two batteries

[evilme28]

I’m a wiring novice. This is my first teardrop build. I’ve seen a number of wiring diagrams on here and feel pretty confident that I can run the lines as shown. I have some advisers that will be available when the time comes as well. I’m sure it’s a dumb question but is it anymore complicated to wire up two batteries than one. I'll have the batteries and charger / inverter in the tong box. The box is gonna be large enough to accommodate two batteries. Will I run the charger to both simultaneously? Do I just run both into the fuse panel and to the ground block or wire up one and switch to the other if it runs down? Are these dumb questions??? Don’t worry about hurting my feelings, I can take it


Also, does anyone have any suggestions for books on trailer 12v wiring, that I can study up on.

Tom

To little is bad, and to much is never enough, unless of course its just about right.

[cuyeda]

I will let one of our resident experts answer your wiring question. For basic trailer wiring, check out Joanne's flow chart to get get you started. Find it in one of the stickies up on top of this section, "My wiring plans"

[prohandyman]

Tom
What are you planning to run on 12 volt that you think you might need two batteries for? I think I have read on here a few times, and I can sure testify that I have been out for a least a 4 day trip on one deep cycle battery and have never ran it down. Now, I just run lights on my 12 volt, the coffee maker and microwave are 110. But I do leave the Galley lights on alot(12 volt), and have two small landscaping lights mounted on the side as courtesy lights under the doors That burn all night long.
Also, have you considered the weight you would have with two batteries?
Just MHO!

[Bristol Delica]

Hi

I would have to agree that a large capacity battery, fully charged, can last for days unless you are using equipment with a heavy amperage drew. If you are only using lighting and such like and you are not going to away from a charging facility for an extended period one battery should suffice especially if you are charging from your tow vehicle when driving.

HTH

IanJ

[evilme28]

Well I was thinking of putting in a toaster oven and dc heater for the cab. I just figured they would draw alot of juice. And if Im not somewhere I can plug in I would hate to blow all my juice on a hot pocket.

Ignoring me wont make me go away, I just get LOUDER.

[bobhenry]

http://www.nyc-arecs.org/Connecting_Batteries_and_Chargers_in_Series_and_Parallel.pdf

THERE YA GO ! ALL YA WANT TO KNOW !

[Dale M.]

Bottom line is if you want two batteries for "extra" capacity, you need to have two (or more) batteries wired in parallel, either battery to battery, or battery to buss bar (pos. to pos. - neg. to neg.).

Ideally the two batteries should be of same group number (amp hour capacity) and should be same (or close to ) same manufacture date. Basically start with two brand new batteries..... And yes you can use a single charger to charge batteries in parallel...

Lots of battery information here....

http://www.batteryfaq.org/


That was short answer........ It get more complicated as you read on...

You can use switches to isolate each battery during use... But there are some risks in switching from one battery to other under load, and also in charging batteries as one may not get charged if they are not both connected to charger at some point.... I'm in favor of keeping both batteries connected/charging at all times, just for simplicity of managing ""battery system"...

There are issues of if you use isolation switches and one battery is lower in charge capacity and you flip switches so strongest battery is connected to weaker battery (parallel) there will be a inrush of current to weaker battery and draining charged battery to point where batteries equalize....

IF you want to use two batteries and have them isolated, I would use two chargers, one for each battery to insure both are always charged and have a switch type system that only allows one battery at a time to be "connected" to TD "systems"....

Dale

[BPFox]

I would hate to blow all my juice on a hot pocket.

This officially qualifies as my "Post of the Week"!


I plan on running two batteries, but since mine will be 6V golf car batteries, I will be wiring them in series.

[Gerdo]

Keep in mind that the batteries must be the same kind/type/brand/lot number. In other words they must exactly the same. If not they will sit there and discharge each other untill they are both dead.

[rasp]

i run two 105 amp hour 12 volt batteries and a Xantrex 1500 all in parallel. the Xantrex 1500 has a 60 amp hour battery and a 1500 watt inverter. keeps the wifes cpap machine running for 4 nights. still had 75% charge left. though we did not run anything else. but i had no problems with the batteries.

Trojan batteries makes all kinds of deep cycle ones. some rv'ers like running two 180 amp hour 6 volt batteries in series, not sure why, instead of 12 volt ones.

[UK-Corlett]

You guys clack me up

Back to nature campers.
Just bring you microwave, air conn, TV, Hi Fi, flood lights, inverters etc.

People who live in hot climates across the world invent the siesta.
Hot Americans invent air-con.

Just kidding.
I know its very different for you in the US but here in little old Europe.
I did a 14 night tour of France on 2 x 7Ahr batteries.
Interior lights, charged my phone at night, little HiFi, etc.
Drained one and half drained the other.
For exterior flood light I use gas lanterns.

Seriously
My interior lights are 5v LEDs
My 12V battery drives a DCDC convertor to create the 5V
Even on a completely flat 12V lead acid (say 9V) you can still get enough current for interior lights.


Clive

Just the red box in this picture.

