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Old 26-07-2012, 02:46   #1
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Load Dump on a Tristar MPPT 60 A?

Olá
Im just wondering if anyone has a load dump set up with this controller and how its done. I currently have 540w of 24v panels going into it and 12v coming out to my battery bank. Id like to divert the excess charge on sunny days to a twin element water heater like this
Water Heating Element for 12V or 24V DC
with one element as the load dump and the other wired via a switch to the battery bank.
Can it be done with the tristar controller or do I need additional equipment?
Thanks
Monte.
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Old 26-07-2012, 03:16   #2
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Re: Load Dump on a Tristar MPPT 60 A?

The simplest way is to use there Tristar Relay Driver Module and set the battery threshold , hence the relay switches at a high voltage and you can use that to switch the feed to the immersion.

However, this concept of load dumping is rather mis-understood. A solar panel doesn't generate excess current, it merely supplies what the load needs.

SO the easiest way would be to connect the immersion to the battery and then use a conventional standard voltage sensed relay (VSR, ACR etc) , as used in charging circuits, to protect the battery and switch on the immersion whenever the battery voltage was above normal conditions, ( i.e. when ANY charging circuits was active). If you want to restrict it to the solar panel, then a feed the sense voltage from the solar controller to the VSR via a diode splitter to isolate it from the other charging sources.


I think this solar "load dumping" concept comes from wind generator regulator technology which used crude high power resistors to dump load, ( this is because its a a permanent magnet Dc generator, this is not the case for solar)


Dave
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Old 26-07-2012, 03:52   #3
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Re: Load Dump on a Tristar MPPT 60 A?

Thanks Dave, that sounds pretty technical. Can you come to Portugal and do it for me??!
I dint want to restrict it to solar. I would just prefer heat the water when there is excess charge. I have solar and wind so the second option sounds suitable.
So would I use something like this
Voltage Sensitive Relay 125a Dual Sensing | eBay
And connect the battery bank directly to the relay and then to the element in parallel - 817W 60A -
or is there a more suitable VSR?
So basically it would connect to the battery +ve and the -ve (after the monitor shunt) and the element. 4 connections. And it will switch on whenever the battery voltage is over...13.7 V ?
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Old 26-07-2012, 06:44   #4
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Re: Load Dump on a Tristar MPPT 60 A?

Thats the idea, There are several on the market ( you don't need dual sensing, in fact you don't want dual sensing) note that the battery has to remain above the 12.7 to 12.35 ( depending on make) to keep the relay closed, so if you have a load on the battery, the relay will not stay closed , but then thats what you want.

You only need a simple two terminal relay, positive from the battery to the relay , positive from the relay to the immersion, when the battery voltage is above the switch point the relay will close, connecting in the immersion , when it falls it will disconnect the immersion, This will work with all charge sources, obviously wire an on.off and a bypass switch to manually control the immersion,

Theres no need to switch the negative,

You may find if there is load on the battery that the relay constantly switches over and back, so its not a fully automatic system. more then likely the solar/wind will not generate enough charge to solely power the immersion, so the battery will continue, until the voltages falls and the relay trips out.


Blue sea also make some, with a lower dropout voltage too , it would seem.

Google voltage sensed relays, there are many programmable typos available through industrial distributors.

heres another http://www.the12voltshop.co.uk/Shop/...lay-60amp.html a lot cheaper, though 12.8 is quite a high dropout voltage

True charge diversion/dumping really needs a custom solar/wind regulator


Portugal , love to, but currently sailing in france!

Dave
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Old 26-07-2012, 09:45   #5
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Re: Load Dump on a Tristar MPPT 60 A?

Just be aware of stam explosions or venting solutions when the tank reaches the boiling point !!
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