Smaller alternator for m113k
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
Smaller alternator for m113k
Hi,
I was wondering if any of you fine gentlemen happens to know the part.no of a 100amp-140amp alternator that would fit the M113k?
Thankful for any suggestions
Best
Jon
I was wondering if any of you fine gentlemen happens to know the part.no of a 100amp-140amp alternator that would fit the M113k?
Thankful for any suggestions
Best
Jon
MBWorld Fanatic!
Joined: Jun 2014
Posts: 1,036
Likes: 169
From: Portland, Oregon
2019 Jeep Trackhawk, 2002 CLK55, 2014 911 Carrera
I think the alternator off a 2002 CLK55 is in that range. The wiring on the back may be different, but I know it will bolt up and the belt fits fine.
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
My car (SL55) really isn't a street car anymore and the lightest race batteries don't really work with the 180amp alternator we have stock. Even the 150amp is too juicy.
I might eventually have to go the custom route and fab up some brackets for a suitable aftermarket alternator but if there is one that fits bolt on that would save me alot of time and effort sourcing parts.
MBWorld Fanatic!
Joined: Jun 2020
Posts: 2,138
Likes: 870
04 E55 AMG (totaled), 07 S550 4Matic, 14 E63S
I'll admit I have not built a race car but the amps refer to the MAX output. An alternator is voltage regulated. I wouldn't expect it to have any issues putting out a stable voltage, even if your battery was smaller than stock. Unless there is a minimum field current on the regulator that forces a minimum current output and that drives the voltage in your tiny battery way too high. What's actually happening that gives you concern?
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
I'll admit I have not built a race car but the amps refer to the MAX output. An alternator is voltage regulated. I wouldn't expect it to have any issues putting out a stable voltage, even if your battery was smaller than stock. Unless there is a minimum field current on the regulator that forces a minimum current output and that drives the voltage in your tiny battery way too high. What's actually happening that gives you concern?
The built in voltage regulator that comes in our cars is made to work with lead-acid batteries so unfortunately its no good for me in that regard. I know there are specific aftermarket voltage regulators for running Lithium batteries with alternators but i would like to keep the complexity down in the car and not change too much.
What also adds complexity is that the you can't really compare Lithium to Lead on an amp to amp basis since they don't have the exact same cranking output.
Last edited by Doomguy; Jul 7, 2022 at 12:16 PM.
MBWorld Fanatic!
Joined: Jun 2020
Posts: 2,138
Likes: 870
04 E55 AMG (totaled), 07 S550 4Matic, 14 E63S
If the Li-Ion battery is constructed for the correct resting voltage, it shouldn't pull too many amps from the alternator, particularly once it is charged. Lead acid batteries can charge at 100A or greater if they are really discharged. What are the specs of the Li-Ion battery? It is possible that the battery is really designed for applications with no charging system. If your Li-Ion battery is REALLY pulling too much current from your alternator, I have the following comments:
1) You are going to harm a smaller alternator
2) The battery is not designed for similar resting/charging voltages as a conventional lead acid. For example, a fully charged lead acid is around 12.7-12.8V. They will draw big current when discharged but once they are topped off, they won't draw too much even if they are receiving 13.5V or more. So you could be looking at harming the battery. The charge voltage is what matters here. The current will follow.
Can you link to the battery you are running?
1) You are going to harm a smaller alternator
2) The battery is not designed for similar resting/charging voltages as a conventional lead acid. For example, a fully charged lead acid is around 12.7-12.8V. They will draw big current when discharged but once they are topped off, they won't draw too much even if they are receiving 13.5V or more. So you could be looking at harming the battery. The charge voltage is what matters here. The current will follow.
Can you link to the battery you are running?
Trending Topics
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
The battery is the Swedish brand Topend which is very popular and well tested with the local people running track. As you say the Litiums are fine while fully charged but since I will be driving to and from the track that might cause issues with the charging.
They used to have batteries for road/track with a built in battery management system that would handle the stock charging but since most people went straight for the non-BMS race batteries they were discontinued.
The specs are as follows: 13 volt, 20 Ah ,550 Rca. Suitable alternator up to 140 A, charging current 14 - 14,5 volt. weight 4kg/8.8lb.
