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Old 14-11-2022, 18:55   #1
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Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

Hi,
Did anyone modify the 115A Mitubishi alternator found on D1-4 Volvos for more amp delivery.
Mine are new and 2 engines and I want to avoid the costs of upgrading to a large case alternator and the D+ problems which creates further costs and install issues
with the volvos.

By looking at the 115A alternator, that delivers the first 20min around 80A and then scales down to 60A you should be able to modify this alternator with bigger diodes and rectrifer plus maybe relocate them away from the alternator. Like this you move heat away and it should be able to produce the 80-90A constantly. A 200A aftermarket alternator (but without temp control which is needed for lithium) direct replacement is available that done exactly this. The newer D2-50F already have serpentine belts that can deliver this 80-90A, it does in stock config for the first 20min.

That would be enough for me and worth the switch from DC2DC to this modified alternator plus Nordkyn VSR200 „regulator“ plus is all I would need. A mod like this should be 200-300Euro max versus a Balmar or alike that is 1600 minimum multiplied by 2 because it’s a cat.

Did anyone done something like this?
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Old 14-11-2022, 19:14   #2
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

It is the windings that glow red, then yellow and then fly to bits, not the diode pack. In many of the later model high output generators in automotive use, they actually water cooled then, well coolant cooled but you get the idea.
The air cooled higher output generators use at least two fans, some use three fans to move the heat, water moves 3 times the heat of air so ... maybe you can run some tubing through the gaps between the winding and the case and pump water through to carry away some of the heat to assist the air cooling.

For those that don't believe alternators overheat or it is exaggerated

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Old 14-11-2022, 19:37   #3
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

A more DIY approach - duct in air from a cooler ambient area using a bilge blower style of pump. Direct the pumped air directly onto / into the alternator.
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Old 14-11-2022, 22:53   #4
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

One of the best mods you can do is mount, the diode rectifier pack ( or build a new one ) and regulator externally and fan cool it separately. This removes considerable heat.

Additional fans can then mitigate the mechanical friction heat and winding I2R heat.
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Old 15-11-2022, 01:09   #5
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

Direct LFP charging is not possible with a fabricated Mitzi 115A alternator or a different brand. When you increase the engine above 1500 rpm, you can charge your LFP batteries with Mitzi 115A fabricated alternator with 115A current, but I don't think you can sustain it for more than 3-4 minutes. I'd say definitely not try it, as I'm sure it will have dangerous and costly consequences.

Details about the alternator modification and measurements I made with Mitzi 115A alternator and VP D1-30 engine can be read in the discussion topic which I've shared before. https://www.cruisersforum.com/forums...ry-269415.html

It is possible to turn the alternator on and off safely while working by controlling the rotor excitation energy. By adding a simple thermal limiter to this, you can solve the two main alternator problems with a $100 budget. I've been using this solution on my own boat for six months.

In this way, it is possible to charge LFP batteries with the highest power I can get from the alternator, without losing the alternator and using the existing infrastructure. How high this can be depends on how hot the alternator is at most.

I mounted a 90C thermostat on the most heated part of the alternator. The summary of the measurements I made with my Mitzi 115A alternator, which opens and closes in a controlled range of 90-80 C, is as follows:

Starting 115A.
Three minutes later it goes down to 90A.
One minute off to cool down to 80C.
90A for two minutes.
One minute off
.
.
.

At 90C maximum allowable operating conditions, the average continuous charging current of around 60A is acceptable.
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Old 15-11-2022, 01:29   #6
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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Originally Posted by goboatingnow View Post
One of the best mods you can do is mount, the diode rectifier pack ( or build a new one ) and regulator externally and fan cool it separately. This removes considerable heat.

Additional fans can then mitigate the mechanical friction heat and winding I2R heat.
that is what I meant, 50% of the heat generated of an alternator is done by the diode pack. If I move this away 80A constant should be possible from the 115A Mitzi.

Question is what do I need for diodes/rectifier pack, 2nd if you use oversized ones the heat generated is much lower.
What pack can I use to move it away and 2nd if this is possible with the Mitzi 115A?

The Nordkyn VSR200 does all the regulation without modifying via the sense lead wire and alternator can be switched on/off by the BMS. The Mitzi has an internal temp regulation from factory which is quite conservative protecting the alt but that is missing on most aftermarket replacement alternators, also the 200A upgraded one and the reason you cannot use it with the Nordkyn VSR200.
@solar support: that's inline with what I measured 60A constant. if you move 50% heat away=diode pack 80A constant should be possible to achieve. I don't even try to pull 115A as this heats the alt up significantly but limited to pulling 80A keeps it in the 90-100C temp range now for 20min unmodified, with diodes pack away that should work constant.
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Old 15-11-2022, 02:11   #7
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

