6 volt batterie conversion

[Lyons]

I would like to change my dying two house batteries to two 6volt batteries. Is there anything that I need to change for the electronics of the boat to work properly or can I just swap them in as long as they are connected properly. They are going into a R 27 tug

 

[knotflying]

Think about this. You have to hook up two 6 volt batteries in series to get 12 volts. You will not get double the amperage, only 12 volts and the amperage equal to one battery. Two 12 volts in parallel will give you 12 volts, but twice the amperage. If your single 6 volt has less amperage than double your 12 volts in parallel, then I would stay with the 12 volts.

 

[dante3756]

I differ somewhat with Lyons' response. I previously converted my two 12 volt house batteries to four 6 volt golf cart style batteries on a sail boat. There was approx. a 50% increase in total amps. Also, the golf cart batteries lasted much longer. Another plus is that they are easier to handle than a single super heavy 12 volt. Down side is that they are taller and clearance was a problem I had to solve. It seems you are aware that you must must connect two of the 6 volt batteries in series and then connect the pair of 6 volt batteries in parallel. I now have an R29 and will likely switch to 6 volt batteries when my existing batteries die, but only if there is sufficient room laterally and for clearance. Dante

 

[Levitation]

I have had a pair of 6 volt cart batteries (in series, natch) as an additional house set for 7 years
(in parallel with the house set with a Blue Seas isolation switch for testing and such)
The house set has been replaced once.
The cart batteries are still going strong.
ymmv sar bni :mrgreen:

 

[knotflying]

I just wanted to make it clear to Lyons that he was not necessarily getting more amperage by replacing two golf cart batteries for two deep cycle. He needs to compare what amp hours he is getting from 2 - 12 volt deep cycle batteries by adding the amp hours of each together against the amp hours he is getting from joining two 6 volt golf cart batteries together, which will only be equivalent to the amp hour ratings of one 6 volt battery. He may be getting better batteries that may last longer and that is it.
Also, sometimes we get hung up with "more is better". One needs to sit back and actually calculate what their usage will be while on the hook and also for how long. As many of you know I rely on the inexpensive flooded technology and replace my $86.00 each Walmart batteries every 3 years regardless of condition. I put a battery switch between the thruster and house and quite frankly I leave it on all the time. It gives me 1/3 more amp hours for house usage and 2/3 more power available when using my thrusters. I use my boat year round and top off the fluid every six months with distilled water. After a night on the hook my state of charge is at 80% and then either the solar panel kicks in or I am cranking up the engine and moving on and charging up along the way. The solar panel will usually not keep up with the refrigerator, but I am usually good for three days on the hook. So for me my setup with deep cycle works. For others that use more amp hours they may need to go the golf cart battery route, but may need four of them to accomplish the mission. Before moving forward do the math first to determine the requirement.

 

[Osprey]

Knotflying suggest we do the math, however my math is a bit different than his. Suppose we consider 12V, 100 AH batteries. Now with his setup he has two parallel house batteries providing a total of 200 AH plus a thruster battery providing 100 AH. He has installed a combining switch which, when on, connects the thruster battery to the house pair. So from a house point of view he now has 300 AH, 50% increase, not 1/3 ( 33%). For thruster application the increase goes from 100 AH to 300AH, a 300% increase not 2/3 (67%). I have the same set up and am pleased with the results.

 

[CAPTCRUNCH]

Maybe it's a typo in the post, but in our house an increase from 100 to 300 is a 200% increase, not 300%. Apologies if snarky and/or wrong.

 

[knotflying]

When I stated do the math, I was suggesting that one should add up all of the required amp hours for what they use on the boat while at anchor. The math may suggest that the need for additional amperage is not required.

With regard to the statements of adding the thruster. Perhaps the math is all about from what one is using as a starting point. Using the 12v 100 amp scenario, if I have 3 batteries equaling 100 amps (300 total) each, then the third battery gives me 33% more available amperage of the total. On the thruster side having only one 100 amp and adding 2 more (total 300 amps) gives me 66% more. By the way I also have 11 fingers. On one hand count each finger down - 10-9-8-7-6 plus the 5 fingers on my other hand gives me 11. :lol:

In any event the increase is significant for the cost of a switch and a couple of feet of battery cable versus buying new golf cart batteries that may not increase the amperage percentage as much as paralleling the thruster.