As far as I know the battery is strictly designed as a light weight racing battery.
Both your points are valid. Maybe the real culprit is the stock voltage regulator. I know that there can be major differences between brands of Li-Ion batteries when it comes to charging caracteristics, I just don't know enough abut the specifics of this battery to know all the whys when it comes to picking the correct size alternator for it. Im really only trying to stick to the vendors suggested alternator specs to keep out of trouble lol.
Its hard to match the weight of the Li-ion batteries but maybe some of you guys have other types of batteries that you are running with stock alternators and voltage regulators at a similar weight? I'm open to all suggestions.
They used to have batteries for road/track with a built in battery management system that would handle the stock charging but since most people went straight for the non-BMS race batteries they were discontinued.
The specs are as follows: 13 volt, 20 Ah ,550 Rca. Suitable alternator up to 140 A, charging current 14 - 14,5 volt. weight 4kg/8.8lb.
As far as I know the battery is strictly designed as a light weight racing battery.
Both your points are valid. Maybe the real culprit is the stock voltage regulator. I know that there can be major differences between brands of Li-Ion batteries when it comes to charging caracteristics, I just don't know enough abut the specifics of this battery to know all the whys when it comes to picking the correct size alternator for it. Im really only trying to stick to the vendors suggested alternator specs to keep out of trouble lol.
Its hard to match the weight of the Li-ion batteries but maybe some of you guys have other types of batteries that you are running with stock alternators and voltage regulators at a similar weight? I'm open to all suggestions.
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
MBWorld Fanatic!
Joined: Jun 2020
Posts: 2,138
Likes: 870
04 E55 AMG (totaled), 07 S550 4Matic, 14 E63S
If that battery is designed to be charged at 14-14.5 volts, then I don't have a clue why anyone is worried about the stock charging system. I can only think of one scenario:
- Your Li-Ion battery is depleted (perhaps from running at the strip with the alt disconnected for extra power - after all, if you are concerned about the weight of the battery, I presume you don't race with the alt charging). With a depleted Li-Ion, the theory could be that with an alternator that is capable of charging at more than 140A, you may end up dumping current into the battery too quickly and harm it (or worse).
Other than the depleted-battery theory above, I see NO reason at all to be worried about it. Just driving around you should be totally fine because 14V is roughly what the stock alternator puts out. If you don't believe me, get an inductive current probe and check the charging current. If the battery is mostly charged, it will probably pull under 5 amps, regardless of the max current rating of the alternator.
EE here, btw....not that I use it much these days. IMO, most Li-Ion chemistry should be used with a BMS. So the idea of "getting around" the need for a BMS by spec'ing a slightly lower output alternator is really dodging the issue. But do conduct the experiment I outlined and report results.
- Your Li-Ion battery is depleted (perhaps from running at the strip with the alt disconnected for extra power - after all, if you are concerned about the weight of the battery, I presume you don't race with the alt charging). With a depleted Li-Ion, the theory could be that with an alternator that is capable of charging at more than 140A, you may end up dumping current into the battery too quickly and harm it (or worse).
Other than the depleted-battery theory above, I see NO reason at all to be worried about it. Just driving around you should be totally fine because 14V is roughly what the stock alternator puts out. If you don't believe me, get an inductive current probe and check the charging current. If the battery is mostly charged, it will probably pull under 5 amps, regardless of the max current rating of the alternator.
EE here, btw....not that I use it much these days. IMO, most Li-Ion chemistry should be used with a BMS. So the idea of "getting around" the need for a BMS by spec'ing a slightly lower output alternator is really dodging the issue. But do conduct the experiment I outlined and report results.
Last edited by kevm14; Jul 7, 2022 at 02:40 PM.
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
If that battery is designed to be charged at 14-14.5 volts, then I don't have a clue why anyone is worried about the stock charging system. I can only think of one scenario:
- Your Li-Ion battery is depleted (perhaps from running at the strip with the alt disconnected for extra power - after all, if you are concerned about the weight of the battery, I presume you don't race with the alt charging). With a depleted Li-Ion, the theory could be that with an alternator that is capable of charging at more than 140A, you may end up dumping current into the battery too quickly and harm it (or worse).