[Alphacarina]

If you were to connect two batteries in parallel, positive to positive and negative to negative, it's true that both would need to be identical - Same size, brand, age and so forth . . . . . but even then, it'a BAD IDEA. Many, many folks DO connect them in parallel and you'll find some uneducated (electrically) folks who will tell you that it doesn't matter, but it's still a bad idea . . . . . they just don't know any better, or they don't really care how long they last - Some folks have more money than common sense . . . . unfortunately, that's never been the situation in my case

No two batteries are ever electrically identical and connecting them together 24/7 will have them electrically trying to equalize each other - You'll have current flowing from one battery into the other. At 100% charged, it may be that #2 is ever so slightly weaker than #1, so current will flow one direction while at a partially discharged state it may flow the other direction. The end result is they will be forever wearing each other out and they won't last as long as they should and you won't get as many amp hours of usage from them as you would if you were using them separately. Using them one at a time allows you to 'measure' the approximate percentage of charge remaining in the battery you're not using with a simple voltmeter"



Note that this only works for a battery which is 'at rest' - As in not currently being used. You cannot make this measurement on the battery you currently have online if it is being used to power anything . . . . which is one more good reason you don't want your batteries connected together in permanent parallel

This is why the marine battery switch was invented. You can select which battery you want 'online' and discharge that battery only and when it's partially depleted, you can select the other battery. This also ensures that you'll be less likely to run out of juice all together, since when you run one stone dead, you'll know it and you'll know about how much you have left in the other battery, so you can conserve and not run out completely. The switch will have a 'BOTH' position where they ARE connected together in parallel and this position is used when you're charging them - That's the only time you should connect them together and you should swittch away from the 'BOTH' position as soon as you remove the charger

You can buy a marine battery switcvh for about $30 and I would certainly recommend one if you're going to use two batteries. With the switch, it doesn't matter if one battery is bigger than the other, or newer than the other, or another brand or another type - You'll have them disconnected from each other 100% of the time . . . . unless you're recharging, which is the only time it is recommended that you connect them directly together

Don

[rasp]

if you wish to take a look at electric golf carts or other electric transportation they run batteries in parallel, some use two six volters in series and several pairs of these in parallel. caterpillar uses two 12 volters in parallel and then another pair in series to get 24 volts.

where i work the emergency diesel fire pump is wired wire a series parallel combo of 12 volt batteries, if it were a bad idea then the insurance company would not allow it.

must be a lot of uneducated folks out there.

[Steve F]

if you wish to take a look at electric golf carts or other electric transportation they run batteries in parallel, some use two six volters in series and several pairs of these in parallel. caterpillar uses two 12 volters in parallel and then another pair in series to get 24 volts.

where i work the emergency diesel fire pump is wired wire a series parallel combo of 12 volt batteries, if it were a bad idea then the insurance company would not allow it.

must be a lot of uneducated folks out there.

A lot of these situations the batteries would be on a float charge the majority of the time, even the golf carts would go out for a round and then get plugged back in at the end of the day, their capacity would be greater than what could be expected to be used in a day. I don't think in any of these situations the batteries would get charged and then run close to flat and then charged again etc. And I bet the insurance company has a maximum life on the ones running the pump and they have to be replaced regardless at a set interval, certainly computer battery backup ones do.

Basically I think it comes down to maintenance, if the batteries are high capacity, sit on a float charge most of the time and are well looked after they should last a longtime regardless of how many are hooked together. If you have two batteries, drain flat, charge, drain flat, charge etc then one will drop off quicker than the other and have a detrimental effect on the other.

One thing I've always wondered about is what about batteries like the little 9V ones that are basically multiple batteries wired together (AAAA size inside I think) they come in rechargeable and last for ages, is this whole thing different with NICad and NiMH batteries etc?

Cheers
Steve

[Larwyn]

if you wish to take a look at electric golf carts or other electric transportation they run batteries in parallel, some use two six volters in series and several pairs of these in parallel. caterpillar uses two 12 volters in parallel and then another pair in series to get 24 volts.

where i work the emergency diesel fire pump is wired wire a series parallel combo of 12 volt batteries, if it were a bad idea then the insurance company would not allow it.

must be a lot of uneducated folks out there.

Rasp,

I agree with you 100% on this. I guess maybe those folks that were educated electrically, somehow came out "smarter" than those of us who decided to take our education mentally. Does that make us "mental"? I don't know. I do know that parallel batteries are in operation on many different types of equipment, most of it was engineered by electrical engineers who received their education in electrical matters from some of the best universities in the world over the years. I am curious how this is such a bad idea in a teardrop and why someone should consider himself so high and mighty as to call those who would parallel two batteries "uneducated".

I'm sure that there is some interaction between two batteries connected in parallel until they equalize, and I am sure there are some losses to this equalization process, perhaps even when under load. I'm also sure that even with these losses there is a real advantage to paralleling batteries. If you want the most possible use out of a battery I suppose using it individually isolated from the other would be the way to go. If you just want to go camping and use your lights, fan, whatever and not waste time worrying about your batteries, you can do that too. And if you have those two batteries in parallel you can bet that they will power your equipment much longer than one battery on it's own, though probably not by a factor of two. I find that quite acceptable and do not consider myself "uneducated" in electrical matters.

I guess it's just a matter of whether you want to go camping or on a battery care and maintenance exercise!.....