Why is taking 12v from one batt bad?

[SoundGuy]

I have a 9000 Lbs winch and a 12VDC inverter running off the front battery, I feel the thread comments are correct about the even charge rate, but you only use the winch, what 3-4 times a month and the inverter very little and 200 watts for lights is nothing when you have a 100 Amp alternator running. I am also confident you will drive the truck often so the battery's will always be charged anyway, I think you will be OK, Just my opinion.

Just for what is is worth. Figuring in for the inefficenties of Inverters if you are drawing 200 watts then you are pulling close to 20 amps off of that battery. With a 100 amp alternator or not, you are still overcharging on battery in the chain?

 

[SoundGuy]

Oh and just a quote note. I know this has been beat to death, but some of you may be wondering if your batteries are balanced or not. The is two meathods to find out. One is kinds complicated and involves drawing current for a set amount of time. The second is my preferred methon because it is simple. With the engine off and the lights on (or some sort of load on both of the batteries) use a volt meter to measure the voltage on the batteries. They should be pretty close to each other. I try to keep mine within 0.1 volt. In reality 0.2 is probably ok.

The best way to correct batteries that are not ballanced is to remove all cables connect both batteries together with very good connection ( positive to positive and negative to negative)and then connect a 12v charger to one of the batteries positive leads and the other batteries negative lead. Let it charge like that for a while and you should be good.

Just another note, if the battey voltages appear the same until you put a load on it and with a load one drops way low' this is a sign that you have a bad battery. There are methods of making due but the real solution is to replace the batteries.

 

[ratat98]

12v revisited

Ok instead of starting a new thread I just figured I would continue this one.

I have a Pyle 24-12v convertor now and I want to hook it up to charge a seperate third battery to run 12v accessories off of...how do I go abouts doing this? Do I need a battery charger between the convertor and the battery? Can I ground the 12v to the frame without frying something, or do they need a separate ground?

 

[SMOKEWAGON66]

Ive ran a CB off one battery since I got the deuce home last year. I have yellow top Optima deep cycle batteries in there (expensive) and have only had them go dead one time (left the panel lights on) Its just a stock barefoot radio so there is no heavy draw. If i get 2 years out of these same batteries, ill be happy. If not...oh well thats life. Ive used the single battery for 12v (CB radios only) on several trucks throughout the years and have never seen any noticeable difference in battery life, so for me the setup is fine. But i agree that if your going to draw a heavier load, then put in the converter/additional alternator/etc.

 

[Heath_h49008]

I'm curious why you wouldn't just pull a parallel 12v off both batteries to ensure an even load and be done with it. Current wise, the batteries don't know if you're yanking 12v or 24v...

Nevermind... I just thought about what that would entail, and what potential failures would be.

Converter.

 

[Stalwart]

Heath, you could try that but you'd end up with burned wires and smoke. You can parallel 2 batteries OR you can have them in series. You CANNOT have them wired both at once without some circuits YOU nor I will not be able to build or design. No offense Dude, but if you ask this question you need just a little more information so as to why it can't work. It's beer time and I'm not gonna write a book. This question has been asked and answered many times before.

 

[Heath_h49008]

Heath, you could try that but you'd end up with burned wires and smoke. You can parallel 2 batteries OR you can have them in series. You CANNOT have them wired both at once without some circuits YOU nor I will not be able to build or design. No offense Dude, but if you ask this question you need just a little more information so as to why it can't work. It's beer time and I'm not gonna write a book. This question has been asked and answered many times before.

The circuits aren't that complex... just break the dogbone connection before you close the switch to the 12v system/12v battery/12v solar/maintainer. But it's ugly if you flip switches the the wrong order and more expensive than just running a converter... You must have just missed my edit.

 

[Stalwart]

Yes dear, or a battery equalizer That way you could continuously draw both 12V and 24V and NOT have an imbalance of battery draw, and both batteries could be charged equally with 28V supply. Goodnight!

 

[Bob USNR]

If you are not going to use large load devices, and don't really want to install extra equipment, you can get IC chip regulators that can reduce the voltage to what ever you need. Make sure you use regulators that can handle twice the load you need.
Once assembled these devices can be installed in less than an hour. It should be smaller than a pack of cigarettes.
And if OEM appearance is an issue paint it od green and only the really informed should ever notice it.

I hope you know that 12vdc and 28vdc are not the actual voltage of the systems.
Your regulators should be set at 12vdc = 14.5vdc and 24vdc = 28vdc. Both are + or - 1/2 volt.

You can get the parts at any good electronics supplier. Radio shack may still carry them.

e

 

[ratat98]

What if I want to charge a 12v car battery with a convertor so I can run my 12v stiff off of a different battery? Do I need to have a some kinda battery charging electronics between the convertor and the battery, or can I just hook the 12v side of the convertor straight to the battery?

