What size converter charger should I get?

smkettner wrote:
and then let them sit disconnected on the concrete for a week.

Why do you mention concrete ?

We aren't doing to have that "concrete discharges batteries" discussion are we.....please not.

mrkoje wrote:
So then wouldn't 4 6vs in a series parallel suffer the same fate?

Yes very likely.
I suspect it would take longer and not be as pronounced but that is just a guess.

Sam Spade wrote:
If the two produce different voltages, they will be "fighting" each other.

There is no fight. The battery that has a higher resting voltage simply discharges to the level of the other and then they just sit peacefully.

Go ahead and equalize two identical batteries (that have been used in parallel) at the same time and then let them sit disconnected on the concrete for a week. Measure the resting voltages to quantify the difference. Post your results.

For the OP: 35 amp is fine for 1 to 4 batteries.

So then wouldn't 4 6vs in a series parallel suffer the same fate?

mrkoje wrote:

What I understand that you are saying is that by taking a 12v battery and connecting it in parallel with another 12v battery that because of differences in the two (even if they are the same battery model) will only produce approximately 1.5x capacity instead of 2x that would be expected?

I tried to explain it once. Let's try again.

Intitially you will get very close to 2X the capacity but as the batteries age, their relative capacity will change and the total will creep down.....because of what I stated before.
How long it takes for that to happen probably depends on luck more than anything.

I don't know of any better way to explain it. If the two produce different voltages, they will be "fighting" each other.

Matt_Colie wrote:

Sam Spade wrote:

mrkoje wrote:

Matt_Colie wrote:
Please do not parallel 12V jars. Even if they were side by side on the assembly line, by the end of the third week, they will not like playing in parallel. If you are lucky, you end up with capacity * 1.7. It will more likely be 1.5.

Please explain ...

Please search a bit.

Gross oversimplification summary:
If the two are not perfectly matched, part of the capacity of the stronger one will be expended trying to charge the weaker one. And when charging, the weaker one will sap off more of the charge.
And if one should fail completely, disaster can occur.

The disaster is rare and I think his 1.7 estimate is closer until they get really old but 6 Volts in series really are better.

Sam,
Thanks for picking this up before I got back here. Yes, that may be a gross oversimplification, but if we explained it in more detail many eyes would glaze over. There are so many important variables, that it is difficult to get arms around, but please believe us.

I have always loved a line from the original Stargate. Colonel Jack Anderson (Richard Anderson) was listening as the tech-savey lady explained how something worked. At the end, he looked at her and said,"That was a complete waste of a perfectly good explanation."

What I understand that you are saying is that by taking a 12v battery and connecting it in parallel with another 12v battery that because of differences in the two (even if they are the same battery model) will only produce approximately 1.5x capacity instead of 2x that would be expected?

Just for quick arguments sake - wouldn't it really depend at which rate you are using the batteries to determine how much usable capacity that would be usable?

Are you referring to a known scientific model here or an observed effect because of the low quality controls on typical 12v batteries say found at Walmart in which the rated capacities vs actual capacity could be substantially different from battery to battery?

I've tried researching a bit on what you are explaining and unfortunantley I have not come across anything that supports this claim yet. Im not saying I don't believe you at all. I just want to see the science of what you are saying.

Can you post a link to what you are referring to? My eyes don't glaze over when it comes to stuff like this.

Sam Spade wrote:

Matt_Colie wrote:
They said that you really can't charge a battery too hard if you do not over voltage the charge.

This is true but it's a funny way to state it.
It's kind of like stating that water will not overflow out of a bucket if you don't put too much IN it. ;)

Again, Thanks Sam,
The way I usually explain it is to say that charging batteries is like siphoning water.
If there is a lot of difference in levels, the flow can be fast.
When the container getting filled gets close to the source level, the flow will slow. If the containers safe level is the same as the source level, there can be no over fill.

I like your explanation better.

Matt

Sam Spade wrote:

mrkoje wrote:

Matt_Colie wrote:
Please do not parallel 12V jars. Even if they were side by side on the assembly line, by the end of the third week, they will not like playing in parallel. If you are lucky, you end up with capacity * 1.7. It will more likely be 1.5.

Please explain ...

Please search a bit.

Gross oversimplification summary:
If the two are not perfectly matched, part of the capacity of the stronger one will be expended trying to charge the weaker one. And when charging, the weaker one will sap off more of the charge.
And if one should fail completely, disaster can occur.

The disaster is rare and I think his 1.7 estimate is closer until they get really old but 6 Volts in series really are better.

Sam,
Thanks for picking this up before I got back here. Yes, that may be a gross oversimplification, but if we explained it in more detail many eyes would glaze over. There are so many important variables, that it is difficult to get arms around, but please believe us.

I have always loved a line from the original Stargate. Colonel Jack Anderson (Richard Anderson) was listening as the tech-savey lady explained how something worked. At the end, he looked at her and said,"That was a complete waste of a perfectly good explanation."

Well, if Xantrex knwos what they are talking about you'd need about 25 amps for your converter, but yes, a 35 will be just fine.. Since your battery is likely a MARINE/deep cycle, the slightly faster charge won't bother it much.. That is a starting battery after all, designed to move a lot of current (relative to total amp horus) not a DEEP CYCLE which needs a slightly slower charge.

mrkoje wrote:

Matt_Colie wrote:



Please do not parallel 12V jars. Even if they were side by side on the assembly line, by the end of the third week, they will not like playing in parallel. If you are lucky, you end up with capacity * 1.7. It will more likely be 1.5.

Please explain ...

Please search a bit.

Gross oversimplification summary:
If the two are not perfectly matched, part of the capacity of the stronger one will be expended trying to charge the weaker one. And when charging, the weaker one will sap off more of the charge.
And if one should fail completely, disaster can occur.

The disaster is rare and I think his 1.7 estimate is closer until they get really old but 6 Volts in series really are better.