Too much power. How do i burn excess generation?

[ThatDane]

Hey everyone,

     I'm by far an amature with electronics. I've been pondering a problem I've had for years and many other people do too. I have a motor with a rotor and a stator that generate power for ignition and ~12v battery charging and provides 12 amps current max. The solution by the manufacturer is to use a maintainable battery and let it boil and refill it. If I run the engine at operating rpms with a full battery for like 3-5 minutes the regulator rectifier allows the voltage to climb to 14v if I continue it will climb higher to 16+v. The regulator rectifier is ok it's just not a sink, and if it doesn't have anything to do withe excess current, the voltage climbs. Letting the battery boil seems a like an outdated approach in this day. I've convinced myself that the proper solution is to make a load that will start to sink that excess current at around 13.8v and continue to do so until the charge voltage/current goes back down. I don't think this will prevent the battery from charging if it needs the juice, as I understand it will suck down all that 12 amps until its voltage rises to about 13.8v where the electromagical device will kick in and start eating that excess power. Im thinking this can be more of a parallel circuit than a something that needs to be in series.


I don't know where to start with something like this. The device (for a safety margin) would, i guess, need to be able to burn 500 or so watts off constantly without catching fire. The physical size isn't all that important I'd guess it could be as big as a 2000 watt inverter and that would be ok.

Any thoughts anyone?

[Bratster]

If the regulator is letting the voltage from your generator climb above 14 volts then it's faulty. Or doesn't actually have a regulator.

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[amyk]

If the regulator is letting the voltage from your generator climb above 14 volts then it's faulty. Or doesn't actually have a regulator.

This. Unless it's not a wound-field generator (instead using permanent magnets), it is relatively trivial to control its output by reducing (or PWM'ing, as early mechanical regulators did) the field current.

[james_s]

What happens if you let it go open circuit, or run it into a modest load, say 10-20 Watts and disconnect it from the battery? I think that's what I'd look into first, have a relay that disconnects the charging circuit from the battery and connects it to a power resistor to keep the output from spiking way up, if that is even necessary to do. If you put a heavy load on the output of the generator it will place a correspondingly heavy mechanical load on the engine driving it. When you figure in the various losses, 500W electrical load could easily suck up 1hp from the engine which I assume is performing other work besides driving the generator?

You can probably even find a voltage regulator meant for a motorcycle or outboard motor that will work without modification.

[james_s]

This. Unless it's not a wound-field generator (instead using permanent magnets), it is relatively trivial to control its output by reducing (or PWM'ing, as early mechanical regulators did) the field current.

From the post I'm assuming it is just that, a permanent magnet generator. I've seen them on riding lawnmowers, motorcycles and outboards, they're just a wound stator with a permanent magnet rotor. I've never looked closely at the regulator for one but they are typically regulated.

[ThatDane]

It is a pm generator. Its output can't be controlled its an antique outboard. To vregs available so their job well until there is no sink for the current. Its a small boat so ther isn't much in the way of accessories. Bow and stern lights are led . there is a 200 watt stereo but I'm not one to blare the music at max output.

I saw the post about the digital variable load for power supply testing but at 5amp max draw I'm thinking I'll just smoke it.

[Rerouter]

Try running the generator open circuit, that will tell you the max voltage you can expect,

From that size up a small load to keep that voltage below about 30V, (personally I cannot see it getting this high in a static state), and use a relay to switch the generator open circuit from the battery, as the relays can generally handle at least a 32V arc, you should be fine.

[Nusa]

The OP is right, this is nothing new. A lot of older small and mid-sized outboards had a battery charging system that consisted merely of a rectifier to convert to DC. No voltage regulator at all, other than the battery. Also known as an unregulated charging circuit. A significant portion of the output would be used by the ignition itself, but the battery had to absorb the surplus. The traditional solution for observed high voltage was to turn on the running lights, which of course is far more effective when they're incandescent rather than LED. Otherwise, most devices of the motors vintage, particularly marine or automotive devices, tolerated a few extra volts.

No model or brand was mentioned, but in some cases there are aftermarket  regulated rectifiers that include a voltage regulator that fit the original footprint and harness. They cost more, of course.

In the meantime, in this age of more sensitive electronic devices, I'd suggest running anything really valuable on an isolated electrical system with its own battery that you make a point of charging as required.

