DC current electrical question

Huntindave McCann

Huntindave McCann

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I have a question for the brain trust here on TDBP.

Situation, Setting up an sonar device to be powered from two separate power sources. (Either a 14.8 volt lithium battery or a 12.0 volt lead acid battery.) Only one power source to used at any one time. but do not want to drop the voltage when switching power sources. I wish to keep the sonar unit up and running when making the change of power sources.

At first, I had planned to use a single pole double throw to select the desired power source. Then I realized that there will be a momentary loss of any power as the switch is thrown from one position to the other. I am afraid this momentary loss of power will shut down the active sonar unit, necessitating a restart of the sonar unit. I do not wish to have a restart.

Plan "B" is to have two on/off switches (one from each power source). Operation would be as follows;
(1) select power source ie, switch "A" on (switch "B" off)
(2) turn sonar unit on with built in power button
(3) While sonar unit is up and running, switch to secondary power source by 1st switching "B" on (at this time both power sources are "on") followed by switching "A" off.

I'd like to make this a fool proof one step operation with uninterrupted power switching. I can't leave both power sources connected all the time because there is a 2 volt difference in the batteries I will be drawing from. The voltage range for the sonar unit will accommodate either voltage.

Is there a device I can use to maintain voltage to the sonar unit, while throwing a "single pole double throw" selector switch.

Suggestions?



View attachment LowranceShuttle3_1024x1024@2x.webp



elite-bag.jpg



SWITCHPLATE002.jpg


Ther above switch panel just fits in the opening to the right of the 32 amp hour lithium battery. I have room for a voltmeter/USB fixture in the middle surrounded by up to four on/off switches that are 23mm in diameter.

Everything I have found so far is, 3 Position ON1-OFF-ON2 . What I need is, 3 Position ON1- on 1&2 -ON2 only need a 7 amp rating.


20220326_190817.jpg
 
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A four position battery switch, batt 1, 1+2, 2, off, won't do it? I don't remember there being a dead spot when switching, but maybe my electronics aren't that sensitive.
 
Thanks,
I think you are right however; I don't have the room for one of those. I will do some research on that though. I'll add a photo to the original post, of what I am dealing with.
 
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Edited: OK, I see the 32 amp hour mini battery. You obviously have a very specific set of conditions where you want to be able to do this, which I don't fully understand. I'm all for you getting just what you want!
 
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It's not an uncommon requirement in machine control circuits. Look for "make-before-break" contact sets.
I have used them in control relays, but I seem to recall they also offered them in pushbutton and selector switches as well. Allen Bradley stuff is really pricey, but it can had on eBay for reasonable money. Admittedly, it's been quite awhile since I needed such things, but it's worth checking out.
 
tod osier said:
Edited: OK, I see the 32 amp hour mini battery. You obviously have a very specific set of conditions where you want to be able to do this, which I don't fully understand. I'm all for you getting just what you want!
Click to expand...

Tod,
Yes,,,,,,,,,,,,,,, I want my cake and eat it too! [cool] [cool]

That "mini" 32 amp Lithium battery packs a lot of energy in a small lightweight package. The entire self powered sonar "shuttle" is designed to be 100% portable. I can use it when ice fishing. I can use it in a canoe. I can also use it in my power boat which has it's own 12 volt electrical system.

This sonar system is actually a power hog given the amount of electronics it houses. In order to conserve the energy stored in the 32 amp lithium battery, I would like to tap into the boats electrical system when the engine is running and only when the engine is running. This will require a smooth uninterrupted transfer from the 32 amp battery source to the boat electric source and back again as and when needed.

To compound the situation, the 32 amp battery is 14.8 volts while the boat battery is 12 volts. Thus if I leave both voltages tied together for any length of time, the voltages will attempt to equalize, prematurely draining my 32 amp Lithium battery .

Another consideration is that 14.8 volts is better for the electronics (and quality of the information being displayed) over 12 volts. When the engine is running and the alternator is in play, I should be getting 13.5 to 14 volts.

