×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Buying the right power pack

Buying the right power pack

Buying the right power pack

(OP)
I am going to be buying a Roland CD-2e recorder and using it in locations where I cannot plug it in.

The tech specs of this unit tells me that it has a current draw of 540 mA, and when using batteries it takes 6 X LR6 (AA) type alkaline batteries - so 9 volts DC, right?

The specs also say I cannot use the AA batteries for CD writing and reading, that the unit must use the AC Adapter.

Therefore I need a portable power pack sized to run this unit, full time, for about 12 hours per day, and then be able to plug it in over night and recharge it so it can do it again the next day, for 4 -5 days in a row.

Many of the power packs I see on the market have auto battery boosters cables, a light, a radio and other accessories, that I do not need, but I suspect I'll have to take. All I really need is the power pack that can be recharged and, I guess, the inverter to run the AC adapter.

Can you folks help me choose the right size of power pack and if you have any suggestions for a specific brand and model, I'd be glad to hear it.

I'd also consider assembling the parts myself into a suitable case, making my own power pack, but I suspect buying the ready made unit will be a lot simpler.

Thanks

 

RE: Buying the right power pack

Can't you run the unit on 9VDC and still run the drive?  You've only stated you can't run it on the measly AAs not that you can't run it on 9VDC.  It would be much better to stay in the DC realm.

What is the labeled OUTPUT of the adapter?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Buying the right power pack

(OP)
Yes a 24 Ahr battery, and an inverter, and a battery charger will do the job. And, i'll probably end up with an off-the-shelf power pack.... my question was what size power pack should I get?

As for staying in 9 volts DC, that would be the most efficient, wouldn't it.  The Roland site does not tell us the OUTPUT of the adapter, and I only assume its 9 VDC. I have a friend who has one of these units and I'll get them to check.

But again, if I stay in VDC, I'll still have to buy an additional charger.

I'm looking at a unit available locally and I'll probably get it unless one of you experts points me elsewhere. Its this unit:

http://www.canadiantire.ca/AST/browse/4/Auto/SolarPortablePower/PowerPacks/PRD~0111823P/Eliminator%2BPowerBox%2B800.jsp

Thanks very much for all your help. I love forums.

 

RE: Buying the right power pack

If you go the inverter route you should try to get one that is twice the AH your device really needs as you wil be suffering double conversion losses and getting a pack that provides about the energy demanded means you will be over discharging your batteries. B A D L Y.  Expect about 10 cycles before failure. Also expect capacity shortage starting about the 5th cycle.

You need at least twice the required AH. This is why you want the efficiency as high as you can get it because you also need twice the capacity demanded by those inefficiencies.


Look at this: http://www.powerstream.com/daa-1209.htm

You need 540mA x 9V = 4.9W

converter 70% efficiency => 7W

7W/12V = 0.6A

0.6A x 12hrs = 7.2Ah/day

If you charge every night then you should use a 14.4Ah or larger battery.
Common LA size is 17Ah.
See:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P174-ND

An excellent charge is found here:
http://batterytender.com/battery-tender-plus-12v-at-1-25a.html

 

Keith Cress
kcress - http://www.flaminsystems.com

RE: Buying the right power pack

(OP)
Now you have me interested in building it from parts... I needed a project!

The battery you mentioned is the Panasonic P174-ND and weighs 14.3 lbs.

The converter only weighs 7 oz. and charger is 3 lbs, so all the parts, plus cables, etc will not exceed 20 - 25 lbs. I can lug that to where its needed easily.

I'll be looking locally for a sturdy, rugged, tool box or something like that, in which I can mount the parts.

Thanks for your help. As the project continues, I'll take some pictures and share them with you.

 

RE: Buying the right power pack

(OP)
It just occurred to me... is there any special need for ventilation for the battery, converter or charger?

In use, the battery and converter will be in a building at a trade show.... a convention center.

I see the battery is sealed, so I assume if I carry it at a shallow angle from time to time, it won't damage anything.

