JW power supply

[Philip Perkins]

The simplest way to describe the cart power supplies I have been building for the last 10 years or so is to let you know the main components: sealed lead acid batteries and regulated DC power supply --- it's that simple. No charge circuit, no standby UPS stuff, no inverters, etc. I use either linear power supplies (with transformers and available new or through surplus) or switching power supplies (more on the type later) that when plugged into AC (usually 90 volts to 240 volts) put out 13.8 volts DC at around 10 amps. This is connected to the battery and then the equipment, the load, is also connected to the battery. When plugged into AC, the DC from the power supply floats across the battery keeping a fully charged battery, fully charged. When the equipment is powered up and drawing considerably less than 10 amps, the battery stays charged and everything is happy. If there is no AC or the AC gets pulled accidentally (does that every happen?) the equipment is still getting DC but now off of only the battery. There is no noise, no charging circuit to introduce any trouble, the equipment is quite happy to be powered off the battery. When the AC returns, whatever has been drawn off the battery is replenished. It is an elegantly simple system that has been 100% reliable for the last 10 years or so.

There are a few caveats: if you use switching power supplies you must purchase supplies that have a low noise and low AC ripple spec (but most of the medical grade supplies work very well in this respect) and they must have an amperage rating that is greater than the maximum current draw you have will all equipment powered up. Secondly, you must choose a battery type that is suitable for constant current across and this type is generally the sort that is used in backup lighting systems, alarm systems, any place where the battery is happy in a stand by mode. Then you choose how many amp hour capacity you want based on how long you want your equipment to run off the battery alone. In my case I have 35 amp hour battery which will run everything on my cart for 6 hours. Lastly, you must start out with fully charged battery so that means having a conventional battery charger available. The float system relies on having a fully charged battery so if the cart has been sitting around for a long time and the battery is discharged, it should be fully charged before using this system in production.

All of this stuff is housed in some appropriate case or chassis box with everything fuse protected and multiple 4-pin XLR outputs as needed for distribution. On my cart there is one connection to this box and then my cart is internally wired with several DC connection points in the proper places for the equipment in use. I also made the wiring from all these connection points "home runs" meaning there is a continuous wire from each connection point back to the power supply. Rather than looping through each connection point this seems to cut down on interaction amongst the equipment.

Regards,  Jeff Wexler

I thought I'd get this off the "Berlin Cart" thread.

Jeff--when you say that the power supply feeds the battery which then feeds the equipment, how are you connecting this?  PSU to battery terminals, then batt terminals to DC distro on the cart?  I want to try to hook my gear this way--I think I have all the "big" pieces already.

thanks

Philip Perkins

[Jeff Wexler]

Jeff--when you say that the power supply feeds the battery which then feeds the equipment, how are you connecting this?  PSU to battery terminals, then batt terminals to DC distro on the cart?

Philip Perkins

Yes, exactly. The regulated DC power supply (I can also post some links to the ones I have used, both linear - heavy! and switching) is connected to the battery terminals and the also the distribution to the cart to the same terminals. So, in essence when the regulated DC supply is "on" the equipment (the load) AND the battery are being fed 13.8 vdc. This works out to not be exactly like powering the equipment directly off the power supply because the battery is connected also and serves as a big buffer lessening any AC ripple that could come through. I did do one supply where I put a diode between the battery and the power supply so that when not in use DC would not flow back into the power supply. I don't do that anymore but I do have a breaker/fuse/switch so that when cart sits for weeks and weeks not working I can disconnect the power supply from the battery.

Regards,  Jeff Wexler

[Noah Timan]

I've used this same sort of system for years now with very good results.  One way around the problem Jeff notes here is simply to put connectors between the various pieces, rather than wiring the power supply directly to the battery terminals.  This allows for a very simple connect/disconnect scenario.  Most of the power supplies (linear) that I use have banana plugs on them and I just made up a few banana plug to XLR4 cables, and put a standard panel-mount mating XLR4 on the battery case and wired that to the terminals.  It allows for the system to be very modular and to have the ability use different batteries, power supplies, etc.  This kind of system is maybe less-elegant looking than the expensive PSC systems, but it improves on them in several notable ways. 

The only drawback is that you don't necessarily have the various voltages offered by the PSC system if you need something other than 12V (I don't) -- unless of course, you're willing to wire in a bunch of sizeable voltage regulators -- and, of course, that you have to do all the work yourself, rather than simply pay someone and have a shiny box show up ready to go.  I built a new power distro for use with this system right before my current project, and it really took the bulk of a weekend (plus time to gather all the parts).  None of it is particularly challenging work, but it is tedious and time consuming.  That was unfortunate, but it allowed me to really customize the distro with the right number of outputs and tailored fuse protection for everything on the cart.

