Safe to pull 12v from one battery of the four in M820?

[ben0192]

I need to power a 10 amp 12v fan and 3 amp 12v and currently wired it up to pull the current from one of the four 12v batteries. The vehicle is the normal 24v kind, so this seemed the easiest way to get 12v. But I didn't know if there was anything wrong with this setup, if perhaps this could cause some sort of weird imbalance issue related to charging or something. I'm hoping not as the current draw is relatively slight.

 

[Stalwart]

You can do it but you WILL BE shortening the life of your batteries, all of them. You said the key yourself, imbalance.

 

[caliber1]

You should install either a battery equalizer, or a 24VDC to 12VDC converter to power those loads. I currently have a converter wired up on mine, but plan to install an EQ.

There are 24 VDC fans out there, look at some bus shops. I know MCI and Van Hool both use 24VDC fans. Have a few at my shop.

 

[ben0192]

Thanks guys. Darn. I was afraid of that.

The person I bought it from has some cigarette lighter sockets he installed with 12v, they're wired to some small silver box with heat sink fins (I assume a 24 to 12 v converter). I was just afraid that I'd be drawing too much current. But in light of your answers I'll try to wire it to there instead.

 

[bearboley]

I have heard this discussed before. Yes your batteries life in theory will be shortened, but in the real world I doubt it will have much effect on longevity. I suppose a transformer 24-12 would be the proper way to do it, you could pull off all the batteries. My 5 ton had a 12v two way radio in it right from the military and they just pulled off of one battery.

 

[Truckoholic]

Yep this has been discussed quite a bit on here before. There are those who insist that the batteries will not charge evenly when hooked up that way. I just don't see it. I personally feel that if you are not drawing a huge amount of power from that one battery, that it should not be any kind of problem to worry about. But I've been bashed for that opinion before. I may not be an electrical genius, but I know a lot about how electricity and batteries work. But whatever. Apparently I am wrong and the entire civilian truck industry is wrong as well since just about every big rig out there has a 24 volt starter, yet the 12 volt accesories are drawn off of one of the batteries. But what the heck do they know?

 

[bearboley]

Yep this has been discussed quite a bit on here before. There are those who insist that the batteries will not charge evenly when hooked up that way. I just don't see it. I personally feel that if you are not drawing a huge amount of power from that one battery, that it should not be any kind of problem to worry about. But I've been bashed for that opinion before. I may not be an electrical genius, but I know a lot about how electricity and batteries work. But whatever. Apparently I am wrong and the entire civilian truck industry is wrong as well since just about every big rig out there has a 24 volt starter, yet the 12 volt accesories are drawn off of one of the batteries. But what the heck do they know?

I agree with you I don't think it would hurt a thing. But back in the early eighties and earlier big trucks did have 24v starters and operated everything else include the charging system on 12v by means of a seires/parallel switch. To support you todays trucks have 12v starters they run 3 batteries 2 of the same and a deep cycle to run the ecm and it has a constant draw on it. That sounds like a imbalance to me.

 

[turbovr6jetta]

Yep this has been discussed quite a bit on here before. There are those who insist that the batteries will not charge evenly when hooked up that way. I just don't see it. I personally feel that if you are not drawing a huge amount of power from that one battery, that it should not be any kind of problem to worry about. But I've been bashed for that opinion before. I may not be an electrical genius, but I know a lot about how electricity and batteries work. But whatever. Apparently I am wrong and the entire civilian truck industry is wrong as well since just about every big rig out there has a 24 volt starter, yet the 12 volt accesories are drawn off of one of the batteries. But what the heck do they know?

Ok, when you have 2 12v batterys that are being charged at 14.4v and you run them in series to get 24v for the starter the voltage of both batterys always stays the same. 2 12v batterys being charged at say 28v and pulling 12 volts off one of them causes one battery to be at a lower voltage. so say you have one battery at 14v and one at 12v making a total of 26v. the alternantor kicks in and charges till the voltage is 28v and it doesnt just charge the lower battery it charges both equaly so youll end up wth one at 13v and one at 15v making a total of 28. and the continual usage of one battery will eventually over charge one battery, thems the facts. However I dont know how to do the fancy science stuff to tell you how much of an impact a small amp draw would make but I know it would make one. Maybe not enough to ever really affect the life of your batterys but again I am no scientist.