When charging, the setup will likely be in a hotel room, getting charged for the next day's work.

Any special environmental issues I should know?  Fumes? noise?

Thanks
 

RE: Buying the right power pack

(OP)
Ok, more questions...

If I put all these parts into a carrying box of some sort and hook them up together, will they conflict with each other?

The converter is wired to the battery, and so is the charger. Is there any risk of damage to the converter while charging? Is there any risk of damage to the charger while using the battery/converter combination connected to the recorder?

Or will I have to disconnect one element while using the other?? If so, I guess some sort of switch might be handy.

Thanks

 

RE: Buying the right power pack

Most batteries will generate hydrogen during charging, so good ventilation is a must.

Your circuitry should be disconnected from the battery during charging.  A typical charger will put out several volts above the battery nominal voltage to essentially "push" the power back into the battery.  The higher voltage could potentially damage the inverter, although it should be designed to handle the voltage range.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Buying the right power pack

In this case you should not have a problem hooking up the charger and leaving it hooked up.  It should not discharge the battery if the charger is unplugged but remains hooked up.

The DC-DC should even handle running while the charger is powered because the charger should not put out more than 15V which is the input rating of the DC to DC.

There should also be no hydrogen evolved in this case.  I would probably NOT ventilate the case unless it will never see rain.  Instead I would run it with the lid ajar.  Or you can ventilate it and not worry about it.

If you do ventilate it you want some holes near the bottom and some near the top.

You should certainly give it a test before your show.  You want to make sure things don't get too hot in the resulting box.

A tool box is a good idea that would allow easy handling.  It will also provide storage for the cords.

I would also add a fuse to your output, 1A.  So if the cord gets shorted you don't lose everything.

One last feature I'd add would be an in-line set of connectors.  The reason is for the unexpected. In a trade show you could easily have someone catch the cord with something. You want the plug to just un-plug not yank the device you're powering off onto the floor.  A straight in-line connector set will do this. The one in the device will invariably be at right angles to any pull and NOT automatically unplug.

Good luck.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Buying the right power pack

(OP)
Thanks guys... you have all been a great help.

I will follow up with info and pics as I get this going.

 

RE: Buying the right power pack

(OP)
In looking at the converter, I see another one offered by the same supplier... will it do the job as well? I see that its switchable allowing me to use this unit for other devices.

Thanks

http://www.powerstream.com/daa-1209.htm

RE: Buying the right power pack

(OP)
I cannot seem to make the link work for that page... the model number of the one I mean is PST-DC292.

Its the second or third one down the list.

Will that one work as well?

 

RE: Buying the right power pack

(OP)
"The time spent in reconnaissance is never wasted"...

I dunno who said it first, but it appeared several times in the books of one of my favorite authors, Ted Allbeury.

I've been mulling this whole project over in my head today and trying to come up with an idea for a suitable carrying case for it. I had planned originally to use a heavy duty plastic tool box, but in order for the battery to sit upright, I'd have to get a box that is quite long - 20 inches, or so.

So I cast around looking for a box that was sturdy enough to carry the battery and other parts, tall enough so it could stand upright, and with a handle on the top. And finally I discovered the ideal box - an ammo box! With the configuration detailed above, the 50 caliber ammo box will do the job well, I think. Here's a link to what I mean:

http://www.usmilitarysurplus.com/surpluscatalog/product_info.php?products_id=841

Should work well, no?

Then I started thinking about trade offs. Based on the design above, I'll be carrying this box back to the hotel every night and recharging the battery on the hotel plug in.

What would it take to have a setup that would last the whole show?

Typically;
Friday     12 hours
Saturday   12 hours
Sunday      8 hours

Total      32 hours

Then I went back to KC's calculations, as shown above, and tried to bend my head around it, using 32 hours and using the other multi-output converter.

