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How to clamp max voltage?
By Shadow, Section Controls Posted on Sat Oct 10, 2009 at 07:25:06 AM MST
Max Voltage clamp needed

I'm hooking up a vintage Jacobs wind generator rated 110 volt DC, 140 volt max.
I will be using an Outback mppt controller to charge the 48 volt battery bank.
The charge controller has a ABSOLUTE max input voltage of 150 volts cold. Thats way to close to the max voltage of the generator. What can I use , or how can I go about clamping the voltage from the wind gen to NEVER go higher than 140 volts? Thanks.

How to clamp max voltage? | 9 comments (9 topical)

Re: How to clamp max voltage? (3.00 / 0) (#1)
by Flux on Sat Oct 10, 2009 at 08:25:30 AM MST

Thought I posted to this so forgive me if you get two versions.

You should be able to alter the blade pitch governor springs to reduce the top speed. With a bit of luck you will be able to limit the open circuit voltage to a safe value.

If that fails it is a shunt machine and you can devise a field regulator to keep the volts down, much easier than having to control the full machine output as for a furling pma.

Re: How to clamp max voltage? (3.00 / 0) (#2)
by Flux on Sat Oct 10, 2009 at 08:36:53 AM MST

On further thoughts I doubt that speed alone will let you keep the volts down as the thing was designed for a voltage higher than you can tolerate, the field will not be in saturation at 140v and you may be on the unstable part of the field curve. It's not like a pma where output volts are directly related to speed. That only applies to a shunt machine once you saturate the field.

A field regulator should be a very practical idea but as always it involves electronics. a crude way would be to parallel the field coils and include a series ballast resistor, that way you could limit the armature volts on speed but with a much higher field loss which will mess up your low wind performance. The best solutions will be electronic.
Flux

Re: How to clamp max voltage? (3.00 / 0) (#3)
by cardamon on Sat Oct 10, 2009 at 06:50:16 PM MST

How about using a relay to switch in some more loading if the voltage gets, say, above 120v? If you are like me and not real hot with electronics then you should be able to figure something out with stock components like driving the coil of a relay right off the turbine voltage and have that connect some more loading to pull the voltage down. of course you would have to find a relay that does this at the right time or play with the control circuit a bit. Digi-key has a good selection. There are some voltage controlled switches out there too, I know solar converters makes one and I think I saw one in the backwoods solar catalog, but I doubt they go that high for the control voltage. Maybe a proportional dc-dc converter or voltage divider circuit would work in conjunction.

Re: How to clamp max voltage? (3.00 / 0) (#4)
by Shadow on Sat Oct 10, 2009 at 09:24:32 PM MST

Thanks for the replys, I'm sure I saw something along the line of a voltage clamping switch but not sure where.

I have a couple large Rheostats, could they be used to set the voltage or are they more for controlling current? Could one be put on the field current? As I understand it if the field is limited the total output should be limited?

Re: How to clamp max voltage? (3.00 / 0) (#5)
by Flux on Sun Oct 11, 2009 at 01:42:09 AM MST

A shunt machine will behave as a pma if you keep the field constant, the armature voltage will be directly related to speed so if you limit the speed as in this case it will settle to constant open circuit voltage, but that figure is probably going to be well above your 140v unless you severely limit speed or clamp the field to way under its normal value.

I don't know how easy it is for you to get at the field, if it is brought down you have more chances than if the field is directly connected to the armature on the machine.

Series field resistors aren't going to work, they make a shunt machine less stable and you will have trouble getting it to self excite and they will make the open circuit voltage more speed sensitive.

A small amount of series resistance with a voltage clamp across the field winding to hold it at perhaps 100v may get you into the region where blade speed will do what you want.

The ideal field regulator will give you full field under working conditions but would weaken the field as soon as your armature voltage exceeded your limit. This would be a device like a big car alternator regulator.Not at all difficult to do but it is an electronic method and is not for everyone. I see no hope of doing it with relays, it will just chatter on and off ( this is virtually the old sparking contact dynamo car regulator and even with a diode across the field I am not convinced it would last long at 120v).

If you got your mppt controller to load properly you may find that the on load volts don't go over your limit, in which case you would only need to protect the converter if you lost the load. In this case a device that removed the field would protect you and the blade pitch regulator would protect the machine.

Whether you can get the converter programmed to load it correctly and fast enough to keep input volts within limits I don't know, I have no direct experience with those mppt controllers.

You could use a clipper directly on the armature output just as the furling pma people have to do with a mppt converter but that is a serious sized dump controller and a bit of elaborate electronics. if you can do it on the field you are only looking at a low power regulator.

Flux

[ Parent ]

Re: How to clamp max voltage? (3.00 / 0) (#6)
by cardamon on Sun Oct 11, 2009 at 06:25:05 AM MST

By the way, what was the original intended use for that odd output? My father had a jocobs back in the 70's but I do not recall what voltage the system was.

Re: How to clamp max voltage? (3.00 / 0) (#7)
by Shadow on Sun Oct 11, 2009 at 08:34:29 AM MST

Thanks Flux,
This does have a field wire that runs down the tower. So maybe able to work with that.

Cardamon, These machines were mostly used for small villages, ranches and such. You would have needed 55 2volt cells so fairly pricy for those days.

Jacobs only made a 32 volt or 110 volt at the time.But they are built to last a life time. This one weighs 440 lbs.

Re: How to clamp max voltage? (3.00 / 0) (#8)
by DanG on Sun Oct 11, 2009 at 01:31:40 PM MST

Why not use a step-down transformer / transformers?

It could be one or three DIY Toroidals and drop voltage 30% etc. (Always wanted to make a huge one myself)

Or, whatever is handy on craigslist or eBay in a 1:2 ratio?

Re: How to clamp max voltage? (3.00 / 0) (#9)
by Flux on Mon Oct 12, 2009 at 12:25:54 AM MST

Not in this case. The old Jakes use a dc dynamo, there is no ac to transform or rectifiers. This is where the mppt converter is being used as a dc transformer more so than for it's mppt properties.

Flux

[ Parent ]

How to clamp max voltage? | 9 comments (9 topical)

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