 

[Truckoholic]

What if I want to charge a 12v car battery with a convertor so I can run my 12v stiff off of a different battery? Do I need to have a some kinda battery charging electronics between the convertor and the battery, or can I just hook the 12v side of the convertor straight to the battery?

A general rule around those voltages is that you need 2 volts higher in order to charge. Which is why 12 volt alternators put out 14 volts. I don't believe it will work very well to charger a 12 volt battery with 12 volts if it really is 12 volts. But if the converter puts out more like 13.8 volts, then it might work okay. Also, if you are mainly using the 12 volt battery kind of like a capacitor to store power for when your devices need a little more current, and the converter is going to be on most of the time as well providing the power to run the low current draw devices, then I would think that should work decently. But, I'm no pro at that stuff.

 

[plym49]

A clarification of the above - the charging voltage is set 15% higher. If you work backwards from the 14.2-14.4 volts that a 12 volt system is regulated at, you arrive at the nominal voltage of a 12 volt battery.

A battery is different than a capacitor. A capacitor stores electric charge on oppositely charged plates - it does not 'produce' electricity as a battery does.

 

[JasonS]

Do what you want, you have to pay to replace the batteries before their time. You CAN do it but it WILL shorten the life of your batteries, PERIOD! If the draw is really, really low, it might make little more than a few months or year difference. Bigger loads will kill your battery VERY quickly.

You have to look at this a little more carefully before stating that it will invariabley shorten the life of the battery. If your load is small enough that it does not cause the voltage on that battery to drop below 14V (or whatever is half your alternator's voltage) it will not affect the battery. All that matters is that the battery terminals see the ~14V and it will stay charged.

 

[tennmogger]

That's what I do in the Unimog U1300 and 404 Radio truck. Some converters can be connected directly to the battery but most can't. Two reasons: the current from the battery will flow backwards into the converter when the converter is off, and second, if there is a direct connection to a dead battery, a dead battery can cause a tremendous load on the converter when it is turned on. It may or may not be able to protect itself. I fried several Samlex converters until I 'learned'.

For the reverse flow current, the converter will most likely survive but the battery will be discharged. A diode in series, conducting toward the battery, will prevent reverse flow. A small resistance, even half to one Ohm, will prevent too high a load to a dead battery (12 v into 1 Ohm provides 12 amp flow limit). Size your resistor according to the converter rating (and include wire resistance)

Adding the diode compounds the need to turn up the converter voltage. Add another 0.6 volts for the diode junction drop.

I use Wilmore converters of a model that do not discharge the battery, and have good self protection for over-current. I float the 12v battery at 13.8 vdc (voltage recommended for most ham transceivers, and float v for many batteries) and that works great for normal usage, but I do connect a real charger to the 12v battery every few months to provide a cell-equalizing charge. (The truck batteries get an equalizing charge at the same time.)

Bob

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What if I want to charge a 12v car battery with a convertor so I can run my 12v stiff off of a different battery? Do I need to have a some kinda battery charging electronics between the convertor and the battery, or can I just hook the 12v side of the convertor straight to the battery?

 

[JasonS]

To put it in a little clearer terms. Your battery will have an open circuit voltage (ie. nothing connected to it) somewhere between 12.6 and 13.0V. If in use the voltage at the battery terminals is less than the open circuit voltage, current (and energy) is leaving the battery. Conversely, if the terminal voltage is above the open circuit voltage, current (and energy) is flowing into the battery. As long as the voltage at the battery approximates an appropriate float voltage (ie. 13.8 to 14V+) that battery will stay charged and won't even know that you have an accessory load connected. This is something that you can easily verify with a DMM but do it after your batteries have had time to settle with your accessory load.

 

[Jump Start]

Thanks everyone for the post great info

 

[ratat98]

Good info guys! Thanks for all the input! I also wanted to ask, can I ground the 12v side of the convertor to the same ground as the 24v system (frame) or do I need to have separate grounds for the 12v system? I think I know the answer to this, but I just want to make sure the gears in my head haven't lost any cogs...

 

[SoundGuy]

Depends on the converters. Most of them I have used have a common ground for the 24 and the 12 volts. In which case it is fine to do so. I would measure the voltage between the frame and the 12v neg to see what it is. If it is 0, it should be fine. If there is any voltage, I would put a 100? resistor to ground first and see if it goes to 0. If it does not go to 0 with a resistor, that mean there is current flow and connecting them would be a no no.

 

[DeuceDad]

Seafire, would say the Optima batteries are good replacement batteries for the two in the deuce? I need to replace mine and I am looking for cost efficient recommendations. Thanks.