Here's what I got:

9V @ 2.1A  =  18.9W

converter efficiency 73% X 18.9W  =  13.7W

13.7W / 12V - 1.14A

1.14A  X  32 hours = 36.5 Ah

Double that = 72 Ah and that equals a BIG battery or two smaller ones. I abandoned my math calculations there, and I now assume that if the previous battery is 20 lbs weight, this new configuration is probably going to weight 50 - 60 lbs, more than I want to lug in. I'd probably end up with some sort of wheeled dolly arrangement - just not worth the aggravation.

So, KC, I'm staying with our original design and I'll be carrying the unit back to the hotel Friday and Saturday nights to recharge it.

Can I have your input, comments and suggestions?

Thanks

PeterAL



 

RE: Buying the right power pack

Fine.  Just one adjustment.

Gelcells can run in ANY position. So stop worrying about keeping the battery upright.

Now can you use a smaller toolbox?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Buying the right power pack

(OP)
Ahah!!!

 

RE: Buying the right power pack

(OP)
Yeah, I'm not surprised my math was wrong...

Thanks

 

RE: Buying the right power pack

(OP)
Ok, job done!

Thanks to you folks, I have a neat little portable power supply for my device. This will give me more flexibility in my work and make life easier.  Thanks so much for all your help.

If you have any questions about the components I ended up using, or anything else about this project please feel free to ask.

Here's an album of pictures of the various steps I took.

http://good-times.webshots.com/album/575506569UBMmTm]

 

RE: Buying the right power pack

(OP)
Total cost?

Ammo Box     $20.00
Spray Paint    5.00
Battery       50.00
Charger       45.00
Converter     40.00   (included $22 for shipping to Canada!)
Small parts   25.00
          ----------
Total        185.00

I could have got a power pack for somewhat less at the local Canadian Tire store, but I really enjoyed doing it myself.

Thanks



 

RE: Buying the right power pack

Looks pretty good!

Don't try to take it on an airliner...

One point. You obviously have no idea how much energy that battery actually represents
or you would immediately fashion some sort of covers for the battery terminals.
 

Keith Cress
kcress - http://www.flaminsystems.com

RE: Buying the right power pack

(OP)
Covers?  Covers?  You mean to guard against shorting out between the two?

Hmmm.. it would be nice if there was some sort of material I could heat shrink around the terminals like I did with the joins in the wire..

I'm gonna look for large diameter heat shrink stuff..

Thanks

 

RE: Buying the right power pack

Yes that is what I mean. Having open posts at the bottom of a carrying case invites something metallic connecting them someday.  It could well be during transit in the trunk of a subsequently burning vehicle.  :)

Keith Cress
kcress - http://www.flaminsystems.com

RE: Buying the right power pack

(OP)
Yes indeed.. makes sense...

 

RE: Buying the right power pack

(OP)
Well, an update... this battery system you folks helped me design has worked well... very well.. In fact it seems to be so good, that I suspect that it might carry on for the whole three days we need it, rather than recharging at night every day.

But, I don't want to take chances and be without power when needed.

I use it 12 hours straight, with stops for a minute or two, every half hour. Then I would not need it until the next day for another 12 hours stint, and the similarly the third day for about 10 hours.

If this battery will last throughout the whole three days, it will save me lugging it back to the motel every night for re-charging. It heavy enough, I'm considering re-working it into some sort of wheeled cart.

So, my question is, is there a gauge I can put on the battery, preferably wired right onto it, to tell me how much is left in the battery?

Thanks for your ongoing help.

 

RE: Buying the right power pack

There is probably something out there... Whatever it is it will draw from the battery constantly. This means it will help your battery die in storage.

You could just measure it with a voltmeter.  12V is dead flat - damage land.  13V+ is charged.

However I suggest you go for the exercise of recharging it as running the battery down below half of its capacity and letting is sit overnight will permanently reduce its capabilities.

I'm surprised you can't find an outlet somewhere nearby that you can charge it at.  Not maybe where you use it but still local, even while you're eating lunch or something. The first few minutes really pack on the recharge.

Keith Cress
kcress - http://www.flaminsystems.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources