A controller of a kind.

[biff]

 I have been using heavy duty cables to restrict the voltage into a forklift pack,
This is a heavy duty 72volt  forklift charging cable approx 14ft long. if I connect it to the end of a 66ft long 64 sq cable running from my 330watt x 72v array on the lawn to the 48 volt x 400ah forklift pack, i can restrict the incoming voltage to the pack down to 53 volts, Open voltage in the nearby andersons can be 85+ but the moment it is connected to the pack, it drops to 53v and refuses to rise above 53v absolute max..even in prolonged sunlight.
  So i remove the forklift cables
by undoing these pair of Biff special bolt on connectors, insulated with plastic from water bottles,and taped together with ordinary insulating tape,,crude but rather effective. Then I gently connect up a set of 64sq cables and clamp them on to the forklift pack,

and as you can see the voltage jumps up into the late 50s. it will peak @ 59 volts no matter how strong and long the sun shines.The only thing you have to watch is the danger of the acid in the pack sizzling and fizzling away. So it is not a good idea to leave it such, unattended while not under load.. I have had this pack for a good few years now. I built the shed with it, the same 330watt panels can dish out 450 watt. The system drove my little cement mixer, drove the grinders and drills,charged cordless,s without ever being discharged. The whole lot was looked after by a 1kw chinese controller/inverter which can still perform perfectly when needed.
  It is interesting that a large lump of copper cable at the end of the 66ft of 64sq can act like a controller. It does have an anderson connector in the middle of it,,if that would make a difference but i think it is just the amount of copper that the volts and amps have to try and push through to finally get to the pack that creates the resistance and lowers the voltage.
  So one could work out the weight and the length of the copper required to keep a set voltage from a set array, to a set pack under control without getting too fancy.
                                                              Biff

[billi]

wow Biff .... we have give this controller a name ,I guess .... is the 72 Volt array  a part of your 120 volt  setup? 
how much Amps do arrive then at battery ...

[desperate]

Or you could tie some knots in the cables

Desp

[biff]

Nope billi,
       It is a completely different system,.It would be a usefull way of preventing overcharging if one blew a controller and had to wait for a replacement..
    Hi Desp, there is a thingwayjigger called a choke on the end of a transformer already..It is a big knott of copper wire..
                                                        Biff

[johnrae]

I'll take the bait   

A length of cable is not a controller and really cannot be recommended !

It is simply a resistor which drops voltage depending upon the current passing through it.

As you battery voltage rises to its designed float voltage, the current will decrease and the output from the cables will increase which means the battery voltage is pushed beyond their design parameters.  That's why the keep 'sizzling and fizzling away".  It's not the acid which disappears, it's the water content of the acid which means its ph value falls (acid gets 'stronger')

When all is said and done, you are shortening the life of your batteries, even if you've been running them like this for some time.

[biff]

Thanks Johnrae,
                Now when I say they sizzle and fizzle , I exaggerate , I really do, The most they do is send up a tiny bubble every 20 t0 30 seconds and I am of course aware that the liquid contents will evaporate of they sizzle and frizzle, so I say this as a warning to anyone who tries it ,so as to be sure to keep their eye on the ball.
  Now I would assume that if the current/voltage cannot get through the large copper cable quick enough, then it will back up and dissipate out through the face of the pv panels in the form of heat.
  The dump load voltage on our off grid house system is 138/9vdc,, every few months I give it a midday boost ,by disconnecting one of our 2 x ,2kw  x 138volt immersions , this allows the voltage to climb up the scale as far as 146v max for a half hour or so,,now that would encourage a bit of genuine fizzling and sizzling but nothing to be worried about, once the second dump load is reconnected, it is back to business as usual, The forklift cells are then rechecked  and everything is hunky dory.
 My cable idea is of course not a genuine controller but could pull some one out of a jam if they had to wait for a few weeks for a replacement controller. I am guessing that the voltage can be controlled by the weight and length of the copper cable which could be calculated by a little trial and error . 14ft of chunky forklift charging cable can resist a lot of power,the same cable stays as cold as the floor it lies on.It is interesting in so much as a simple change like that can alter the whole dynamics and accidentally solve a problem that I did not have. 
                                                                          Biff