12V and Power supply mix?

[dashunde]

I'm building a 110v powered "charging station" using a 30a 12v P/S and two or three Cellpro's - mostly for at home use. But I'd also like to power the chargers in the field by tapping into the three 12v 7A SLA batteries within the box on the left.

Do I have to use a switch to isolate the P/S outputs from the 12v input of the SLA's?
It seems logical to isolate with a DP/DT switch, but I'd like to get away without it if I could (clutter/complexity).

[Tomapowa]

First!....Oh please ....Oh please tell me you do not store (never mind charge) your LiPos in your field box like you have shown... :eek: :eek: :eek:

To your question... not sure on your exact hookup/wiring but it sounds like you will have the output of the powersupply (right) hooked up to a few chargers (100VAV -> Powersupply -> 12v output -> Chargers), and you want to be able to supply these chargers (all requiring 12v input) with voltage from your other field box (3 SLA batteries assumed in paralled). Sounds like your question is whether you need to disconnect the chargers from the powersupply before connecting them to the SLA batteries.... quick answer is... not sure! It all depends on your power supply and whether it includes blocking diodes and/or circuitry that allows this. Most likely (assuming oyur powersupply is a basic computer/electronic power supply) you will need to remove the connection between the chargers and powersupply first before connecting the chargers to your SLA batteries. Better safe than sorry I say. Most battery chargers (units designed specifically for charging batteries, not a simply power supply) already have a blocking diode which allows you to remove power from the charger and not have the battery voltage backfeed into the charger/supply. So, unless you know for sure your power supply has blocking diodes, I would use a switch of some sort to switch chargers from AC/Powersupply to SLA batteries. Your last option would be to incorporate a Schottky power diode (http://www.fairchildsemi.com/ds/MB%2FMBR1035.pdf) between the supply output and charger inputs (of course, it's rating must be >= the max Voltage & current draw from batteries).

Here's an example:
http://www.emrg.ca/pwr_supply_gelcell_charger.htm
It shows a circuit for power supply that is capable of providing power to a circuit (radio) while charging the backup battery. In your case, as long as you remember to not plug in your power supply when using the batteries, you can eliminate R1 and D2 (in your case, the Radio chown in the diagram would be your chargers, D1 is the Schottky diode)
http://www.emrg.ca/pwr_supply_gelcell_charger_files/Image7.gif

[dashunde]

Thank you much... just what I was looking for.
I suppose the complexity of a simple switch is the lesser of the two options.
The P/S is a nice unit made in Italy (Dont remember the name at the moment), and at this point considering its made for a server, I'll err on the side of caution and assume it has no backfeed protection (why would it?).

Yea... the lipos are stored in that box, but never charged within.
During charging they are connected to the cp adapter (seen hanging near the front) and dropped into a tall, heavyweight, ceramic coffee mug.
Currently, most all of those packs are brand new (except the 1350's) and are at storage voltage.
I have a good deal of faith (as much as reasonably possible) in the CP's charging safety (still always use the mugs), but yes... I do have concerns about storing them all together like that.
What other reasonable option is there? Scatter them all over the house? Not gonna happen.
As foolhardy as it sounds, I trust the Rhino's - this is my second full round of Zippy/Rhino packs and I've had zero trouble with any of them - not even so much as a errant cell voltage or puff. I cant say the same for the two TP's I've had thus far.
Honestly... I have greater concern about the 30 year old gas and electric lines in our college town rental house - a real creampuff of a place lemme tell you. Thank God its temporary :p

[Tomapowa]

Glad the info helped.
And if you plan to use a switch, you probably only need a SPDT type.. as you only will need to switch the "+" side of battey/supply... common ground should be OK.... just as long as you never plan to be using the batteries and power supply at the same time (could get into a serious ground loop issue).

Sry for my LiPo concerns...I just get scared as heck when I see LiPo hanging around. I'm certainly glad to hear you charge them in a container of some sort. I store/charge/transport my LiPos in a cheap sand/cement-lined fire-proof safe such as: http://www.walmart.com/catalog/product.do?product_id=5127160 Another item I now store in my flight box is a small ABC extinguisher... never know when you'd need it (for R/C or not).

[ghoti]

There is a lot of stored energy closely packed in your wood box. If any one pack should ignite they all will by runaway chain reaction. i would no more store it indoors than I would a gallon jug of gasoline. Bill

[dmccormick001]

Several of the members in my club have started storing their Li-Pos in individual zip-lock type plastic bags to keep them from shorting each other out. It kinda gives you an extra layer of protection from a couple of connectors getting together and causing a problem.