Dump load from battery rather than turbine?

[JeffBurright]

Hi all,
I have a small turbine installed on my sailboat using a 30V Ametek DC motor, and I want to make sure my charge control setup won't fry my batteries. Can the collected wisdom here please check out my setup and let me know your thoughts?

-- 30V Ametek DC motor, directly tied to 12V batteries through blocking diode and 20A fuse.
-- Charge controller connects to battery bank, then to a dump load consisting of 2 50W lights. When battery voltage reaches the trip point (~14V), the controller turns the lights on (using battery power, NOT generator power) until the battery voltage drops below the trip point. The generator always supplies power to the battery and never to the dump.

Does this control/dump scenario work assuming that the two lights sufficiently siphon the excess battery charge off the top of the bank? Do I need to worry at all about the fact that as much as 30 volts are pumping into my 12V batteries for sometimes hours at a time? Does input voltage even matter (aside from efficiency) so long as the battery capacity isn't overcharged?

In good winds I can clearly see the lights turn on and off periodically, so the setup appears to be working as I planned. However, one of the batteries in my bank turned out to be bad last month (no idea how long this was the case), and I want to make sure I didn't murder it by accidentally thinking I was clever.

Thanks,
Jeff

[Rover]

Your setup is fine, the batteries aren't seeing 30V , the voltage of the turbine is being held in place by the batteries.

I'm not a big fan of using light bulbs for dumpload (yes they work) , but not the most rugged dumpload, one or both burn out and you have no dumpload.

[ghurd]

What Rover said.

Light bulbs are not a good dump load. 
It goes past the poor reliability issues.
Most (all?) major controller manufactures specifically state light bulbs are NOT to be used as a dump load.
At least one manufacturer states using light bulbs as the dump load voids the controller's warranty.

And light bulbs are not really saving much money.
Suitable power resistors cost very little more than light bubs per amp dumped, and resistors last "forever".

One thing about the controller sounds a bit troubling to me-
"In good winds I can clearly see the lights turn on and off periodically"
That sounds a bit 'slow', and possibly relay based?
Most better controllers will have the bulbs glowing at changing and various intensities.

I suppose as long as it is working, and you are happy, then its all good,
but ditch the bulbs before the batteries or controller get ruined.

If you want visual indication it is dumping, add an LED bulb.
G-

[Ungrounded Lightning Rod]

I'm not a big fan of using light bulbs for dumpload (yes they work) , but not the most rugged dumpload, one or both burn out and you have no dumpload.

I second that.  You should use some good power resistors.  Not only do lamps burn out, but their cold resistance is drastically lower than their resistance at operating temperature.  This causes an inrush current when they are turned on, which puts a strain on the controller.  Its power switching transistor (or whatever) has to handle far more current than the average current rating of the lamps.

Also:  I don't see any hysteresis in that description of the controller.  There should be a slight spread between the turn-on and turn-off trip points, to keep it from oscillating when the voltage reaches dump level.

[TomW]

Jeff;

You are on the right track.

As Rover stated bulbs are less than ideal but do work (As long as they don't burn out). If you could use hot water maybe you could use a DC element in a water heater tank to preheat water? Put that waste to good use!

Batteries just die sometimes. Most are murdered, however by their owners. Unless they are sealed, keep them topped off with distilled water.  That is one way to murder them quickly. Letting them go low on electrolyte.

Good Luck with it.

Tom

[Rover]

Jeff, Parting thought, you don't also have a shore power charger on board?  ... (I have a boat as well) , and not knowing where you are moored, or slipped, frequency of visit , marine battery chargers are notorious for boiling down batteries.  I know, been many an occasion , specially after a winter, when I haven't been down to my slip in a while and I have minimal power due to boil off.

Add to this, my battery locker can easily see 110-120F in rhe summer.

[Bruce S]

Jeff;
 Could you give us a model of the charge controller?
There may be some "extras" you can do with it for the dump load.
As TomW said could be you could re-route that extra power for hot water.

Looks good so far.
Bruce S

[ghurd]

Also:  I don't see any hysteresis in that description of the controller.  There should be a slight spread between the turn-on and turn-off trip points, to keep it from oscillating when the voltage reaches dump level.

I took it as the opposite of oscillation.
To me, two 50W bulbs clearly turning on and off periodically sounds like an excessively whole bunch of hysteresis,
especially with an Ametek charging multiple batteries.
G-

[JeffBurright]

Thanks for the input. I've been afraid to reconnect my system since I found out about the dead battery. Your caution about the lightbulbs is fair - I used them mostly because they were the simplest to understand and wire together. One thing I've got going for me is that they're the little halogen bulbs with the double prong rather than classic lamp bulbs, which I tell myself are more rugged. . .  I'm also enough of a Nervous Nelly to test the dump regularly, so I'll ride it out a while longer and start researching alternatives.

Ghurd: the periodic on/off of the lights is a function of the controller, which checks the battery voltage every 5 seconds and trips an automotive relay when necessary. When the batteries are topped off and the turbine's spinning, this can cause oscillation in the dump activation as the battery voltage bobs along the trip point.  C'est la vie, it was a $40 kit from ebay.

ULR: I'd have to check my documentation again to see if it even has built in hysteresis, but the oscillation shouldn't really be an issue should it?

Cheers, and thanks again!

[Rover]

If you hear a click when it goes into dump while onboard, its relay based. And if its relay based , the frequent on/off wil eventaully end the life of the relay.

Although Ghurd's dumpload is actually cheaper, it is not relay based ( and highly unusual fo it to be cheaper) , but if you spent only 40$ on ebay , I'd be willing to bet it is a relay based dumpload controller.

Your 40$ did not buy a name brand charge controller..

[Ungrounded Lightning Rod]

Also:  I don't see any hysteresis in that description of the controller.  There should be a slight spread between the turn-on and turn-off trip points, to keep it from oscillating when the voltage reaches dump level.

I took it as the opposite of oscillation.
To me, two 50W bulbs clearly turning on and off periodically sounds like an excessively whole bunch of hysteresis,
especially with an Ametek charging multiple batteries.
G-

Yeah.  I read too fast and missed the thing about the slow on/off cycle.