Joining batteries to power mount

telecasterguru (Frank) · #1 13-05-2010, 12:56 PM

Not sure if this is the right spot for this but here goes.

I have an aversion to all things electrical e.g. I don't like getting zapped, but I want to run 2x 36Ah gell batteries together to power my mount and computer while at the SPSP this weekend.

Firstly, can it be done and secondly, if it can, how do I do it and would it be worth it (without getting zapped)?

Any ideas.

Thanks

Frank

Zaps · #2 13-05-2010, 01:41 PM

If they are 12V cells and your mount runs on 12V you will have to connect them in parallel: that is, positive to positive, and negative to negative. That will give you 12V @ 72Ah. (If you connected them in series - negative to positive - you'd get 24V @ 36Ah.)

Your local hobby or electrical supply store will stock the connectors and cables you'll need if you don't already have them.

telecasterguru (Frank) · #3 13-05-2010, 01:51 PM

Thanks Zaps.

Kal (Andrew) · #4 13-05-2010, 02:26 PM

1 battery for the mount, another one for the computer?

bojan · #5 13-05-2010, 02:36 PM

NEVER run batteries in parallel.
The problem is, if there is only a slight difference in voltage, one battery will discharge through another, which may cause overheating (due to large currents flowing between the two).

You simply run the whole thing one battery, and when it is empty, replace it with another one.

The similar goes for series connection, if batteries are not charged to exactly the same charge: when one battery is empty, there is a danger of reversing voltage polarity (because the other one will force current through empty one in opposite direction), this may destroy the battery pack.
However, this condition is easily detected (and avoided) because the overall voltage in this case drops below12 V

Marke (Mark) · #6 13-05-2010, 02:44 PM

Not exactly true , I have just been through this myself and asked similar question on here. I checked with battery supplier and manufacture both state its is perfectly safe to add then in parallel as long as they
are identical batteries. Charging is done as normal (use a good charger like C-tek) it will just take 2x as long to recharge.

Quote:

Originally Posted by bojan

NEVER run batteries in parallel.
The problem is, if there is only a slight difference in voltage, one battery will discharge through another, which may cause overheating.

You simply run the whole thing one battery, and when it is empty, replace it with another one.

mswhin63 (Malcolm) · #7 13-05-2010, 06:47 PM

I agree, I have installed many solar system in the past and to get the capacity we installed many in series and parallel. As long as the charging is done with 2 the batteries will equalise. I currently have 4 batteries in a series parallel arrangment and they are working fine.

bojan · #8 16-05-2010, 09:25 PM

Word of wisdom, guys ... don't do it.
Series is OK as long as one battery is not fully discharged.. But parallel is NO NO...
Not without adequate circuitry that will prevent the condition I am warning you about (even just a simple diode in series with each battery will do).

Zaps · #9 17-05-2010, 08:05 AM

Bojan, I respectfully disagree. If cells in good condition (new cells in particular) are connected in parallel, few or no problems should occur, especially if the cells are well-maintained and monitored.

Barrykgerdes · #10 17-05-2010, 08:20 AM

Bojan is right for most people if they are not familiar with the effects of unbalance in parallel connected batteries. With top quality deep cycle batteries it is the done thing to increase capacity but here the design of the batteries is intended to take care of this.

However many of the cheaper storage cells available these days do not age at the same rate. Thus after a few charges and discharges the unbalance will become enough to destroy both cells.

I have carried out tests using older units (identical outward appearance and same age) that have shown this to be the case. The first couple of charges gave double the battery charge life but after six charges the life was less than one battery and after the next charge both batteries were useless. Using other batteries from the same batch singly has allowed them to last through many charges. I have one particular old golf buggy battery that was no good in the buggy any more but has been in use for driving my LX200 in the field for six years.

Barry

bojan · #11 17-05-2010, 09:24 AM

Quote:

Originally Posted by Zaps

Bojan, I respectfully disagree. If cells in good condition (new cells in particular) are connected in parallel, few or no problems should occur, especially if the cells are well-maintained and monitored.

IF, IF, IF...

If you do it, it may cost you a lot at the end.
And, why it is such a big deal not to use batteries one after another, as they discharge? Especially because you may prevent the damage by not doing anything unusual actually (and I never said it will happen.. but it may...once is quite enough.. and why not avoid it?).

I am simply suggesting a good, safe practice.

Scorpius51 (John) · #12 17-05-2010, 10:40 AM

I agree with bojan. I would be using separate batteries for the mount and computer. Why tempt fate when there is a simple solution?