[ThatDane]

Nailed it. I have a cdi electronics reg rec on already. Its a '77 johnson 140. All of the electricals have been replaced as a pm . new   stator, new power pack, new plug coils, etc... All cdi parts. I have the 12amp stator rather than the 6 or so amp one that is usual. The info from CDI states that the reg rec needs to be attached to fla maintainable batteries . so they can boil once full.

My idea for a circuit to do this with was some fets and power resistors that could be signaled by a simple mcu to switch on and sink the excess current. Open circuiting (disconnecting the battery) from what I understand will smoke my charging system. As will allowing the voltage/current to climb too high for too long.

Another thing I've thought of is using some 100watt leds as sort of a sink . but i think that adds unnecessary complication. I'd like to make it more automatic so that when my brother or buddy borrow the boat, I don't have to trust that they will keep an eye on it.
 

[mzzj]

Cheapo solar panel charge controller could be pretty close what you need. 

No experience of these but specs look like it could work:
https://www.ebay.com/itm/30A-AMP-PWM-PV-Solar-Charge-Controller-W-USB-12Volt-Solar-Panel-Battery-RV-Boat-/273418474748

[ThatDane]

That looks pretty cool but what does it do when output exceeds demand? Does it open the charge circuit? Does it dump to a dummy load? Also, this is a start battery too. That looks like an inline thing, would drawing the 200 or so amps through it to crank the motor be possible?

[mikerj]

Is is a single or three phase PM alternator?  You can probably use a standard shunt regulator from a motorcycle in either case - the small capacity bikes are typicaly single phase and the larger bikes are three phase.

[ThatDane]

I think single phase.

http://www.cdielectronics.com/product/stators/johnson-evinrude-stator-173-2099-replaces-581303-581680-581860-582099/

Above is a link to the installed part. I'm guessing two outputs and two triggers.  I looked at this instructable

https://www.google.com/amp/www.instructables.com/id/How-to-make-a-reliable-motorcycle-voltage-regulato/%3famp_page=true

It looks like it shunts excess voltage to ground which if memory serves in this application would fry my stator windings and is why I passed on it.

Maybe a zener to drive a transistor to turn on a relay hooked up to a few 50 watt bulbs?

[james_s]

A shunt regulator doesn't just short the output to ground, it presents a variable load as needed, which sounds like exactly what you want.

Another idea is to use a buck regulator that can handle the maximum open circuit voltage the stator can produce. As the voltage goes up, the current it draws will actually go down. You will get a regulated output voltage while simultaneously reducing the mechanical load on the engine.

[Zero999]

Yes, a TL431, a couple of transistors, a big power resistor and a massive heatsink. This one should regulate at about 13.8V, which is a reasonable float voltage for most 12V sealed lead acid batteries. It will be fine up to above 10A. If more current is required, repeat Q2 and R4. Higher currents than 20A, will probably need a Darlington pair for Q1.

Rs just represents the wiring resistance and is not a physical component.

[Bratster]

Cheapo solar panel charge controller could be pretty close what you need. 

No experience of these but specs look like it could work:
https://www.ebay.com/itm/30A-AMP-PWM-PV-Solar-Charge-Controller-W-USB-12Volt-Solar-Panel-Battery-RV-Boat-/273418474748

That's an interesting idea. It would get wired with your generator output connected to the solar input.
And your battery connected to the battery connection.

you wouldn't touch any of the high current wiring, that would still come right off of the battery for your starter Etc.

When the battery gets charged up to 14 volts or so the controller would just stop passing power from the generator through to the battery.

not that much different from a solar panel, the 12-volt ones will go up to around 21 volts if there's no load on them and they have full sun.

you need to find out what the maximum open circuit voltage is from your generator to make sure that it won't fry the charge controller.

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[Ian.M]

Put a Peltier coolbox on board with a voltage sensitive relay set to 14V!

[Nusa]

Nailed it. I have a cdi electronics reg rec on already. Its a '77 johnson 140.

If the voltage climbs past about 14.5V, I would say the regulator portion of the device is no longer working. Some overcharging is to be expected, but max voltage shouldn't keep climbing.

[mmagin]

A motorcycle I had about 15 years ago had a 3 phase permanent magnet alternator, followed by a 3 phase bridge rectifier and a shunt regulator.  So at least with permanent magnet alternators, it seems like that's the reasonable thing.  Only real concern is having sufficient heatsink on the transistor

[ThatDane]

This is the reg/rec

http://www.cdielectronics.com/product/rectifiers-regulators/johnson-evinrude-regulated-rectifer-193-3408-replaces-580795-581603-582307-582399-583408-18-5708-9-17200-9-17200-9-17200-9-17200-9-17200/

. If the voltage is the same on the battery and the engine, but is over 15.5 volts at 4500 RPM, replace the battery with a
known good high quality MARINE FLOODED CELL battery.
4. A continued high voltage reading may indicate a problem in the stator.