 

[Osprey]

Captcrunch, you are correct. Perhaps I should have written 3 times the AH. But it is all fun, we are not called Tug"NUTS" for nutin. Beyond that, total AH may not be all that relevant with respect to thruster operation. Should we really be looking at the change in available cranking amperes? That is, the ability to pump out current over a short period of operation.

 

[knotflying]

The real number that is important is RC, this is the Reserve Capacity. This is the number of minutes a fully charged battery at 80 ° F will discharge 25 amps until the battery drops below 10.5 volts. Also important is amp hour, (AH) is a rating usually found on deep cycle batteries. The standard rating is an Amp rating taken for 20 Hours. Unfortunately, you sometimes have to dig to get the information on different brands. Additionally, most of the "Deep Cycle" batteries sold off the shelf are really hybrid standard batteries and are not true deep cycle.
So full circle, 6 volt golf cart are true deep cycle. Do you need all that capacity based on what you are using and for how long? Based on your answer, perhaps just joining the thruster battery to the house is all you need.

 

[Lyons]

Sorry it took so long for me to get back to all of you
Thank you all for the help. It will give me something to work on over the winter

 

[JohnH]

I have never been completely satisfied with the arguments for putting 2 batteries in parallel. It seems to me that, unless they are EXACTLY equal and remain so throughout their lifetimes, the weaker one will inevitably drag down the stronger. This would mean that some of the capacity of the stronger goes to helping (i.e., charging) the weaker rather than doing useful work.

If, instead, these unequal batteries were connected in series, then both their output voltages would sum, and this voltage would diminish as the capacity of the weaker approaches its limit. If one battery were weaker, the total voltage might be less than the parallel arrangement, but there would be no capacity "wasted" by the stronger battery trying to charge the weaker.

For the series configuration, I worry a bit about the charging process. I assume that the 2 series batteries are charged together from a 12V charger. If the batteries are unequal in actual capacity, I don't know how the charging current would be distributed or if both batteries in a series configuration would be charged fully and properly. It would be better to separate them and charge each one from a 6V charger, but this is unlikely to be practical. Of course, a somewhat similar concern could be raised about combining 2 batteries in parallel and charging from a single source.

Comments?

-- John H

 

[snydzy]

In a series connection, what's important is that all the cells are similar in voltage, not capacity. All batteries, whether 6V or 12V are already a series of separate smaller cells.

 

[knotflying]

I have never been completely satisfied with the arguments for putting 2 batteries in parallel. It seems to me that, unless they are EXACTLY equal and remain so throughout their lifetimes, the weaker one will inevitably drag down the stronger. This would mean that some of the capacity of the stronger goes to helping (i.e., charging) the weaker rather than doing useful work.

If, instead, these unequal batteries were connected in series, then both their output voltages would sum, and this voltage would diminish as the capacity of the weaker approaches its limit. If one battery were weaker, the total voltage might be less than the parallel arrangement, but there would be no capacity "wasted" by the stronger battery trying to charge the weaker.

For the series configuration, I worry a bit about the charging process. I assume that the 2 series batteries are charged together from a 12V charger. If the batteries are unequal in actual capacity, I don't know how the charging current would be distributed or if both batteries in a series configuration would be charged fully and properly. It would be better to separate them and charge each one from a 6V charger, but this is unlikely to be practical. Of course, a somewhat similar concern could be raised about combining 2 batteries in parallel and charging from a single source.

Comments?

-- John H

Remember, series increases voltage and amperage stays the same. Parallel increases amperage and voltage stays the same. Just want to make sure you are not thinking of hooking up two 12 volt batteries in series.

 

[boaterjoe]

I completely agree with Dante that 4 six volt golf cart batteries will give you approx. 400 amp hours or 200 amp hours for use before recharging. This is much more than you would need each day on the hook. If you have the space this is the way to go. They are very forgiving and easy to maintain.
Joe
Cutwater 28