Again the goal ; In order to conserve the energy stored in the 32 amp Lithium battery (for times when the engine is not running and times when I cannot recharge overnight on 2 or 3 day trips) I will NOT be able to recharge the Lithium from the boat system. The charger for the Lithium charges at 16+ volts.

BTW; Your concern is duly noted and appreciated. Always nice to have your blessing. [w00t]
 
Gordon Bartlett said:
It's not an uncommon requirement in machine control circuits. Look for "make-before-break" contact sets.
I have used them in control relays, but I seem to recall they also offered them in pushbutton and selector switches as well. Allen Bradley stuff is really pricey, but it can had on eBay for reasonable money. Admittedly, it's been quite awhile since I needed such things, but it's worth checking out.
Click to expand...

Gorden,
Thanks, always nice to have the correct "search terms". I will do some checking. Yes I did see some rather bulky switches with some rather expensive prices when I did my original research. Just kind of passed them over but will go back and take a closer look. Thanks again for steering me in the right direction.
 
Just a suggestion but try to disrupt power and restart maybe you will not lose what you have on the instrument.
 
I would think you could recharge the lithium battery from your boat battery pretty easily. Just buy a 12V to 110V converter and plug the lithium battery charger in it just like you plug it in at home to recharge.

And can you run that sonar unit while plugged into a 110V outlet while recharging the battery? There would be your dual source uninterrupted power if you could. I know my Marcum sonar I can use while charging the battery.
 
John Ki said:
Just a suggestion but try to disrupt power and restart maybe you will not lose what you have on the instrument.
Click to expand...
John,
Anytime the voltage is removed from the sonar unit, it has to be restarted, which involves a power up cycle and reacquiring a satellite lock. Some guys have an issue with their sonar units installed in their boats. Every time they go to start their main motor, they get a momentary voltage drop and lose their sonar so they resort to a dedicated battery just to run the electronics. I had this same issue with the GPS on my ATV, until I installed a larger battery.
 
Mark W said:
I would think you could recharge the lithium battery from your boat battery pretty easily. Just buy a 12V to 110V converter and plug the lithium battery charger in it just like you plug it in at home to recharge.

And can you run that sonar unit while plugged into a 110V outlet while recharging the battery? There would be your dual source uninterrupted power if you could. I know my Marcum sonar I can use while charging the battery.
Click to expand...

I don't believe the alternator on my boat motor will handle a 110Volt invertor. Even if it did, the charger would be connected to the lithium battery ahead of the "power source selector switch". So there would still be an interruption of power when switching power sources.
Thank you for your thoughts.
 
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Ok was just reading your first post and it stated you were afraid it might affect it but I guess you know it will.
 
It's been a long time since electrons school, but would a capacitor placed in parallel on the sonars power leads act as a power supply when you switch batteries?
 
MIKE-SID said:
It's been a long time since electrons school, but would a capacitor placed in parallel on the sonars power leads act as a power supply when you switch batteries?
Click to expand...

Mike,

That was one option I had been wondering about, but lack sufficient knowledge on the how's and why's of setting up something like that. Still gathering info.
 
Huntindave McCann said:
Mark W said:
I would think you could recharge the lithium battery from your boat battery pretty easily. Just buy a 12V to 110V converter and plug the lithium battery charger in it just like you plug it in at home to recharge.

And can you run that sonar unit while plugged into a 110V outlet while recharging the battery? There would be your dual source uninterrupted power if you could. I know my Marcum sonar I can use while charging the battery.
Click to expand...

I don't believe the alternator on my boat motor will handle a 110Volt invertor. Even if it did, the charger would be connected to the lithium battery ahead of the "power source selector switch". So there would still be an interruption of power when switching power sources.
Thank you for your thoughts.
Click to expand...

I talking about the real simple plug into a 12 volt cigarette lighter and then charge your sonar
 
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