circuit to replace battery

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Volter
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circuit to replace battery

Post by Volter » Tue Dec 16, 2014 2:27 pm

I would be interested to know what it would take to replace a 5000mAh, 3cells at 11.46V battery with circuit run off 120V that would be used for testing, so, keeping the battery out until needed. Would someone have an idea what I need for that? :!:
Thanks much.

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Lenp
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Re: circuit to replace battery

Post by Lenp » Tue Dec 16, 2014 3:09 pm

A regulated bench power supply might be more flexible and less expensive than a DIY project.
0-30V / 5A metered, regulated V & I ..around $60 online!
Len

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"I must be on the way to success since I already have the junk". (Me)

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jwax
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Re: circuit to replace battery

Post by jwax » Tue Dec 16, 2014 3:47 pm

Rather depends on how much current you really need at any one time.
If current demand is low and/or infrequent, a 12 VDC, 1 Amp wall wart maybe all you need. It would basically just keep the battery fully charged, but it all depends on your current demands.
Where did you get a 11.46 volt battery? :)

dyarker
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Re: circuit to replace battery

Post by dyarker » Tue Dec 16, 2014 4:49 pm

The amphour rating of the battery would be a more useful clue if we knew how long a full charge (when the batteries were new) kept the whatever it is running.

Out of curiousity what chemistry battery/cell has about 4V out? (3 for almost 12V)
Dale Y

Volter
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Re: circuit to replace battery

Post by Volter » Wed Dec 17, 2014 9:41 am

Well, it is the LIPO battery that runs the propeller motors. 5000mAh 35-70C discharge, 3 Cell 11.1V. For testing I would like to avoid hooking up and disconnecting the battery, it has to be recharged so often!
Thanks.

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Externet
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Re: circuit to replace battery

Post by Externet » Wed Dec 17, 2014 10:31 am

As mentioned by Lenp; a regulated power supply is a convenient way, bought or built, set to your requierements.

A fixed supply in parallel to the Lipo, set at its pack charging voltage will work well too. Will 'float' to recharge the pack and supply the motor. Measure the existing charging supply to set the correct voltage, perhaps the existing charger will suffice without building an extra.
- Abolish the deciBel ! -

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jwax
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Re: circuit to replace battery

Post by jwax » Wed Dec 17, 2014 11:53 am

Well, we now know that it will be used to run "the propeller motors", so that's a start!
Measure max current draw, and select one of hundreds of 12 volt wall warts to supply that amount of current.

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haklesup
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Re: circuit to replace battery

Post by haklesup » Wed Dec 17, 2014 1:59 pm

I agree that knowing the capacity of the battery is not sufficient to know the load of the propellers. If you don't want to measure current directly, how about giving us an idea of how fast the batteries die. Ideally a 5Ah battery would run for 1 hour if the load were 5A, however with efficiency losses, you don't quite get that much. I am guessing that by your comments, it lasts much less than one hour making the load 5A to 8A in my guesstamation. I would also guess you are using 3x LiIon cells at 3.8V to get the 11.5V. LiIon being light and high energy density is the best chemistry for model airplanes though you may be using Li-Polymer instead (flat cells vs cylinders).

You probably don't need much regulation given your load seems to be a permanent magnet motor run from a battery which will change in voltage as it depletes. You could probably run the whole show off a plain old car battery charger in the fast charge mode (10A, 12V). If you felt you needed regulation or variability, you could add a bank of 5 parallel LDO regulators on a heatsink and maybe a big capacitor across the output. A 12V car battery charger could probably be connected in parallel with the battery in the 2A maintenance (trickle charge) mode and you would not have to disconnect the batteries. On a plus side, you would charge them when the load is not running.

If you do this often, then maybe investing in a variable bench power supply would not be a bad idea. Again, pay attention to max current to know you can power your load without clipping the power. Batteries are nice that way in that they can deliver very large current when needed (at the cost of discharging sooner)

Volter
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Re: circuit to replace battery

Post by Volter » Wed Dec 17, 2014 9:52 pm

At full throtle the battery lasts about 10 -12 minutes!

dyarker
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Re: circuit to replace battery

Post by dyarker » Thu Dec 18, 2014 6:45 am

10 minutes = 1/6 hour = 0.166667hour
5000mAHr = 5 AHr
5 AHr / 0.166667Hr = 30A

No wall wart is going to handle that. Makes haklesup's suggestion look good. Or, a large 12V switching supply.

Cheers,
Dale Y

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dacflyer
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Re: circuit to replace battery

Post by dacflyer » Thu Dec 18, 2014 9:59 am

i have a 5 volt - 50 amp PS, but i see you need 12v...

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jwax
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Re: circuit to replace battery

Post by jwax » Thu Dec 18, 2014 1:46 pm

I'm curious as to why you need to run the motors, on the bench, for more than ten minutes.
BTW, how many motors are there?

dyarker
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Re: circuit to replace battery

Post by dyarker » Thu Dec 18, 2014 5:44 pm

I don't think he was running on the bench that long. I asked how long a full charge lasted so I could estimate current draw from amphour rating of the battery.
Dale Y

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haklesup
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Re: circuit to replace battery

Post by haklesup » Fri Dec 19, 2014 1:23 pm

Most chargers I have seen are 10A/2A but I looked at Wally Mart and they have a "Schumacher 75/12/2 Amp Fully Automatic Starter/Charger with 2 LEDs " that should be up to the task for $56 and Diehard 75/12/2 Amp Fully Automatic Battery Charger with Emergency Engine Start for $49 plus other selections. The 75A mode is for starting cars (and not continuous duty) but it will definitely hold up your props no problem at 20A. If you need more power, you are into 150A or more chargers with integrated wheels and cart handle. In the middle the battery based jump start kits should also provide additional capacity with extended cordless operation compared to your cells.

marc4g
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Re: circuit to replace battery

Post by marc4g » Fri Jan 02, 2015 12:13 pm

One option you may want to consider is a new or used ATX power supply. I got one at Good Will for $3.00. If you want a new one, the cost may go up to $30 or so. The smallest ATX supply should give you more than enough current.

There are all sorts of wiring diagrams for these things on line.

I just hacked off all of the wires except for the 0v, 12v and /enable control wires, ran the 12v power thru a fuse and that was about it.

If you wanted the thing to just power up, you could just attach the '/power' control wire to 0v and use a power strip to control the application of 120v from the wall.

If you elect to just tie the '/power' to 0v however, you will loose some options

The nice thing about the '/power' control is that you can use almost anything to turn the ATX on and off. A low power transistor such as a 2n2222 an opto isolater, etc. etc.

The ATX supplies also have an output that is normally at 5v and goes to 0v if the power supply is not ok.
I found that to use this logic level it is best to run it thru a logic gate as it did not seem to be able to support much loading. I used this output to drive a led to tell me if the ATX is on or not.

The 5v standby output is also nice as it outputs 5v even when '/power' control is at 5v and 120vac is present.

Tying the '/power' permanently low would make the options impossible without using another power supply.
Which would be kinda dumb.

Marc

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