Other than the depleted-battery theory above, I see NO reason at all to be worried about it. Just driving around you should be totally fine because 14V is roughly what the stock alternator puts out. If you don't believe me, get an inductive current probe and check the charging current. If the battery is mostly charged, it will probably pull under 5 amps, regardless of the max current rating of the alternator.
EE here, btw....not that I use it much these days. IMO, most Li-Ion chemistry should be used with a BMS. So the idea of "getting around" the need for a BMS by spec'ing a slightly lower output alternator is really dodging the issue. But do conduct the experiment I outlined and report results.
- Your Li-Ion battery is depleted (perhaps from running at the strip with the alt disconnected for extra power - after all, if you are concerned about the weight of the battery, I presume you don't race with the alt charging). With a depleted Li-Ion, the theory could be that with an alternator that is capable of charging at more than 140A, you may end up dumping current into the battery too quickly and harm it (or worse).
Other than the depleted-battery theory above, I see NO reason at all to be worried about it. Just driving around you should be totally fine because 14V is roughly what the stock alternator puts out. If you don't believe me, get an inductive current probe and check the charging current. If the battery is mostly charged, it will probably pull under 5 amps, regardless of the max current rating of the alternator.
EE here, btw....not that I use it much these days. IMO, most Li-Ion chemistry should be used with a BMS. So the idea of "getting around" the need for a BMS by spec'ing a slightly lower output alternator is really dodging the issue. But do conduct the experiment I outlined and report results.
My understanding is that the component to be worried about is really the alternator because of the low internal resistance of the li-ion battery itself they tend to force the alternator to deliver max current at very low rpm. Since they only have a fan to rely on for heat management they fry at low rpm and max output.
As to why the battery might be harmed as well I don't know...
MBWorld Fanatic!
Joined: Jun 2020
Posts: 2,138
Likes: 870
04 E55 AMG (totaled), 07 S550 4Matic, 14 E63S
It only matters if the battery is deeply discharged and therefore drawing a lot of current. Is the theory that a low output alternator somehow runs cooler than a high output one? I'd think they are both designed to run at max output. By the way, alternators will not put out their max at idle. They typically need to be spun quite a bit faster.
You measured the output? What was the current and voltage going into the battery then? And was it discharged or fairly topped off?
Even in a scenario where your battery was discharged for some reason, a 20Ah battery is going to charge quite quickly. So even if it did draw a ton of current it will not be for long. I still don't see what the issue is. You haven't proven anything is operating in a risky fashion.
Low internal resistance just impacts the rate of charge/discharge. If the battery is fully charged, it has no reason to draw big amps. And I stand by what I said above about a discharged 20Ah battery. This isn't a big deal unless I am missing something.
You measured the output? What was the current and voltage going into the battery then? And was it discharged or fairly topped off?
Even in a scenario where your battery was discharged for some reason, a 20Ah battery is going to charge quite quickly. So even if it did draw a ton of current it will not be for long. I still don't see what the issue is. You haven't proven anything is operating in a risky fashion.
Low internal resistance just impacts the rate of charge/discharge. If the battery is fully charged, it has no reason to draw big amps. And I stand by what I said above about a discharged 20Ah battery. This isn't a big deal unless I am missing something.
Last edited by kevm14; Jul 7, 2022 at 04:13 PM.
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
From what ive read that is one of the issues. The other being the Li-Ion batteries are very sensitive to the charging voltage output meaning the the rather crude voltage regulators in our cars would risk damaging them with fluctuating output.
It was some time ago and I can't remember how much the battery was charged but the alternator was giving around 14V if memory serves me correctly.
Maybe you are right and its fine to run the Topend Li-Ion batteries with a 180A alternator and the stock voltage regulator but it doesn't make any sense why they would so strongly advice against it. I was in contact with the guy and he said it would kill the battery. Why I don't know and I'm not here to provide any proof of concept neither.
If there is no alternator suitable for that battery type ill just look into to other types of light weight batteries but I still thought it would be worthwhile to look into what options we have for the M113k since other people also might be interested in downsizing or swapping alternators for other purposes.
It was some time ago and I can't remember how much the battery was charged but the alternator was giving around 14V if memory serves me correctly.