Yes, exactly. The regulated DC power supply (I can also post some links to the ones I have used, both linear - heavy! and switching) is connected to the battery terminals and the also the distribution to the cart to the same terminals. So, in essence when the regulated DC supply is "on" the equipment (the load) AND the battery are being fed 13.8 vdc. This works out to not be exactly like powering the equipment directly off the power supply because the battery is connected also and serves as a big buffer lessening any AC ripple that could come through. I did do one supply where I put a diode between the battery and the power supply so that when not in use DC would not flow back into the power supply. I don't do that anymore but I do have a breaker/fuse/switch so that when cart sits for weeks and weeks not working I can disconnect the power supply from the battery.

Regards,  Jeff Wexler

[Mick]

I'm not sure if I'm being redundant here, but I have two sealed 50 amp/hr L/A batteries in a custom built box which feed two PSC power max DC distributors. Separate outs for 6, 12 and 18 volt equipment. Seamless switching when the AC is disconnected and constant charging when connected. Works like a charm and gives me a minimum of 8 hrs on DC. (I've never had to run the system long enough to see exactly how long it will supply uninterrupted DC.)

[Jeff Wexler]

What Mick describes here accomplishes approximately what my supplies do but uses a product, from PSC, that one needs to purchase (but you are relieved of the duty of building something yourself). Also, Mick's setup has way more battery capacity than I need (with the accompanying weight to the cart as well) so I stick with basically 1 30 aH battery. I don't have the need for multiple voltages so my regulated power supply (10 to 15 vdc adjustable) works just fine. I will post some pictures of the cart power supply box I am using now.

Regards,  Jeff Wexler

[Bob Marts]

Jeff, Noah et al,

How far down do you use your battery alone before you recharge it on a conventional charger?

I've used the battery / Tripp Lite combo for about 8 years and it's very nice to not worry about a kick-out or lack of AC.  But after using the battery alone, I'm not sure when to leave the battery on this system or put it on a charger to bring it back up.

Bob Marts

[Jeff Wexler]

Jeff, Noah et al,

How far down do you use your battery alone before you recharge it on a conventional charger?

Bob Marts

Excellent question. In real world working experience if I have been on battery alone for any length of time and it gets down to 10.5 to 10.0 vdc, I stop using that battery (because the equipment will be at the bottom of its voltage range and might quit at any moment). So that battery might be put on a conventional external charger with no load on the battery, OR, I have just powered up the cart power supply (with its regulated DC power supply) and let that supply "charge" the battery. In those instances I might be reluctant to also ask the cart power supply to operate the equipment (the load). The scenario that I referred to really was the situation where the battery is seriously discharged, maybe down to 4 or 5 volts (wouldn't power any equipment anyway) from just sitting --- then I would definitely use a charger to bring it up to full before letting the regulated DC supply float across.

Regards,  Jeff Wexler

[Noah Timan]

Jeff, Noah et al,

How far down do you use your battery alone before you recharge it on a conventional charger?

It's been so long since I've had to charge it indivdiually, since we almost always have power on set for everything but the most brief of circumstances -- the last time I can remember running it down low enough to require a recharge was when I used it with a 12V air compressor when my car had a flat!  As Jeff notes, getting it under 11V is bad for the battery (and may cause the gear to fail in action). 

[S Harber]

I am running the DC supply over a pelicanized gel cell and the system has served me well.

Looking into the Optima AGM batts.

Presently I am using the Astron 20A switching DC supply after running the heavier linear versions for a few years.

What DC supplies are you all using out there and are there issues using the switching vs. the linear versions?

Scott Harber

[Jeff Wexler]

Presently I am using the Astron 20A switching DC supply after running the heavier linear versions for a few years.

What DC supplies are you all using out there and are there issues using the switching vs. the linear versions?

Scott Harber

I have used quite a few of these in the past (when not using linear supplies)

< http://www.trcelectronics.com/Meanwell/rs-150-12.shtml >

The switching vs. linear is something to consider as everyone seems to understand that the linear supplies (with big transformers, heavy and producing a lot of heat) are definitely superior, the switching supplies always have the potential for trouble (but they are light and cool running). Providing you get a fairly well rated (noise spec, etc.) supply, the issue is still the possibility of interaction amongst the various components that have DC to DC converters as part of their power supplies. I have found the only true test is to get one of these switchers and power up all the equipment it will be powering and listen for noise. Then go for it but realize that if you add another device to the cart, something new, you need to evaluate that. Also, when testing any given supply with your equipment, be sure to hook it all up WITH the battery in line as well --- the battery serves as a big buffer that irons out many potential problems that could be present if you powered the equipment directly off the supply.

Regards,  Jeff Wexler

[Matthias Richter]

if using a sealed lead acid battery one shouldn`t discharge it lower than 10.5V Anything lower than that will damage the battery. AFAIK (and have experienced) 5V means the battery is dead and won`t come back to life (12V)

Matthias