Multiple Batteries Evenly Charged

oxphatxo · Post by **oxphatxo** » Mon Aug 18, 2008 4:42 pm

Are you thinking about installing a battery bank into your project? This is a very important fact to know about how your batteries MUST be connected to properly charge each of them evenly and take advantage of greatly lowering your power resistance. (Which is a good thing).

First and most importantly, you need a proper charging system. Running a battery bank from your stock alternator will soon burn it out. The best way to charge a battery bank is to do so with a separate alternator designated just for that. The reason being, you will likely fry your vehicles cpu from all the voltage changes from the system draw if you only use one alternator. Keep your stock alternator for your vehicles own purposes, and perhaps to run 1 of your amps lets say for your highs.

Suppose you had 6 batteries. Each battery is rated at lets say 1000 amps with a resistance of 0.005 milli ohms at 12 volts to make it simple. You would of course need to connect all positives to eachother and all negatives to eachother. The trick to making the alternator think there is only 1 battery, 1 BIG battery, is all in the way you have this next step done. See the illustration below, or keep reading...

You will notice that all of the negatives are connected together and only on 1 side are they grounded to the chassis of the vehicle. The other end of the negative side of the batteries is given to your amplifier(s) directly. The same goes for the positive side. All the positives are connected together and then only 1 side of the positives of the batteries feeds the amplifiers and the other will be for your power cable ran to your second alternator.

You do not want to mix the front hood battery to any that are not identical. I also mean that the batteries must be all the same brand, model, and should also be at the same voltage within 2 decimal places. So no batteries that can only hold half a charge compared to your others that hold a full charge will do.

I mentioned in the beginning of this note that there would be a resistance change in all of this. For instance, your 6 batteries rated for 1000 amps each are now 6000 amps. Your resistance is also halved for each battery you have, so for six batteries you would divide to the power of 5. For example:

1st battery = 0.005 mohm
2nd battery divide by 2 = 0.0025
3rd battery divide by 2 = 0.00125
4th battery divide by 2 = 0.000625
5th battery divide by 2 = 0.0003125
6th battery divide by 2 = 0.00015625

That gives you 0.00015625 ohms resistance and 6000 amps worth of power. Which is MUCH less resistance than any stiffening capacitor in the world with MUCH more continuous amperage.

If there are any mistakes here feel free to correct me on anything as I just found out all this today when I met up with my alternator guy. I was bored today so I hope I helped someone out there...

KHPower · Post by **KHPower** » Mon Aug 18, 2008 5:18 pm

Whoa! Good info. I shall buy 6 Kinetics and get to wiring.

Now what are folks supposed to do that cant install a second alternator???

oxphatxo · Post by **oxphatxo** » Mon Aug 18, 2008 5:42 pm

If you must use your stock alternator, you should at least go and get it rebuilt to a higher amperage charging unit. Roughly $200-300. Sometimes for certain vehicles there are "regulator bypasses". They will allow your vehicle cpu to run without knowing what the voltage is at. I don't know too much about those, but I know you're lucky if you can find one to work with your year/make vehicle. Also you can get a different cpu that will work with the voltage changes. All this you would have to research yourself, but will still never be as good as a second alternator. A car requires usually 60-80 amps just to run its normal processes. The remainder would go to your battery bank and the harder you run an alternator, the hotter it gets and less effecient it will work. You will also notice your lights dim if you are drawing enough juice to your system. With a closed loop charging system you would never have that effect.

For reference, I am having my 93' Caravan taken in to get a custom bracket made to mount a second 225-250 amp alternator. They are also rebuilding my stock alternator with new parts. The mount is the expensive part, the new alternator and new belt is the cheap part. They are saying it will cost me roughly $1000 give or take. If they don't run into any issues.

All in all, if you run a couple batteries in your trunk, you would be better to remove your hood battery and just use the trunk batteries for the entire car and you will probably get away with your stock alternator for a while. But don't expect to maintain your maximum voltage all the time. Just remember to install the batteries the above method if using more than one identical power cell.

oxphatxo · Post by **oxphatxo** » Mon Aug 18, 2008 6:50 pm

You know what, scratch the whole charging method. I just found out something that I am gonna have to tell my alternator guy he is wrong about. I just realized and figured out, that there is no way possible of charging batteries in parallell without one of the batteries taking up all of the charge. Since no battery is ever exactly the same, the charge will go to the battery with the lowest resistance. The only TRUE method of charging multiple batteries is with a battery isolator.

I thought I would correct this before someone else looked at me like an idiot.

KHPower · Post by **KHPower** » Mon Aug 18, 2008 6:57 pm

Indeed more great info. i Have a van myself and have seen up to 4 alternators installed in similar. I think in some cases you can mount a second alternator where the factory air conditioning pump is located because it runs off of a serpantine belt( thats if the air conditioning unit doesn't work or would cost too much to fix.

What your are explaining above is for a daily driver right? Because I see this all the time in competition setups but you also see people charging the batteries up to par before comps and they do not use most for daily drivers.

In the example above with 6 batteries there is No battery isolator used correct? and all 6 batteries would run off of 1 of the two alternators?

nico boom · Post by **nico boom** » Mon Aug 18, 2008 9:48 pm

Every battery should be electrically insulated from the other, by means of a diode-block for sure.
We used a diode block with compensating-diode, which allows the alternator to "sense" the voltage of the battery's and charge them with 14.4 volts, no matter what the conditions are.
The compensating-diode COMPENSATES for the voltage drop [mostly around 1-1.3 volts] over the main diode that devides the power between the batteries.
If you connect several batteries together like in your first example, the "worst" battery would drain the better ones, and like you said, it would drain all the power while charging.
It is also a good idea to mount a simple temp feeler on your alternator to monitor the temperature while charging; HIGH OUTPUT alternators DIE EASILY from overheating!!
There is a lot of info about this subject everywhere; good thing that you checked your first story yourself, trying to help others.

I myself used to go around asking a lot of questions at the local shop where they repair alternators and stuff; later on they had me disassemble one, and telling them how it worked.."to find out if I'd been listening to them" haha!
GOOD LUCK, and if multiple batteries are not an option for you; go for a HELIX POWERSTATION.
http://phoenixphorum.com/helix-xxl-powe ... t6456.html
Nico

oxphatxo · Post by **oxphatxo** » Wed Aug 20, 2008 4:46 pm

Nico, have you heard of any other "power stations" before? Other than Helix's? The Helix type looks nice and everything, but isn't there anything bigger than that? I think I read that you would need to supply your stereo amperage demands with one of them, so what happens if you're running over 11000 continuous watts? They expect you to buy 8 or 9 of these things? That is if you had 1 per 100 amps it looks like...

nico boom · Post by **nico boom** » Wed Aug 20, 2008 10:12 pm

No, as far as I know this is the only really working device there is on the market, and yes, they deliver 100 amps cont, and 200 peak.
BRAX had a device also called powerstation, but that was only a fancy stiffening cap, that was not crancking up the voltage like the HELIX does.
Powering so much amps demand for multiple powerstations linked together.....multiple batteries is far better [CHEAPER] in that case IMO.
You only need to have the space for them, in both cases you will need a BIG ALTERNATOR!

oxphatxo · Post by **oxphatxo** » Sat Aug 23, 2008 6:09 am

Check the install section, my setup with pics is in there now.

nico boom · Post by **nico boom** » Sat Aug 23, 2008 6:20 am

Checked!