Battery Boxes...What One Company Designed

Too_Many_Tools · 2005-09-16T16:23:51+00:00

Since I am starting the homepower/automated house journey, I have beencollecting surplus commercial equipment that might prove useful. One ofthose items was a surplus Best battery box for a large UPS. Somecomments on the construction and design follows.The box is designed for sealed 6v batteries (two banks or four) withthe second bank located above the first. The cabinet is metal withgalvenized trays for the batteries to sit in. The box was wired for 12vat 200 amp with commercial welding cable. There are two in line fuses,one per bank. The cabinet is on wheels. The cabinet has two ventslocated on the back of the cabinet, one lower and one higher. Thecabinet is NOT actively ventilated but relies on natural convection. Onthe front it has a single heavy duty switch to switch the directcurrent. The switch has a ceramic resistor on it (to quench arcs whenswitching?).Several things caught my attention. The use of metal throughout thebox...I would have expected fiberglass or plastic for corrosionresistance. Next was the absense of an active ventilation system.Third, the lack of an integrated charger for the battery box. I assumethe batteries are charged through the UPS.I plan on making some mods to this box for my home system.One is to make plastic tray inserts to keep acid at bay.Next is an active ventilation system.Third is to consider doing some type of a sliding tray on the bottomlevel to allow one to access the batteries easier during maintainance.Fourth is to incorporate a charging system.Fifth is to place meters on the front to monitor voltage and amperageand add the option for remote sensing.Sixth rewire it for a different voltage (it was 12v at 200a)...anysuggestions?I would be interested in any suggestions or comments as to what youhave added to or wish you had designed into your system.Thanks for any and all suggestions.TMT

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Marc F Hult 20 years ago

IOW, get back to the Q&A that might have transfer value to other folks. Thank you ;-)

Allow me to assert that, side for legacy requirements for some thermostats and HVAC controls, nearly all home automation/control/measurement electrical power needs are intrinsically DC. (Air conditioning, heating, large motors etc are beyond our scope here.)

The system I've described and shown in schematics consists in building blocks in increments of nominal 12vdc (~13.8 vdc. One can easily add additional voltages in series on _top_ of the 0-12-24vdc voltage, 80/60 amp configuration.

So I could create a 1.25 amp 48vdc supply with two 1.25amp 13.8vdc Powersonic wall-wart chargers and two 7AH sealed lead cells (the most cost-effective size) that I have on hand and move around for various projects. I have been using this particular combination from this supplier for isolated power supplies for environmental monitoring for at least 20 years.

This would provide a system with 0-12-24-36-48vdc at 80/60/1.25/1.25 amps

48vdc just doesn't happen to be needed in my case right now, which (based on the devices I have) _does_ need ~40 amps at nominal 24vdc to power the DC dimmers that I happen to use. Requirements of other folks will vary. Point is that the approach is modular, and one can move things around as needs change, which in a experimental/hobbyist environment, they inevitably do.

Recognize that if the battery bank weren't there, and aside from the specific listing issue, the 80-amp 12vdc "tap" is Class 1-compliant so one could partially "de-build" to reach a particular code goal/requirement should it come to that.

Using a 40 amp instead of 60amp charger/supply would make the 24vdc tap also Class 1 (same provisos).

No, in part because the DC-DC converters can be internal to the devices they power. Compare the hodge-potch of wall-warts, power strips, surge protectors, and local UPS's that conventionally are used to power a pc and associated accoutrements with these:

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(the 12vdc on the latter is pass-through, not regulated.

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Which, *inside* an (eg) low-power PC such as VIA EPIA is smaller, more energy efficient, has fewer connections to fail, and has longer battery backup among other things.

A standard/conventional hermaphroditic connector for DC connectors are the Anderson Powerpole series

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have been adopted by hams as informal quasi standard for Radio Amateur Civil Emergency Service (RACES) among others

Purchased inexpensively here:

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And recognize -- importantly! -- that the short back-up time on under-desk UP's don't actually solve *anything* if the PC is supposed to stay up permanently which is often the case in HA applications. So the conventional under-desk AC-based tangled jumble fails and the almost invisible, internal DC solution elegantly and dependably meets the needs.

Depending on the specific CPU requirements (part of this approach involves getting real with what we actually need in terms of computational horsepower) sufficient 5vdc and(or) 12vdc power may be available from the same DC-DC converter to supply a router or other gizmo. If not, add another DC-DC converter, perhaps within the same case, but certainly not on the wall or on an AC power strip.

I think that you are asking whether I use devices that can use unregulated nominal 12vdc or 24vdc. Yes. 12vdc devices abound. And this is a factor in my purchasing decisions. It also prompts me to take the covers off devices to see what their internal power supplies _really_ need.

.... Marc Marc_F_Hult

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Marc F Hult 20 years ago

Let me tackle the 'AC' part here.

(We need to stick to comparing pomes (as in apples to pears) so large diesel generators and other solutions beyond the modest ones previously implied are beyond the scope of the solutions to be discussed here.)

I've recently discussed the aesthetic problem of "wall acne" in a thread in comp.home.automation, so won't repeat that in this thread which is cross-posted. Let it suffice that there are advantages to low voltage distribution that are unrelated to the need for uninterrupted power. It is the need for UPS that I address here.

Starting from the design objective of making power available ad infinitum, not just for a few minutes to (eg) allow a computer to shut down. This (necessarily, methinks) results in a _central_ UPS system the power from which must be distributed as either DC or AC.

The DC supplies I've described provide about (60 x 14 + 80 x 14) =~ 2000 watts . Not coincidentally this is about what 15 amp (1800 watt) and 20 amp (2400 watt) AC circuits can provide.

Noting that in the US, the National Electrical Code prohibits supplying a (eg) a conventional wall outlet with less than a 15 amp source, it follows that an AC UPS with the same capacity as the DC system I described must be on a _single_ circuit There can be mo overcurrent protection between the panel and the outlet less than 15 amps.

So in a NEC-compliant 15-20 amp distributed 120vac UPS wiring system, *every* outlet goes dead if the trip point is exceeded.

Summary:

1) After putting all the most important devices that should never be allowed to go dead, a NEC-compliant AC system is vulnerable to someone plugging in a vacuum cleaner during Saturday house cleaning, or to a space heater plugged in during an emergency and shutting everything down. This is a recipe for certain failure in my opinion. With the DC distribution system I've described, over-voltatge protection can be used _ab_ libitum_ (although not necessarily as effectively as desired -- 'nuther topic ;-)

2) Elsewhere in this thread, Dan correctly notes that the DC system described requires running new/different wires. How does having power from a single ~

2000 watt UPS system distributed throughout the house obviate the need to have new/different wires? As best I know, it doesn't.

3) From the efficiency standpoint, DC distribution also has the advantage when efficiency is most needed, namely when running from batteries. In a DC distributed system, the power used by (eg) PC goes through exactly one DC-DC conversion (battery-> DC-DC converter inside PC). In a AC distributed system, there are at least twice as many conversions with attendant decrease in overall efficiency of battery utilization (battery--> DC_AC UPS -->

AC_DC_DC converter in computer).

Marc Marc_F_Hult

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