Adding a 12volt battery

[kab69440]

No matter where you tap that 12v, all the batteries in that circuit are being subjected to excessive charging current.

I bought a 12v accessory plug at a local department store for $10. It took a step drill and five minutes to install it. That's what I use to charge my 12v. If I was so desperate for a little extra 12 v, I'd just remove the lead for my winch( I use the contactor leads to get the 12 v under the dash and tap my fuse block for the other accessories from that) and tap the main pack with it temporarily. I can't see that happening, though. I've put in a lot of 16 hour days on that cart and never run out of 12 v.

[JohnnieB]

Originally Posted by Hemicj

I am trying to reason this out.
1. If a lawn mower 12v battery was wired into the last two 6volts why would that overcharge and boil those last two 6v batteries.

2. The charger charges until the intire pack is up.

3. A battery will only hold so much of a charge and the charge will move on to the next in line.

4. So if that was the case wouldnt the first and second battries in your pack always get overcharged. Just asking..

1. The two 6V batteries that the 12V battery was wired in parallel with, would more likely be undercharged. On the other hand, lawn mower batteries are SLI type batteries and are typically in the 10-20AH range, so if its terminal voltage was less then the pair a 6V batteries it is in parallel with, which is likely, it is going to receive the majority of the charging current designed for 225AH batteries, or will be hit with about 10 to 20 times its normal charging current. If you are luck, that will only kill the lawn mower battery, if you are unlucky, it will explode it.

2. No, not exactly. The charger pumps current through the series string until the combined voltage of the series string totals about 45V. The charger only senses total voltage, so if one or more of the batteries has abnormally low on-charge terminal voltage, the rest are charged to an abnormally high voltage; And the opposite is true if one or more of the batteries has an abnormally high on-charge voltage.

3. That isn't how batteries in series charge. They all have the same current passing through them, so they all charge simultaneously rather than sequentially. If the battery pack is imbalanced, (IE: some batteries used more than others or connected in something other than a pure series string), they will not be charge equally.

This is why a new battery quickly deteriorates when added to a used pack and a relatively new battery pack quickly goes bad if a failed new battery is replaced with an old battery.

4. No, that isn't the case. See #3

[rhinomike]

I use a 12 volt battery for my lights and accesories. I use a lawn mower battery. I installed an onboard charge I got at Harbor Freight for 20 bucks. I leave an extension cord at my charger and plug it in once a week or so..... Works great. The battery lasted 3 years before i had to get a new on a few days ago. You can see a little bit of it in this pic...

[madoc1]

wow! that shop is too clean.

[rhinomike]

Originally Posted by madoc1

wow! that shop is too clean.

I wasnt even done with my shop yet.... It got better. LOL. Sorry to jack your thread but I love showing off my shop... LOL.

[chloe]

Ok, I am now sufficiently jealous

[cloead]

I just use a separate charger to keep my onboard 12v battery topped off. I use it to power my head/tail lights and radio.

[cloead]

And also extremely jealous of your shop. My 2 car garage is a wreck.

[Hemicj]

Originally Posted by JohnnieB

1. The two 6V batteries that the 12V battery was wired in parallel with, would more likely be undercharged. On the other hand, lawn mower batteries are SLI type batteries and are typically in the 10-20AH range, so if its terminal voltage was less then the pair a 6V batteries it is in parallel with, which is likely, it is going to receive the majority of the charging current designed for 225AH batteries, or will be hit with about 10 to 20 times its normal charging current. If you are luck, that will only kill the lawn mower battery, if you are unlucky, it will explode it.

2. No, not exactly. The charger pumps current through the series string until the combined voltage of the series string totals about 45V. The charger only senses total voltage, so if one or more of the batteries has abnormally low on-charge terminal voltage, the rest are charged to an abnormally high voltage; And the opposite is true if one or more of the batteries has an abnormally high on-charge voltage.

3. That isn't how batteries in series charge. They all have the same current passing through them, so they all charge simultaneously rather than sequentially. If the battery pack is imbalanced, (IE: some batteries used more than others or connected in something other than a pure series string), they will not be charge equally.

This is why a new battery quickly deteriorates when added to a used pack and a relatively new battery pack quickly goes bad if a failed new battery is replaced with an old battery.

4. No, that isn't the case. See #3

Thanks for the info, very informative. I think I will start out not looping the 12volt into my battery pack and see how long it will stay up. I will get back to this post when I have came to a conclusion. Thanks again to all that posted...