battery setup for alt delete. 2 6v or 2 12v

[Ryland]

I've jump started two cars in the last week off three of my 6v batteries in my electric car, 18v makes the starter spin kind of fast! you can also get 8v deep cycle batteries, but 8v and 16v chargers are harder to find.

DC/DC Converter Regulator 24V Step Down to 12V 20A 240W | eBay

Is one of the cheap DC to DC converters, mine is a Sure Power Industries converter that is designed for golf cart light kits.

[steffen707]

Originally Posted by Ryland

for my electric car I'm planing to hook my DC to DC converter up to a small motorcycle battery that I had to act as a buffer, that way I can push the limits of the size of the converter without having to worry about flipping on the wipers and defrost fan while driving at night, and when I do that my head lights will still be full brightness.

Do you mean that the defrost, wipers, fan and headlights would draw too much power from the dc/dc converter and so to not worry about the capacity, you'll just have the motorcycle battery to buffer the higher amp draw?

[Ryland]

Originally Posted by steffen707

Do you mean that the defrost, wipers, fan and headlights would draw too much power from the dc/dc converter and so to not worry about the capacity, you'll just have the motorcycle battery to buffer the higher amp draw?

Motors tend to draw higher amps when they start up, so while the wiper motor might only draw say 50 watts or around 4 amps while it's running (a guess) it might draw 4 times that for a fraction of a second when the motor first kicks on, so if you have your head lights and wipers on, then turn the deforst fan on, that deforst fan is going to have a high surge when it first turns on as well and there might be the freak timing where everything gets flipped on at the same time and a little 8 pound, 6amp hour motorcycle battery can handle a big surge, after all it's designed to handle a 200 amp load of the motorcycle starter for a few seconds, or you can keep your stock starting battery and use that as the buffer, and if you need to replace your starting battery soon think about getting a smaller/cheaper starting battery that is of course still sized large enough for your starter, it would making wiring all of this up a lot easier, then your higher voltage pack would be using the dc to dc converter to keep the starting battery up at 13.7v, just like the alternator did.

[mans]

If I use 3 of these 6v golf car batteries In series I would have 18v.
Each battery is 6v 220ah.

If i use this 3 battery setup with a 12v converter how many ah will the setup supply for me?

[brucepick]

Originally Posted by Ryland

...
DC/DC Converter Regulator 24V Step Down to 12V 20A 240W | eBay

Is one of the cheap DC to DC converters, mine is a Sure Power Industries converter that is designed for golf cart light kits.

I see it's rated at 12V output. Does it actually output approx 14V as we were discussing here?

[Ryland]

Originally Posted by brucepick

I see it's rated at 12V output. Does it actually output approx 14V as we were discussing here?

I can't find any specs on that one, but every other dc to dc converter that I've looked at the specs on is 13.5v or 13.7v, but then again that one is made in China and it's hard to say what it's real output is.
the Sure Power Converter that I bought, I bought because it was made in the US and had a larger heat sink on it, so hopefully it's well made, you do tend to get what you pay for, but not everyone wants to try an idea out with higher end parts.

[mans]

Originally Posted by mans

If I use 3 of these 6v golf car batteries In series I would have 18v.
Each battery is 6v 220ah.

If i use this 3 battery setup with a 12v converter how many ah will the setup supply for me?

guys i'm guessing this setup would provide 330ah and 12v . correct?

[Ryland]

Originally Posted by mans

guys i'm guessing this setup would provide 330ah and 12v . correct?

Yes... other then the DC to DC converter is only 90% efficient so 297 ah or 289ah if it's 13.7v... with lead acid batteries it's always better to have a larger pack size so it's shallower depth of discharge as 50% is as far as you want to go if you want them to last 5 years, if you drain down to 20% full then 2-3 years is about what you will get.

[ecomodded]

Originally Posted by 3dplane

Hey guys!
I read this thread and I feel I have to chime in because of my experience using parallel connections disagree with the RV article.

Key word in that article is "CHEAPER"
Quote:
"That is why the RV coach batteries have two marine 6 volt cells in series rather than cheaper 12 volt deep discharge in parallel. You get longer battery life with the two in series."

When you have two similar batteries parallel connected and they are being discharged,the article says that the one with lower internal impedance will give it's max current and basically die sooner than the other...
Let's think about this for a second.

What happens to a battery's voltage when you load it to make it produce large current flow? .... Correct! It's voltage drops or sags! Right?

Now how far can that voltage sag RELATIVE to it's buddy pair who is parallel connected to it? Not very far since they are "clamped" together so as soon as the stronger battery is trying to give it's all and it's voltage tries to sag,the other one with now slightly higher voltage will be forced to "help out" and equalize or even out the current flow.

If we look at the other example with two batteries that are also not exactly equal in regards to internal resistance and now they are connected in SERIES.

When we put an electrical load on this circuit, the batteries "see" or share or in other words have to produce the same current! The one with higher internal resistance will work harder /tries to get hotter than the other one.

How is that supposed to be better when over time they could get out of balance if not monitored?

I don't know but in reality using quality batteries that are pretty close match and are cared for,will not cause a problem.

I've got a couple of real world personal examples:

#1: I have a golf cart that I run on (big no no) car batteries! Not new car batteries but used/failed ones. All different age and size. Ranging from 55A/h to 74A/h.
I parallel connect two to make a pair,and then I series connect more of these pairs to get my desired system voltage.

After three years of use I only replaced the weakest pair because I was trying to set new personal speed records with it.

#2: Alternator disable switch in my car... first I added two 7A/h little sealed lead acid batteries parallel to the existing battery in my car! (no they did not explode).
Monitoring my system voltage showed improvement daytime driving but at night with the headlights on, voltage sagged close to 12.0V by the time I got home.

So I added another 55A/h car battery mounted in my trunk and now I can make my 58 mile round trip day or night without voltage sagging below 12.2V (under load of fuel pump,ignition,accessories etc.)

So I have a 55A/h ,60A/h, and two 7A/h batteries ALL parallel connected in my car for the past two months with no problems.

Sometimes a few hours after the trip home from work,the voltage recovers to 12.7V and I have to trick my automatic charger by turning on the headlights so it will start charging.

The key is to know your voltage in all situations , learn the limitations of the system so the batteries don't get abused.


Just my opinion.
Barna

Sorry for such a long Quote but lets leave it in context.

The problem with having two batteries of slightly different impedance's or plate condition is that one battery, the good battery which holds a full charge at 12.77 volts is always trying to feed the 12.62 weaker battery more voltage to even the voltage differences between the two. The weaker battery eats up the better/newer battery.

[steffen707]

I've been trying to read up on batteries this week, and I thought I read that normal lead acid batteries and golf cart batteries emit hydrogen and aren't rated for in cabin use. Is this true? Are you guys just ignoring the risks, or are you somehow running sealed compartment that vents to outside the car?