is slightly higher (8.4/8.0) so current should be lower, not higher if anything.

paralla said:

The lower internal resistance of lithium also facilitates a faster ramp rate of current through the motor brushes and rotor windings putting additional demands on the brushes in particular. Increased arcing burns brushes.

Possible, and a slightly higher voltage according to the OP

I don't think you've understood that equation you've quoted. It proves the exact opposite of what you're saying.

How can the current possibly be the same if you increase the voltage and you've kept the resistance the same? 'I' has to increase so that the new (higher) 'V' is achieved.

[ashenfie]

Maybe. I have seen that alternators can over because of the lower resistance and higher current flow. The same maybe true of starter motors.

[paralla]

When the starter motor is turning there are three things in the circuit.

1. The battery
2. The solenoid
3. The starter motor

The resistance of the starter motor and solenoid remain the same regardless of which battery is used.

When you change the battery from lead acid to lithium, the resistance of the battery is vastly lower therefore the current in the circuit is higher.

Edited by paralla on Wednesday 10th June 20:37

[littleredrooster]

I'll bow to the knowledge of my electrical friends, then, and stick to my ancient Mech Eng degree I always thought, however, that the reason for changing 6V systems to 12V was to decrease the current in the circuits and enable the use of lighter cable gauges. I've obviously applied this incorrectly to the OP's question.

[LunarOne]

The way I see it - if you have an unlimited consumer of current like a motor (especially a stalled motor) then given the same total resistance, higher voltage will result in more current flow. And if you drop the resistance in the circuit by using a battery with a lower internal resistance, then the consumer of current will be able to draw even more current and therefore generate more power. And if you exceed the power rating for the motor, it might burn out.

But it's been 35 years since I studied electronics at A-level!

[jimmyhackers]

paralla said:

The internal resistance of a lithium battery is significantly less than a lead acid battery so the current in the starter motor will be higher than if it was connected to a lead acid battery. The lower internal resistance causes less voltage drop across the battery leading to higher voltage at the starter motor.

The lower internal resistance of lithium also facilitates a faster ramp rate of current through the motor brushes and rotor windings putting additional demands on the brushes in particular. Increased arcing burns brushes.

this is the answer, thanks paralla.

my car is 28 years old now and im unsure if the failed starter motor was the original one. looked pretty old.....so unsure if the new battery install timing was just coincidence.

it had always been slow to crank, it sped up a fair bit after i cleaned all the earth terminals.
but eventually slowed down again.
a new 20ah lithium batt made it speed up a bit again
but again, it eventually got slower and started to stall the starter motor (activating the lithium batts bms shut off)
i exchanged the batt for a lithium 40ah one, and it cranked slow for about a week
after a week id get the same stater motor stall or sometimes it would just crank once then stall

on removal of the starter motor, the failure was the solenoid positive terminal had become loose/wobbly. i haven't dissected it to see what happened inside yet.

new starter motor sounds...."fierce" in comparison, no hesitation/lag, cranks once or twice at speed before the engine fires right up and purrs like a kitten

as paralla said....im noticing far less voltage drop across my battery on cranking. this higher voltage is applicable to everything inside my car.

i will effect everything to varying degrees i think, i have noticed....

my passenger side electric window switches have failed (both mine and the passengers)....upon dissasembly i noticed the drivers side window electrical switch inside the mechansims are a lot beefier than the passenger ones (annoyingly) the passenger switches are also opaque plastic and there is visible carbon arc burns/soot in them

i guess ill just have to see how she goes

thanks again