Domestic Batteries in Parallel

[RichardS]

Was it skipperstu who had an awkward battery failure experience earlier this year?
That could have been a serious nuisance had he just started the ARC or been in an obscure corner of nowhere.

If you want to design your system to be more resilient and avoid that kind of trouble, it's worth considering different configurations.
There can be other benefits too. We once added an extra sub-bank just to run the fridge. Doing it this way meant:
+ We didn't have to buy all new batteries
+ The fridge could not run down the main house bank
+ we could minimise wiring by having the fridge bank nearer the fridge.
+ we could fuse the two banks separately
+ when the older batteries began to lose performance, it was easy to diagnose.
+ no single point of failure exists which could leave the boat with no house power.
+ it avoided the issue of not really having space to have all the batteries together anyway.
+ no worries about the different banks being at different temperatures and not sharing charge.

- limited capacity to run the fridge for days on end. We bought some ice with the savings.

Depending on what your electrical needs are, it might be worth considering, but fair enough, it's not for everyone.

But aren't those advantages considerably offset by the cost/complications of the additional charging balance circuits and isolation switching?

Richard

 

[GrahamM376]

If you want to design your system to be more resilient and avoid that kind of trouble, it's worth considering different configurations.

I have 2 12v banks (each is 2 x 6v Trojans in series) Normally, the 2 banks are paralleled but if there's a problem I can switch to separate and use either one independently. Also have separate engine battery but can start from domestics if that has a problem.

 

[lw395]

But aren't those advantages considerably offset by the cost/complications of the additional charging balance circuits and isolation switching?

Richard

Not significantly.
There are many affordable solutions.
Dual output chargers, B to B chargers, splitters off solar panels, VSRs etc many of which don't add much real cost.

Fair comment though, it's best to think about the system as a whole.

Starting with analysing what you want and need.
I can remember setting off for a week with just a car battery and no means of charging it!

 

[skipmac]

Here's my thoughts on these points.

Was it skipperstu who had an awkward battery failure experience earlier this year?
That could have been a serious nuisance had he just started the ARC or been in an obscure corner of nowhere.

Again, if it is a failure of one battery in a large bank it's quite easy to remove that one (or pair in the case of 6V) by removing a couple of connecting cables.

If you want to design your system to be more resilient and avoid that kind of trouble, it's worth considering different configurations.
There can be other benefits too. We once added an extra sub-bank just to run the fridge. Doing it this way meant:
+ We didn't have to buy all new batteries

Why would you have to buy all new batteries? If the existing batteries are in bad condition then would time to replace them anyway. If the existing batteries are good then putting one (or one pair) of new batteries in the bank won't cause the boat to explode or kill either the older or new batteries.

+ The fridge could not run down the main house bank

One large main bank will run the fridge longer with less likelihood of running down. If powering the fridge by it's own bank one shouldn't run that down either if the plan is to maintain the health of the batteries.

+ we could minimise wiring by having the fridge bank nearer the fridge.

But wiring to a fridge is done quite well with a moderate size wire, 8-10 gauge is fine depending on the distance but wiring a separate bank to allow for high charging currents, etc requires large size cables.

+ we could fuse the two banks separately

It's quite easy to fuse individual batteries in one bank if that is a concern. For me I see no problem in one fuse for the entire bank.

+ when the older batteries began to lose performance, it was easy to diagnose.

I guess this might be a slight advantage but it's not that difficult to test individual batteries in a bank.

+ no single point of failure exists which could leave the boat with no house power.

Well if the fridge bank is wired with automatic isolators to maintain charge but prevent discharge into the house bank and vice versa at the cost of quite a bit of complexity in wiring and systems. The same can be done with significant other advantages by having an isolated starting bank. This setup, if one does for some reason lose all charge in the house bank it's quite easy to crank the engine and charge back up.

+ it avoided the issue of not really having space to have all the batteries together anyway.

This is a point but it's also just as easy to make physically separated batteries part of one bank.

+ no worries about the different banks being at different temperatures and not sharing charge.

Not sure I understand this point. Do you have a charging system that sends different voltages to different banks?

- limited capacity to run the fridge for days on end. We bought some ice with the savings.

With a solar panel and single bank I can run my fridge forever and still keep the batteries full.
On passage once I add autopilot will have to do a little more.

Depending on what your electrical needs are, it might be worth considering, but fair enough, it's not for everyone.