Author Topic: IC That Will Indicate When I Have Low Battery  (Read 2280 times)

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Offline billhowl

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Re: IC That Will Indicate When I Have Low Battery
« Reply #30 on: November 20, 2011, 07:39:38 AM »
For SLA each cell had max voltage of 2.45V, hence 24V batteries can go up to 29.4V, so calculate your resistor values base on 30V.

Offline SylvestreTopic starter

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Re: IC That Will Indicate When I Have Low Battery
« Reply #31 on: November 20, 2011, 03:36:29 PM »
Ok here are my new calculations

Resistor 1: 16500 Ohms
Resistor 2: 3300 Ohms

3300/19800=.16666666667

.166666666666667*30= 5 volts

30/19800= 1.5 ma wasted

I'm not sure how to choose a power rating for the resistors.  I have two motors that run at 400 watts each.  Does this mean I have to get a +800 watt rated resistor?
« Last Edit: November 20, 2011, 03:40:15 PM by Sylvestre »

Offline billhowl

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Re: IC That Will Indicate When I Have Low Battery
« Reply #32 on: November 20, 2011, 05:21:08 PM »
Calculate for Power (P)
P = I 2 x R
P = 0.00152 x 19800
P = 0.04455W

So power rating for the resistors you can get 1/8W (0.125W) or 1/4W(0.25W)


Offline SylvestreTopic starter

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Offline billhowl

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Re: IC That Will Indicate When I Have Low Battery
« Reply #34 on: November 20, 2011, 09:00:29 PM »
The first one 16,5K was okay, but the 3.3K need not to have 3W, this will do

http://www.mouser.com/ProductDetail/Xicon/271-33K-RC/?qs=sGAEpiMZZMu61qfTUdNhG%2fJtDnsRrrptaPf%2fpx2qOkY%3d

Offline SylvestreTopic starter

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Re: IC That Will Indicate When I Have Low Battery
« Reply #35 on: November 20, 2011, 09:04:57 PM »
Wow thank you!  I must have overlooked that on accident.   :P

Thanks a lot!

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Re: IC That Will Indicate When I Have Low Battery
« Reply #36 on: November 25, 2011, 11:10:58 AM »
If I am hooking up my two sealed lead acid batteries in series to produce 24v, will I get a little over 24 volts?  Should I recalculate my resistor values for 24 or 25 volts?
Best to measure with a multi-meter the total fully charged voltage. But it'd definitely be more than 24V for sure.

Offline SylvestreTopic starter

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Re: IC That Will Indicate When I Have Low Battery
« Reply #37 on: November 27, 2011, 07:58:33 PM »
I would hook it up to a multimeter, but my multimeter is only rated for 10 amps while battery (two batteries in series) is 24 volt at 50 amp. :(

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Re: IC That Will Indicate When I Have Low Battery
« Reply #38 on: November 27, 2011, 08:17:17 PM »
I would hook it up to a multimeter, but my multimeter is only rated for 10 amps while battery (two batteries in series) is 24 volt at 50 amp. :(
When you measure the battery, there should be zero amps. You're only measuring voltage.

Measure each battery individually, then add the two voltages to get the total.

Offline SylvestreTopic starter

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Re: IC That Will Indicate When I Have Low Battery
« Reply #39 on: November 28, 2011, 12:08:01 PM »
Oh ok I did not realize that.  Thanks!

 


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