controller settings for diversion load and generators... [RE-wrenches]

[David Katz]

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Hugh,
I have been using an Enermax charge control for may years to divert 
excess power to water heating.  It operates like the C40 or Tristar in 
diversion mode and I have run into the same problems.
You can put a normally closed 60 amp contactor in series with the 
diversion load, with the coil powered by AC from the generator so that 
the diversion load is inoperative when the generator is running, 
assuming that the generator is only running when you are bulk charging.  
It usually doesn't make sense to float charge from a generator. Be very 
careful to follow the manufacturers instructions about voltage with gel 
or AGM batteries and definitely use temperature compensation.
For loads sensitive to high voltage, put two silicon diodes with an 
appropriate current rating (on a heat sink) in series with the load and 
put a normally closed contactor across the diodes that is powered by the 
a voltage controlled switch from Solar Converters or the auxiliary relay 
in an Outback or Xantrex SW inverter.  The new Relay Driver from 
Morningstar is also an excellent choice to activate control relays.  
When the relay opens, the voltage to the load will drop by 1.4 volts.  
If you set it to open at 29.5, the load will see about 28 volts and go 
up to 29.5 when the battery reaches 31 volts. Set the relay to close 
again at around 28 volts.
Cheers,
David

David Katz
President, AEE Solar
formerly Alternative Energy Engineering
1155 Redway Drive - Box 339
Redway, CA 95560 USA
Phone (707) 825-1200
Fax (707) 825-1202
email: david at aeesolar.com
web: www.aeesolar.com


Hugh wrote:

> I'd like comments on an old but little discussed problem.  It relates 
> to wind or hydro systems (or even PV) where a diversion load is used 
> for charge control for example with a c-40 or tristar.  There is also 
> an engine driven generator on the system and it feeds into the 
> inverter (SW, FX, studer, whatever) and this charges the battery.
>
> At a certain point the charge controller will go to float the battery 
> and if the inverter is still trying to bulk it then you will have the 
> controller maxed out on heating something at the expense of engine 
> fuel.  YOu can tinker around with settings on the inverter and the 
> controller but it is hard to get a satisfactory arrangement that 
> charges the battery properly.
>
> I have used a blocking diode to solve this by making sure that the 
> diversion current all comes from the renewables but this is not ideal 
> - leads to vibration in the turbine and stuff like that.
>
> another question.  What bulk setting do you guys use for gel batteries 
> (eg Fullriver HL series) and how do you ensure that they do not gas 
> and lose electrolyte.  My supplier recently told me to use 29.6 volts 
> for a bulk charge.  I am pretty sure this could lead to problems since 
> the controller will not really 'know' when exactly to go to float 
> voltage and I can foresee some loss of electrolyte, no?
>
> Then there is temp compensation.  This can push the charging voltage 
> up to 31 and trip the inverter.  I have a client runnning datalogging 
> equipment and the supply must never go above 30 volts but in cold 
> weather the battery 'needs' to get up to 31.  what to do?
>
> Lots of little puzzles.  Any comments welcome.  It shows how immature 
> the small wind industry is that the controllers you buy do not have 
> inherent solutions to these problems (except perhaps the outback 
> products that talk with each other - but how many people can figure 
> out how to program all of that?)

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