Self starting generator without separate starter motor?

Thread Starter

brik2k

Joined Nov 18, 2011
4
Hi,
I'm hoping some of you can save me some time and explain why this is a bad idea. I have a 2kw pull start inverter generator that I'd like to convert to electric start. The obvious solution is to fit a separate starter motor kit and move on but where's the fun in that. Instead, I'm wondering why the generator side of generator/engine pair couldn't be temporarily repurposed into a starter motor to get the engine running before switching back to "generator mode".

At first glance, it would appear that the generator is similar to a brushless motor in that it has coils surrounded by rotating permanent magnets. I have not taken my generator apart to verify this so please correct me if you know otherwise. Anyway, that being the case, would it not be possible to use something like a VFD or an oversized brushless motor speed controller to drive the generator as a motor using a 12v battery? I realize it's likely more complicated than it sounds or otherwise you'd see self starting generators available for sale. Doe anyone have any insight as to why this isn't a thing? Cost, complexity, just won't work?

Thanks!
 

crutschow

Joined Mar 14, 2008
25,133
I believe the complexity and cost required to do that from scratch would far exceed the cost of a separate starter motor.
They can do it with hybrid cars since there already is high power electronic circuitry available.
 

BobTPH

Joined Jun 5, 2013
2,435
I believe the complexity and cost required to do that from scratch would far exceed the cost of a separate starter motor.
They can do it with hybrid cars since there already is high power electronic circuitry available.
Yep, I meant hybrid, not electric, of course.

Bob
 

MrSoftware

Joined Oct 29, 2013
1,824
I suspect the challenge is going to be in the control circuitry. The inverter controller is probably proprietary and I suspect you're going to have a difficult time figuring out how it works in detail, so that you can modify it. You could potentially brute force it by adding a secondary controller only for starting, that disconnects the original controller while it starting mode then re-connects it for generator mode, but again without understanding the existing controller this method would be fraught with risks.
 

jpanhalt

Joined Jan 18, 2008
9,790
Combined starter/genrators are not a new idea. Some old tractors used them. I had a Case 444 garden tractor with a 14 HP Kohler that did:

https://casecoltingersoll.com/showthread.php/23000-1974-Case-444-not-charging-Starter-generator-housing-getting-very-hot

https://www.amazon.com/DB-Electrical-GDR0002-Starter-Generator/dp/B019DHPP64

There are probably others. I sold mine a few years ago. Regret it, but needed the space. You could search for a wiring diagram for that series to get some ideas. Worked great and never had a problem for all the years my dad and I owned it.
 

shortbus

Joined Sep 30, 2009
7,768
Jpanhalt is right about a generator/starter, but a modern "generator", especially an inverter type is really an alternator not a generator. So is your "generator" something you're willing to kill and replace? By experimenting on it?

A gen/starter was a real generator, the difference is a generator has brushes and a commutator.
 

debe

Joined Sep 21, 2010
1,170
Yes they are a 3phase winding, but they are 350V AC on a 240 V machine. The 3 phase power is converted to DC then fed through a sine wave inverter. I doubt that 12V is going to cut it to drive the coils. The only way would be how Danfoss BD35 fridge compressors are run on 12-24V DC, is convert the 12V to a higher voltage (42V DC for the 3 phase compressor) for the generator it would need to be 300 V then use that to drive the windings. Probably not very practical. just an interesting concept.
 

Tonyr1084

Joined Sep 24, 2015
4,737
My dad told me when he was a young driver the cars he drove had a generator (not an alternator) to generate power to charge the battery. The generator was also used as a starter motor. By powering the generator it acted like a motor. Once the engine was running it became a generator. I know nothing of how it was set up - all I know is this is what my dad told me a long time ago.

Today I suspect that generators are far more complex than a simple DC motor turned into a generator. I have a DC motor on my bench with an LED connected to its leads. The motor is gear reduced, so spinning the reduced gear ends up spinning the motor with a lot more RPM. Enough to light the LED brightly. That motor constitutes a generator when spun, but is a motor because it spins when electrically powered.
 