This is the condition I face. Upon speaking to them they say the reg is designed to maintain stable voltage as long as the battery is good and an fla style. It wont work with agm or gel because they don't boil at full charge when excess power is being made.

This is the reason for needing a sink. I think a simple 13v zener to a transistor to a relay to some incandescent lights would help sap the excess. Maybe a small can of oil and a cooler and a thick coil of nicr wire in the oil bath to burn the power off..

[Ian.M]

You can buy adjustable voltage sensitive relays for 12V systems off-the-shelf from RV/caravan suppliers or chandlers (or EBAY).  Get one, and before you install it, use an adjustable bench PSU to set the cut-in voltage to the max you want the battery to ever charge to, and the dropout voltage at about 13.5V so the dump load doesn't drain the battery at idle or with the engine off, then install it and hook up a suitable dump load.

Start off with 50W 12V halogen bulbs as they are cheap.  When you've found out how many amps you need to dump to keep the voltage under the threshold, you can find something more useful to dump power into.  As I suggested earlier a 12V coolbox is a good dump load that will typically draw somewhere between 4A and 8A.   Refrigeration on a small boat used in the summer is always useful, and you can switch most of the thermoelectric ones to keep stuff hot in the winter.

[ThatDane]

Ok . I've been looking at adjustable voltage relays. I like the idea of these. And I do have a few( 60 watt tec's laying around that I could cobble into a cooler top.

I'm just having trouble actually finding some those adjustable relays that seems to be up to the task of living on a boat. The ones I'm finding all seem be some sort of a panel mount deal for solar appliacations. I'm finding auto shutoff relays for over and under volt for boats and RV's but no luck with adjustable ones. Anyone have any pointers on specific search terms I can use to try and get a seaworthy unit?

[Ian.M]

I'm *cheap* when it comes to boating gear but its *GOT* to be reliable.  If I'm paying a premium price I expect much higher quality than is often the case, as paying the 'marine' premium without getting commercial vessel grade quality is far far too common.

Get or build a bare board one then de-flux and conformal coat it, protecting the multi-turn preset screws with a dab of wax or latex, and masking off the terminal blocks.  Once its set up for the right voltage, seal the adjusting screws with a dab of nail varnish.

Put it in an IP65 rated small electrical box with good cable glands and a drain/vent at the lowest corner, mount it in a locker or other semi-sheltered location so  it doesn't get hit by 'green' water breaking over the boat, and thinly coat all wire ends with silicone dielectric grease before tightening the terminals on them to inhibit corrosion at the joints.    If you use an IP66 or better enclosure  because you don't have a suitable sheltered location it needs a Goretex vent for pressure equalisation instead of a drain/vent

This looks like a reasonable EBAY candidate for a bare board one - use it to pilot a heaver relay if your load's inductive or over 5A.
https://www.ebay.com/itm/12V-Mini-Battery-Automatic-Charging-Controller-Module-Protection-Relay-Board-/273008117098

Its got a NE555 for the voltage sensing, so it may not be too happy if the supply voltage goes over 16V.  However if its doing its job that should never happen and if it does fail its an easy and cheap fix or we could help you design a replacement that protects the 555 against over-voltage

[Gregg]

I have a friend that has a country home off grid and has a water impulse turbine driving a permanent magnet converted automotive style alternator [3 phase] with built in diode bridge.  It produces 17 amps at 27 volts continuously and charges a large battery bank that powers a 3KW inverter.  The excess power is dumped to several large resistors and is controlled by a Xantrex regulator http://www.xantrex.com/power-products/power-accessories/c-series-pwm-charge-controller.aspx
It has worked very well for the last 15 years and the heat produced keeps things from freezing in winter when nobody is around. 
As long as you have a dry place to mount such a device in your boat, it should fit your purpose, but it may not be marine rated if that matters to you.

[mikerj]

A shunt regulator doesn't just short the output to ground, it presents a variable load as needed, which sounds like exactly what you want.

Not actually true in the case of shunt regulators for permanent magnet alternators.  These typically use SCRs to shunt the phases, and even the MOSFET shunt regulators normally have the transistors either off or saturated.  This minimises power dissipation in the regulator, though increases I2R losses in the alternator.