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Author Topic: Floating Battery  (Read 4396 times)
N4DSP
Member

Posts: 158




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« on: March 22, 2014, 09:19:53 AM »

If any group would know this it surely would be the QRP forum!

Have an Astron Power Supply RS-35M and my battery is a Power Sonic
36aH 12volt. I want to float charge it. I use Anderson Power Connectors.

Plugging the battery into the 25amp circuit of the RIGrunner which is connected
to the Astron Power Supply all that is required to float charge it?

What voltage must be maintained?

Thanks

john
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AA4PB
Member

Posts: 12896




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« Reply #1 on: March 22, 2014, 09:47:57 AM »

A 12V lead-acid battery will float charge at 13.8VDC. There are a couple of issues with connecting it directly across a 13.8VDC power supply. If the power supply gets shut off or looses primary power the battery may discharge back through the input of the power supply which can potentially damage the supply. A series diode is often used to prevent this back-flow of current. A silicon diode however drops about 0.7V in the forward direction so the power supply voltage needs to be increased to 14.5V in order to compensate for this drop. Schottky diodes and FETs will have a lower forward voltage drop and may be a better choice.

The other issue is that if you connect a fully discharged battery across a 13.8V source, the battery can draw a considerable amount of current until it obtains some charge. Automatic battery chargers contain a current limiter in order to prevent this. The heavy current is more likely to damage smaller batteries like a 7AH than a large capacity battery and of course doing it on a regular basis is more severe than occasionally.

Here's a link to a safe solution: http://www.westmountainradio.com/product_info.php?products_id=pg40s
« Last Edit: March 22, 2014, 10:45:21 AM by AA4PB » Logged
N4DSP
Member

Posts: 158




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« Reply #2 on: March 22, 2014, 11:53:50 AM »

Thanks for the info Bob.

john


A 12V lead-acid battery will float charge at 13.8VDC. There are a couple of issues with connecting it directly across a 13.8VDC power supply. If the power supply gets shut off or looses primary power the battery may discharge back through the input of the power supply which can potentially damage the supply. A series diode is often used to prevent this back-flow of current. A silicon diode however drops about 0.7V in the forward direction so the power supply voltage needs to be increased to 14.5V in order to compensate for this drop. Schottky diodes and FETs will have a lower forward voltage drop and may be a better choice.

The other issue is that if you connect a fully discharged battery across a 13.8V source, the battery can draw a considerable amount of current until it obtains some charge. Automatic battery chargers contain a current limiter in order to prevent this. The heavy current is more likely to damage smaller batteries like a 7AH than a large capacity battery and of course doing it on a regular basis is more severe than occasionally.

Here's a link to a safe solution: http://www.westmountainradio.com/product_info.php?products_id=pg40s

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ZENKI
Member

Posts: 960




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« Reply #3 on: April 11, 2014, 06:15:39 PM »

Just buy one of the CTEK smart chargers. Its one of the best chargers/conditioners for batteries. They also cause no interference because they  have proper
EMC approvals. You can connect one of these to your battery and come back in 10 years and your battery will be still good.

http://www.ctek.com/

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N7ROX
Member

Posts: 3




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« Reply #4 on: April 11, 2014, 08:45:31 PM »

Just buy one of the CTEK smart chargers. Its one of the best chargers/conditioners for batteries. They also cause no interference because they  have proper
EMC approvals. You can connect one of these to your battery and come back in 10 years and your battery will be still good.

http://www.ctek.com/



Second vote for the CTEK charger.  I keep them on my toys and cant remember the last time I had to change a battery in one of them!

Craig
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LA9XNA
Member

Posts: 109




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« Reply #5 on: April 19, 2014, 03:31:53 PM »

Be carfull  with the CETIK chargers they have harmonics in the 2m hand
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ZENKI
Member

Posts: 960




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« Reply #6 on: April 23, 2014, 05:51:57 PM »

News to me. I just checked my 5 amp and 10 amp with the Kenwood HT AM and SSB I cant find any.

I will check with the spectrum analyzer and report back.

Be carfull  with the CETIK chargers they have harmonics in the 2m hand
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KU7PDX
Member

Posts: 54


WWW

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« Reply #7 on: April 25, 2014, 08:50:51 AM »

This website has a lot of great information on charging batteries of many different chemistries (along with a lot of other info): http://www.powerstream.com/tech.html
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73,
Chris - KU7PDX
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