Maybe you are right and its fine to run the Topend Li-Ion batteries with a 180A alternator and the stock voltage regulator but it doesn't make any sense why they would so strongly advice against it. I was in contact with the guy and he said it would kill the battery. Why I don't know and I'm not here to provide any proof of concept neither.
If there is no alternator suitable for that battery type ill just look into to other types of light weight batteries but I still thought it would be worthwhile to look into what options we have for the M113k since other people also might be interested in downsizing or swapping alternators for other purposes.
MBWorld Fanatic!
Joined: Jun 2020
Posts: 2,138
Likes: 870
04 E55 AMG (totaled), 07 S550 4Matic, 14 E63S
I think it's a bit of nonsense. Ideally you would use a BMS to charge though. But if it's OK to connect directly to an automotive charging system, I really don't see a big difference between a 180A or 140A or 120A alternator from a battery perspective, except for the deeply discharged case I mentioned. And again that will not last very long because the battery will increase SoC rapidly. If your use case is to race with a Li-Ion battery and it mostly stays charged, I personally do not think you have ANYTHING at all to worry about with a 180A alt. Again, check the charging current going into the battery at hot idle and you will see that the battery doesn't take a lot of current. It has nothing to do with the alternator's max output rating.
What is the charging and discharging C rating of that battery? 1C charge/discharge means 20 amps for a 20Ah battery. If i is able to crank the M113K it must be able to put out in excess of 250A, maybe more, for brief periods.
What is the charging and discharging C rating of that battery? 1C charge/discharge means 20 amps for a 20Ah battery. If i is able to crank the M113K it must be able to put out in excess of 250A, maybe more, for brief periods.
Last edited by kevm14; Jul 7, 2022 at 05:13 PM.
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
I think it's a bit of nonsense. Ideally you would use a BMS to charge though. But if it's OK to connect directly to an automotive charging system, I really don't see a big difference between a 180A or 140A or 120A alternator from a battery perspective, except for the deeply discharged case I mentioned. And again that will not last very long because the battery will increase SoC rapidly. If your use case is to race with a Li-Ion battery and it mostly stays charged, I personally do not think you have ANYTHING at all to worry about with a 180A alt. Again, check the charging current going into the battery at hot idle and you will see that the battery doesn't take a lot of current. It has nothing to do with the alternator's max output rating.
What is the charging and discharging C rating of that battery? 1C charge/discharge means 20 amps for a 20Ah battery. If i is able to crank the M113K it must be able to put out in excess of 250A, maybe more, for brief periods.
What is the charging and discharging C rating of that battery? 1C charge/discharge means 20 amps for a 20Ah battery. If i is able to crank the M113K it must be able to put out in excess of 250A, maybe more, for brief periods.
I don't have the c-rating but according to the vendor it can take 2x the amps (40A) under short periods of time and 5x the amps (100A) under very short periods of time. Its rated at 550Rca. It has a built in cell balancing curcuit but not a full BMS.
I don't know for how long the alternator would put out max current at the track. The vendor did say that if only running it fully charged at the track with a circuit breaker a 20ah should be fine, it was more for the street he had concerns, presumably referring to the discharged theory you mentioned.
It seems that the easiest solution for this is either swapping batteries at the track or getting one with a full BMS for running both street and track.
MBWorld Fanatic!
Joined: Jun 2020
Posts: 2,138
Likes: 870
04 E55 AMG (totaled), 07 S550 4Matic, 14 E63S
Yes my recommendation would be that you can race with it with no issues with your stock alternator but for the street a regular battery would be a much better choice. A battery of small capacity like that will discharge pretty significantly when you aren't driving the car and then it will need to charge up, leading to a potential overcurrent situation. I still think going to a smaller alternator is really not the right solution, even then.
Thread Starter
Junior Member
Joined: May 2020
Posts: 18
Likes: 0
From: Sweden
SL55
Yes my recommendation would be that you can race with it with no issues with your stock alternator but for the street a regular battery would be a much better choice. A battery of small capacity like that will discharge pretty significantly when you aren't driving the car and then it will need to charge up, leading to a potential overcurrent situation. I still think going to a smaller alternator is really not the right solution, even then.
Thank you for taking the time to respond and for an interesting discussion.
