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> Battery Box Construction
Jimthecopierwrench
Posted: November 20, 2011 09:58 am
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Laying out the morning's work for a battery box for you know what and trying to work out a few issues.

I want to switch the main cable remotely, aka relay, but can't afford the coil current required for most realys of this calibre. In fact ideally, I'd like the relay to have no parasitic drain either open or closed. Any ideas?

Best I can come up with is trying to fashion a lever system to open or close the knife switch contacts from an old school (mains) disconnect box. Although the contacts (~3/16" thick, with the throw 1/2" wide) are only rated for 100A my guts tell me they'll hold up for years with with the intermittent nature of current above this level. As well, the switch will never be operated with the batteries loaded anyway - the function is to simply disconnect the battery box when it's not required but still allow it to connect to the primary batteries (for cranking) should they ever go flat.

Problem is the door lock actuator I'm thinking about doing the switching duty probably isn't strong enough to dis/engage the switch, and levered wouldn't have sufficient throw (stroke).

Other thing is bus material. Noticed some trucks have gone to steel straps. I'm using a marine type clamp terminal with a 5/16? 3/8? Can't recall - thread for connecting cables. Not sure if the clamps are lead or not - they don't seem to be as soft as automotive clamps. An alloy?

Trying to figure out the best mix of all the metals together for the most trouble free operation. Should I buy some copper bar stock, or will aluminum or steel be good enough for the job?

And last... That fuzzy terminal corrosion. I've got 3 identical batteries that were charged in parallel a few months ago, sitting together (unconnected and open) on a piece of plywood. One of the three has discharged and has grown a massive fuzzy beard of corrosion on it's positive terminal. Why just that one?


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MacFromOK
Posted: November 20, 2011 10:02 am
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Bear in mind that switch current rating is for hot switching. If you don't switch it while cranking the engine, 100A is probably overkill (it may run 500A or more without a make/break episode).

And I'd stay with copper bus material. There's a reason it's the ol' standby.

QUOTE (Jimthecopierwrench @ November 20, 2011 02:58 am)
And last... That fuzzy terminal corrosion. I've got 3 identical batteries that were charged in parallel a few months ago, sitting together (unconnected and open) on a piece of plywood. One of the three has discharged and has grown a massive fuzzy beard of corrosion on it's positive terminal. Why just that one?

IME, that's practically a moot issue. For unknown reasons (lol, to me anyway), some batteries leech more acid onto the surface than others, which results in more corrosion on terminals. Perhaps the seal between case and post is a bit wonky, dunno.

And there may very well be a more sane (or less insane) explanation... beer.gif


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CWB
Posted: November 20, 2011 01:19 pm
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yep ...
i'd go with the electrolyte "wicking" up around the post and a current path to the other terminal (contaminated surface that is hygroscopic ?) .

as for a disconnect ... a motor driven "snap" type connect/disconnect/changeover switch was used in many of the flip-flopped or standby generator sets .
you might check with some of the industrial places that handle generators (the fair sized ones) and switching gear ...
they might have something in the bone pile that could be had for little money .

there are also dual coil contactors that use a high current winding to rapidly and solidly make the connection and then switch over to a low current winding to hold the armature in place (think dual windings on a pinball machine flipper actuator solenoid) ...
hey , perhaps that is an idea too .

elsewise ... how about using some fets . the current required to bias them "off" would be pretty low .
a couple of the other guys would be able to provide suggestions along these lines ,



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tekwiz
Posted: November 21, 2011 12:10 am
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My beast has an emergency starting system that connects both batteries when necessary. It is extremely simple...a starter solenoid & a momentary contact PB on the dash. A diode isolator is used to charge both batteries.

To minimize corrosion issues, use as few different metals as possible, especially for the current carrying components. I wouldn't use steel.

That corrosion problem is symptomatic of a faulty terminal seal. It shouldn't be an immediate problem, but will increase maintenance. Make sure to keep that area well covered in grease if you use that battery.


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johansen
Posted: November 21, 2011 12:39 am
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Use a 200 amp circuit breaker (2 poles, gives you ~800 amps for 10-30 seconds before it trips) if you have one. though it seems they cost 200$ these days, as if the contacts were made out of a platinum alloy or something.
The door lock actuator should have sufficient strength to flip a breaker.


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Jimthecopierwrench
Posted: November 21, 2011 01:24 am
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QUOTE
It is extremely simple...a starter solenoid & a momentary contact PB on the dash.
And there's the problem with planning the day's work before food or coffee. Duh. Of course that'll work as the heavy main will only need to be energized IF I need that box to assist starting. (The other 12AWG lines coming from the box and doing what they have to were never a switching 'issue' so for some reason I was focusing on how to disconnect the main cable - 14 hours later and thinking back I have no idea where the hell my brain was at. Ah well laugh.gif



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GPG
Posted: November 21, 2011 04:30 am
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Some starter solenoids won't work without a load. These have two windings, one connected to the output terminal, the other to earth. The one to the load pulls the relay in through the starter load and then is effectively taken out of circuit by the voltage on the output terminal. The other is the hold coil.
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Jimthecopierwrench
Posted: November 21, 2011 06:34 am
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Not sure I've seen one like that, but the old Ford 'left side fender' types well into the 90's were just a simple solenoid and are still common, compact, and cheap.

For the most part finished the box http://i815.photobucket.com/albums/zz79/Ji...us/DSCN3338.jpg

Getting late now, so it's going to have to be a night.


Only thing left to do is cut a window for a pair of cheap LED voltmeters I ordered from DX - they'll be good enoiugh for the purpose - and will be energized by a low side momentary switch, drill and grommet the main cable (and relay) through the side of the footwell. Note that the starter motor is less than a 1-1/2' from the front battery positive terminal - and the OEM cable almost 9 feet long, so you can see why the option to start with these batteries is attractive.

The vent will empty into the door pocket and out through a 2" hole I've cut on the inside of it below the floor - no problem there.

Will need to adhere some sound deadener to the inside of the box though.


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Colt45
Posted: November 21, 2011 09:09 am
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Looks good. Yeah an old ford solenoid should be fine, I would think.

Keep in mind, I don't think they're rated for continuous duty, so... You might want a diode from the alt, for charging, and short it with the solenoid when starting, if this battery is for 'other duty' during normal operation. If you need it on the same circuit I guess you could have a wussier relay that is continuous duty when the thing is running.


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tekwiz
Posted: November 21, 2011 09:46 pm
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QUOTE (Colt45 @ November 21, 2011 12:09 am)
Looks good. Yeah an old ford solenoid should be fine, I would think.

Keep in mind, I don't think they're rated for continuous duty, so... You might want  a diode from the alt, for charging, and short it with the solenoid when starting, if this battery is for 'other duty' during normal operation. If you need it on the same circuit I guess you could have a wussier relay that is continuous duty when the thing is running.

That's what diode battery isolators are for. These can be used as high current terminals simply by making the connection wires to the batteries big enough.
That's how I set thing up in my beast, because it means only one cable to the coach battery. Everything else hooks to the isolator, which is mounted under the hood with the vehicle battery. The coach battery is under the floor in front of the passenger seat.

I put twin backlit LCD voltmeters in a pod on top of the dash. They draw so little current that I generally leave them on all the time, with a switch to turn the backlights off for long term storage. The pod itself is optional OEM & used to hold idiot lights & a tranny temp guage. These functions will go to digital dash guages. wink.gif


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For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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GPG
Posted: November 22, 2011 02:38 am
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QUOTE
Not sure I've seen one like that,
Seen a few but recalling, they were mostly in heavy machinery
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