I agree with you I don't think it would hurt a thing. But back in the early eighties and earlier big trucks did have 24v starters and operated everything else include the charging system on 12v by means of a seires/parallel switch. To support you todays trucks have 12v starters they run 3 batteries 2 of the same and a deep cycle to run the ecm and it has a constant draw on it. That sounds like a imbalance to me.

Again when working with all 12v batterys and charging systems it will all equalize at the same voltage. unless one isnt hooked up to the vehicles main 12v power. they sometimes do this so you have one battery that wont go dead if there is a power draw or such. it then can start your truck and charge the batterys back up. In this case the use a battery isolater and it still keeps the battery charged at thatever the alternators voltage regulator is set to. So no imbalance there

 

[DEVILDOC]

Thinking about adding 3 rd battery to my m35, Inside the cab in a safe box and wiring it up to the two batteries in series with the other 2 so it will still be 24v but extra CCA because xtra battery.
Then wire a fuse box from a donor car (junkyard). Then wire extra lights ect. Any thoughts

 

[bulldawg]

batterys

One of the Jeep owners probably know how to do it. We had to turn off our radios when cranking the jeep, if not the radios burned up.

 

[RedbeardTheZombieHunter]

I have a CB radio in my deuce that's hooked to the hot lead of the second battery (on the jumper from the negative on the first battery) so that the radio could be grounded to the inside of the cab. It works OK, but eventually I'd like to get a 24V to 12V voltage drop so as not to imbalance the batteries. I haven't had any issues with this arrangement yet (knock on wood) but I don't hardly use the CB except to listen to the NOWA weather broadcast once in a while.

 

[Speedwoble]

Just buy a converter or a battery equalizer, they are less than the price of a third battery.

 

[Stalwart]

To support you todays trucks have 12v starters they run 3 batteries 2 of the same and a deep cycle to run the ecm and it has a constant draw on it. That sounds like a imbalance to me.

Nope, you can parallel any size of battery of the same voltage rating and each will accept its own charge INDEPENDENTLY. It's when you put them in series is where the trouble starts. That is why you always replace batteries wired in series together in pairs. In a parallel configuration it isn't an issue unless you have a bad cell and that cell can pull down the new battery as well as its own.

I was going to mention the series parallel switches but you beat me to it.

As to someone mentioning a transformer, they only work in alternating current systems or in systems with pulsating DC. Perhaps you mean a convertor which is a MUCH more complicated device, but these days they are very affordable.

 

[quickfarms]

The idea of adding a 12 volt plug to charge a cell phone or iPod is not going to hurt anything due to the very low draw.

You want to draw 13 amps which is much larger of a draw and I would not draw that off of one battery.

 

[KsM715]

My 5 ton had a 12v two way radio in it right from the military and they just pulled off of one battery.

The military has access to a seemingly unlimited supply of batteries. The military did not do it per-say or there would be a TM/FM/TB for it. It was probably done at unit level.

One of the Jeep owners probably know how to do it. We had to turn off our radios when cranking the jeep, if not the radios burned up.

Thats because of all the strange voltages (and voltage drops) when cranking. The sensitive electronics in radios do not like that stuff.

 

[Recovry4x4]

I can only share my experiences with this. I bought an M35A2C out of Livonia TN and drove it back to Clermont FL. I ran a "run of the mill" 400 watt 120 inverter off the center tap and the only load on the inverter was my cell phone charger. By the time I got to FL I had a no start situation. Slaving the truck would start it but no matter how long it ran, it wouldn't restart. It wasn't until I pull both batteries and charged them independently that the issue was resolved. Sorry, I have no clue what the 400W inverter draws when charging a measly cell phone. That was my last attempt at center tapping.

 

[bearboley]

Stalwart is definitely up on his electrical and what he is saying makes sense after I though about it for a bit. I have learned some good info on this thread. Would like to say thanks.

 

[Recovry4x4]

A while back I bought a converter from Raul (scootertrs I think) in Miami. It was used and removed from some type of construction equipment. Not a huge amp version but adequate. Set me back just over $50 and works great. I'll post up the info on it when I return home.

 

[robert c neth]

i have a us navy dump truck and the heater and turn signals are wired from 1 battery only .had it 2 years so i dont know how long the batteries will last.

 

[Recovry4x4]

As promised, this is the converter I have. It's rated at 15A so it has more than enough juice to run small electronics.

ICT2412-15A