MrSoftware

Joined Oct 29, 2013
1,824
They don't start the internal combustion motor with the alternator or the drive motor. They use a regular starter motor like any car.
Toyota hybrids (not sure about others) use one of the motor/generators to start the motor. I have a Prius and the combustion motor start is silent. One moment it's off, the next moment it's running, no traditional starter sound at all.
 

jpanhalt

Joined Jan 18, 2008
9,790
I don't know anything about a Prius, but an IC engine past TDC with fuel in a cylinder can be started with just a spark. It's one of the well recognized dangers of electronic ignitions that can give a spark when turned on and before they get a signal from the crankcase position sensor. That's a particular concern with model aircraft.

A big part of the noise you associate with starting is probably due to the "Bendix" engaging the flywheel. A different linkage, might not make that noise.
 

Reloadron

Joined Jan 15, 2015
5,512
Hi,
I'm hoping some of you can save me some time and explain why this is a bad idea. I have a 2kw pull start inverter generator that I'd like to convert to electric start. The obvious solution is to fit a separate starter motor kit and move on but where's the fun in that. Instead, I'm wondering why the generator side of generator/engine pair couldn't be temporarily repurposed into a starter motor to get the engine running before switching back to "generator mode".

At first glance, it would appear that the generator is similar to a brushless motor in that it has coils surrounded by rotating permanent magnets. I have not taken my generator apart to verify this so please correct me if you know otherwise. Anyway, that being the case, would it not be possible to use something like a VFD or an oversized brushless motor speed controller to drive the generator as a motor using a 12v battery? I realize it's likely more complicated than it sounds or otherwise you'd see self starting generators available for sale. Doe anyone have any insight as to why this isn't a thing? Cost, complexity, just won't work?

Thanks!
The concept of a starter generator has been around for years. I once had an old 10 KW (1950s vintage) Onan generator powered by a 4 cylinder flat head Waukesha gas engine. I was briefly involved with the Lear Siegler power equipment division and the manufacture of starter generators for jet turbine aircraft engines. Anyway, nothing new.

In your case you would need to get inside and see exactly what you have. Many of the newer Inverter Generators actually start with a alternator making AC which is rectified to DC and drives the inverter, some just start with a PM (Permanent Magnet) DC generator. Once you know what you have in detail it's a matter of using it to start the engine.

When all is said and done you look at cost and complexity and I don't see it as simple or inexpensive. If they make an electric start kit for it I would just buy it and be happy. A 2 KW unit should not require all that much starter and keep in mind, you go electric start you lose some portability with a battery and then there is a matter of maintaining the battery.

Ron
 

Poor old sod

Joined Jul 25, 2017
108
i'm disabled, and cannot pull over my 750w genset. if its a 3 phase one with 12 peripherial permanent magnets and 18 poles as shown in another article, then connecting a 12v240v 50Hz 150w inverter across one phase, and a start capacitor commoned to another phase to get direction surety should spin it slowly. A 2ah Li-ion bat can supply a burst of 15-20A to start it. batt will hold charge for months. on board recharge is easy. the cranking speed is abt right {50/18Hz.} the genset is wired delta, and the other 2 phases will get some power, but I won't use Pspice to work out exactly what happens. I may have to current limit the inverter output with a dimer control which auto ramps up to full power? I wish I knew how much power is needed to spin the dead unit. it's simlar load on the arm to a briggs and stratton 3.5hp, if that helps.
 
I had a Honda Civic hybrid.
The main electric motor serve the triple purpose of starting the combustion engine, providing additional boost when required, and functioning like a HV generator the rest of the time.

The car did not have a conventional 12V alternator. rather 12VDC would be derived from the main HV bus, which recharged a smallish lead-acid battery.
 

MrSoftware

Joined Oct 29, 2013
1,824
I had a Honda Civic hybrid.
The main electric motor serve the triple purpose of starting the combustion engine, providing additional boost when required, and functioning like a HV generator the rest of the time.

The car did not have a conventional 12V alternator. rather 12VDC would be derived from the main HV bus, which recharged a smallish lead-acid battery.
The Prius is similar. The 12v battery is tiny, almost like a lawn mower battery. It's just used to boot the electronics, and once the car is booted the 12v subsystem is powered by the main traction battery, I think the voltage varies by generation but is over 200VDC.
 
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