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Author Topic: Question - parallel batteries w/Astron PS  (Read 1196 times)
NZ0T
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Posts: 74




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« on: February 02, 2012, 10:38:50 AM »

I have 4 40AH SLA batteries wired in parallel that I have connected to an Astron RS-35M with the  float backup mod done.  I have this wired with the Astron feeding the batteries and then the load (all the 12V stuff in the shack) connected to the batteries.  Physically I have the wires from the power supply and the lead wores connected together at the terminals of the last battery in the parallel setup.  Is this correct or should I have one lead going to the positive terminal of the first battery and the other to the negative terminal of the last battery, or vice versa?  Seems to me that would equalize both the charge and the load distrubution between all 4 batteries whereas the way I have it now means that last battery is loaded and charged more than the other 3.
Or does matter at all?

73 Bill NZ0T
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N4HRA
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Posts: 280




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« Reply #1 on: February 02, 2012, 11:03:48 AM »

Put a fuse in series with each battery pos. term and the power lead.
those batties do have high short circuit current

just my 2 cents

Lew
N4HRA
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KD8DEY
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Posts: 352




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« Reply #2 on: February 02, 2012, 11:12:04 AM »

Remember if you decide to swap to deep cycle marine batteries for more
capacity to turn the voltage down to 13.5 Smiley
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NZ0T
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Posts: 74




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« Reply #3 on: February 02, 2012, 11:12:46 AM »

They are fused.
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WX7G
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Posts: 6039




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« Reply #4 on: February 02, 2012, 12:19:35 PM »

Yes to balance the charge/discharge current connect (as you say) the positive load wire and RS-35M wire to one battery and the negative load wire and RS-35M wire to the other battery. One fuse from the RS-35M will do. Placing a fuse for each battery will upset this balancing topology. A single fuse from the RS-35M will suffice.
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W6EM
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Posts: 794




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« Reply #5 on: February 03, 2012, 06:33:49 PM »

Don't understand the "only one fuse" comment, as the addition of fuses in each positive leg will introduce a very small incremental resistance of almost the same value into each terminal lead.  And maybe save you a catastrophic situation in the event of an internal short in one of them.

Yes, do fuse the supply.  If your supply lead is a small wire, you don't want it to be your fuse if a power supply crowbar should operate.......    Fused copper at 1083C may not happen, but melted PVC isn't cool either.  Also, if your Astron is de-energized, it will be back fed from the batteries unless you have either an isolating low Vfd series Schottky diode or a drop out relay to isolate it.

To properly balance a heavy load among paralleled batteries, best to equalize the terminal lead lengths to a common bus or tie point.  That way, with all things being equal in battery characteristics, if they truly are, then you will have equal voltage drops and resultant current contribution from each paralleled battery.  Float charging lead connection makes no difference since only a few mA and negligible voltage drop in the leads when all batteries are fully charged and no interchange current is flowing.

Also, make sure you have good ventillation as vented lead acid cells can off gas hydrogen, and create an explosive situation.  I seem to remember a minimum ventillation of at least 4 complete air changes per hour of battery area atmosphere.

Hope this helps.

73,

Lee
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