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View Full Version : 12v bat x2 = 24v @?? amps

coachgeo
03-31-2006, 12:13 AM
ok dumb question. I have a portable welder that runs off of two 12v batteries for most stuff. (12v for light stuff and aluminum)

1. do high dollar* 12v auto/truck etc. batteries have more amps than low dollar? (NOT Cold Crank Amps)

2. What about 12v lawn mower batteries, Less amps?
(NOT Cold Crank Amps)

3. Orrrr do they all have the same amps and the dollar figure is all about how long the amps/volts are available, how well they recharge etc.?

*(quality of construction/design)

Sandy
03-31-2006, 01:22 AM
12v bat x2 = 24v @?? amps

Yes and No. ;) If you want them to. Let's just say that with DC batteries, hooking them in series (pos to neg) will add the two voltages for 24 volts. hook them parallel (pos to pos) and the voltage remains the same. Series adds, Paralled divides is the rule.

All your questions add up to one question and that is "amp/hour" ratings. How many hours will this battery last at one amp vs another battery at one amp just for comparison purposes. Now that you have that in mind you can compare any two battery types, series or banks, whether it be at one amp for all batteries or at 375 cranking amps for all batteries to be compared. That factor is good for crude calculations or roughing out a decision to be made, then there are several other considerations that can be put into place.

But number one is that yes, the larger the battery in the auto/equipment world the longer the amp/hour rating for any reasonable range. What you call cheap may be due to some internal construction that just isn't important for grannies car as they are for a mud bogging 4x4, or do to local competition or maybe they are really overall cheaply built. Just too many things to really say one way or the other.

For your load considerations you need to think primarily about two things. For the common individual there are two basic batteries contructions that usually matter. One is a battery built for high and long cranking amps. Big engines, cold weather, hard to start engines, etc. These types are built for and do well in that range. They are made to put out some heavy cranking amps then be hit with the alternator/charger. They do NOT like to be deep cycled. Deep cycling is running one down to zip and charged back up. You'll get about ten to twelve of these out of even a new one. The other is a deep cycle (ha!) battery. Built to produce a very moderate amount of current for longer periods. RV appliances, trolling motors, inverter systems, welders----. These like to be charged less agressively.

Check into what is called RV or deep cycle batteries. Bigger is better naturally. Watch out tho. All of these will be slightly higher just because they are considered to be for hobby and pleasure and not necessarily a necessity. Watch out. In the boat and marine world there are many that are way overrated and over priced.

Don't mix and match deep cycle and cranking batteries in strings. Poor mating.

coachgeo
03-31-2006, 01:33 AM
Yes and No. ;) ...Thanx Sandy.

But... maybe I should have stated directly.. my question is which battery types will give the most amps for WELDING in a parallel 24v arrangement.

1. Do they all put out the same # of amps

2. Even Lawnmower 12v batteries?

I ask because I am getting poor penatration in my welds. This could be cause Im still shiatty at welding orrrrrr... cause my cheap lawnmower 12v batteries do not put out enough amps; or both. total welding time was only 15mins all added together so the batteries were not exhausted of juice yet. If its the Lawnmower batteries not putting out enough amps then I have to plan some new truck batteries into my budget.

George
Former Nor Cal- Siskiyou County resident

Sandy
03-31-2006, 01:51 AM
If you are connecting these batteries in parallel your are still at twelve volts but at a higher amp/hour capacity as well as a higher cranking capacity. If you are hooking them in series then you will have 24 volts, a longer amp/hour capacity and a moderately higher cranking capacity. However lawn mower batteries aren't much of a preference for what you are doing. Bang for the buck they are generally expensive compared to what you can get out of even the smaller car batteries. Even for lawn mowers they aren't worth a hoot. Chamber size is what the limiting factor is there. Any car battery would be a better choice.

No all batteries do not put out the same amps. That's what the basic series is trying to indicate and then there are some other internal factors but basically the series is a good key to watch for. The 24 series, 27 series, and so on. The series and physical size will dictate what kind of surges and overall output any given battery can do.

Am I doing okay here or going in the wrong direction??

BBchevy396
03-31-2006, 02:18 AM
A couple of 8D's, oughta do ya!!!

halbritt
03-31-2006, 02:55 AM
The maximum current that one can source from a lead-acid battery is dependent on construction. Deep cycle batteries generally have smaller plates with greater surface area. Starting batteries have larger plates for greater current carrying capacity and usually a lower internal resistance.

The amount of currrent in a circuit can be derived using ohm's law. The voltage will be 24 (for two batteries in series) and the resistance is going to be whatever the internal resistance of the battery is along with the leads and whatever. A battery with higher "cold-cranking amps" likely has a lower internal resistance. I also know that AGM batteries can source a lot of current quickly.

Pentawelder
04-03-2006, 07:01 PM
Another thought ... both batteries should be the same. Differences in state of charge and/or current capacity can cause the destruction of the 'lesser' battery in no time. Attempting to draw current through a discharged battery will force current through the discharged battery in the wrong direction.

coachgeo
04-03-2006, 11:16 PM
Thanx Penta and others. Right after this post I got offered to very new, but used price "matched" gel cell marine batteries. So I bought them and am using them.

rvannatta
04-04-2006, 10:57 AM
ok dumb question. I have a portable welder that runs off of two 12v batteries for most stuff. (12v for light stuff and aluminum)

1. do high dollar* 12v auto/truck etc. batteries have more amps than low dollar? (NOT Cold Crank Amps)

2. What about 12v lawn mower batteries, Less amps?
(NOT Cold Crank Amps)

3. Orrrr do they all have the same amps and the dollar figure is all about how long the amps/volts are available, how well they recharge etc.?

*(quality of construction/design)

the most reliable way to evalute the 'capacity' of a lead acid battery is to weigh the thing. Heavier batteries have more lead in them and will have more amps over time.

That said there are some other issues.

1) the 'jell' batteries seem to have more bang for the pound than the tradidtional 'water' batteries.' they are also more expensive.

2) Some batteries are designed to be 'deep cycle' batteries and some aren't.

The deep cycle batteries are ones that will provide a low amount of current over a long time and won't be damaged by exhausting them.

This is compared to the automotive battery that is optimized to provide a very high current flow for a short period of time (start the car) but is not intended dto be 'run down'.

The jell batterires seem particularly sensitive to 'deep cycling'---although there are deep cycle models. If you run a jell battery (identifiable by having round cases that hold a coil of lead plate instead of rectangular cases with flat plates) clear dead, it is not uncommon to have a problem to even get it to take a charge een t hough it is a fairly new battery.: :nono:

coachgeo
04-05-2006, 02:05 AM
Wow looks like I did good. The batteries I ended up with for 35 buks a piece is this one!
http://www.kingsolar.com/catalog/mfg/exide/pv27.html