By using a laser-operated thermometer, you can read precise measurements from different points of the alternator, which is overheating while working. I measured the temperature of the diodes of the alternator and the stator windings on the opposite side. These are visible through the ventilation grilles of the aluminum outer casing. The highest temperature is measured in the stator windings. When you think that the stator windings surround the entire alternator, it is necessary to consider that the biggest source of heat generated is the stator. The heat generated in the alternator can be reduced by taking diodes out of the alternator case but the great amount of heat generated in the alternator would stay.
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Old 15-11-2022, 02:31   #8
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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Originally Posted by SOLAR SUPPORT View Post
By using a laser-operated thermometer, you can read precise measurements from different points of the alternator, which is overheating while working. I measured the temperature of the diodes of the alternator and the stator windings on the opposite side. These are visible through the ventilation grilles of the aluminum outer casing. The highest temperature is measured in the stator windings. When you think that the stator windings surround the entire alternator, it is necessary to consider that the biggest source of heat generated is the stator. The heat generated in the alternator can be reduced by taking diodes out of the alternator case but the great amount of heat generated in the alternator would stay.
sure if you shoot 115A its windings are glowing fast. if you limit it to 80A it takes 15-20min till it's throttling down to 60A which tells me if I move the heat source diodes away the 80A should be possible constantly. I modified several alternators already, purely for car Hifi use and all shown a 25% increase in constant output by moving the diodes and rectrifer away and oversize the diodes. that's inline what I expect here too.
what you do is optimize cooling capability as less heat is generated inside the case that has to be moved away.
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Old 15-11-2022, 03:38   #9
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

Quit trying to make a generator from a sail drive. They rob the engine of HP. The alternator is designed to run the motor and a few accessories, not a house.
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Old 15-11-2022, 04:09   #10
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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Quit trying to make a generator from a sail drive. They rob the engine of HP. The alternator is designed to run the motor and a few accessories, not a house.
I have 2x50hp instead 2x20hp in my 7t 40ft Lavezzi, plenty of power...wot is 14kn, so I can easily sacrifice some 3-5hp.
Not making a Gen out of them,just optimize what I have to get max out. But I could, that option fallback.
I know that stock alt is 115A means 50% load constant which is 60A what I got. moving diodes away should give 75-80A constant.
Alt need to work when I motorsail, main charge source is solar.
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Old 15-11-2022, 05:23   #11
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

https://store.alternatorparts.com/qf...rectifier.aspx
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Old 15-11-2022, 06:27   #12
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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Quit trying to make a generator from a sail drive. They rob the engine of HP. The alternator is designed to run the motor and a few accessories, not a house.


An alternator is just a power supply really.
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Old 15-11-2022, 07:12   #13
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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Quit trying to make a generator from a sail drive. They rob the engine of HP. The alternator is designed to run the motor and a few accessories, not a house.
After the modification to turn the alternator on and off safely while it's running, you don't need anything but a simple switch to turn it on and off whenever you want.

If you have solar energy that easily fills your batteries, which are discharged by 50-70% at night, you rarely use this switch to start the alternator. You don't want the alternator to run, even if it's not necessary to fill the batteries, while motoring after lifting the anchor in a windless and sunny weather.

Turning off the alternator safely at any time prevents unnecessary wear of the alternator itself and its belt and saves fuel.
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Old 17-11-2022, 05:57   #14
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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After the modification to turn the alternator on and off safely while it's running, you don't need anything but a simple switch to turn it on and off whenever you want.

If you have solar energy that easily fills your batteries, which are discharged by 50-70% at night, you rarely use this switch to start the alternator. You don't want the alternator to run, even if it's not necessary to fill the batteries, while motoring after lifting the anchor in a windless and sunny weather.

Turning off the alternator safely at any time prevents unnecessary wear of the alternator itself and its belt and saves fuel.
Your mod is wrong strategy, overloading the alternator till it glows then switching it off till it cools down to some degree and repeat increase wear drastically and the AH output after 1 hour is much smaller then running it for 1h at its max continuous around 60A and starting around +25% for the first 15min.

That it takes 15min with 25% above and 40min with 15% continuous at startup tells me its not much heat that needed to be transferred away. So moving away the diodes (or just replacing them by oversized ones) should be enough heat reduction so it can run 80A continuous. If I raise Startup current to 95A it takes 5min to throttle massively down shows me that around 80A is what windings and stators with the its cooling capacity can continuously do on the 115A Mitzi.

And my 840AH soon 1100AH would discharge by around 10%(soon 5%) at anchor at night, during passage 20%(soon 15%). The 1100AH will be rarely 100% full as the bank is massively oversized and if then I have plenty means to burn excess energy from running the watermaker till washing cloth. At passage I want my bank as full as possible at any time, just for security reasons.

And yes I want my alternator to run every time I run the engine, especially during lifting or deploying the anchor or motoring with the max amount the alternator can deliver. The engine hour cost much more then any drop of less fuel saved and alternator and belt turn anyhow just under less load plus I am massively overpowered so can sacrifice the max 5hp anytime. A replacement 115A Mitzi overhauled cost 200 Euro, if that dies after 12 years instead 14 I am fine. will get one as backup part anyhow. With my 7t 40ft I sail mostly anyhow, good light wind capabilities so the engine runs only when there is really a propulsion need.

After 5 days without any solar charge at anchor, the seldom 2 times a year that happens I will charge via 170A shore power charger connect to a Honda EU20i gas gen, much more efficient then with the Diesel engine.
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Old 17-11-2022, 06:04   #15
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Re: Can you modify 115A Mitsubishi alternator with larger diodes or rectrifier

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You are sure that works with a Mitzi 115A, they have internal temp regulation.
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