Ammeter technical question
- Thread starter AOWYN
- Start date
noelex
Well-Known Member
Let me try to explain it better. If the house battery bank consists of battery of the same age and type both battery switches are left on and the house system is run with all batteries in parallel as if its one big bank.
The 2 banks can easily be separated for trouble shooting and periodic testing. A defective battery can be easily identified and isolated.
If a battery fails it can be substituted with local battery of different age and even chemistry.
It gives you a great deal of flexibility, particularly with options like lithium batteries becoming viable.
Yes connections can be where electrical systems fail, but 2 house banks gives you a redundant set of connections. Like a twin engine plane if one engine fails there is an instant backup.
pvb
Well-Known Member
On that basis, presumably you think it would be even more advantageous for each battery in the domestic bank to be separately switchable???
john_morris_uk
Well-Known Member
whoops - type in haste and repent at leisure: I was thinking it was a 7.5 kW and a lot and then promptly typed the wrong figure! You are absolutely correct. 13.8 Volts at 600 amps is actually 8280 watts - but these figures are slightly misleading as the battery won't be holding up 13.8 volts when you are drawing 600 amps and I don't believe that the bow thruster will be demanding 600 amps all the time.
noelex
Well-Known Member
To be able to disconnect and measure the resting voltage, or voltage after a load, of each battery would be nice.
The more the batteries can be easily individually isolated the easier troubleshooting becomes and the greater the redundancy. The ability to isolate individual battery and operate with batteries of different ages and chemistries is helpful. The extra connections enhance rather than diminish reliability.
Long distance cruising boats have to very self sufficient. Parts can take weeks to arrive. Batteries have an unpredictable life, can fail with little warning, and are heavy and hazardous making transport difficult.
The greatest gains come from separating the start and house banks as most boats do. 2 house banks prove greater security and I believe this is a superior system for boats that want greater reliability and independence. Further division suffers from the laws of diminishing returns, but I don’t see any great problems. Dividing the house bank further is fine by me
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pvb
Well-Known Member
So it's OK to have 2 separate house banks, so how do you use them and how big are they?
halcyon
Well-Known Member
Thinking out loud.
What if a Hall effect shunt was fitted to each battery terminal. the output then feeds a bar-graph for each battery.
Allowing all the batteries in the bank to be monitored and displayed at the same time. Then if a battery starts to fail, it will start taking more / less amps than the others, and the same for discharge.
Thus you do not have to disconnect and measure rested voltage.
Just a thought
Brian
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noelex
Well-Known Member
I did have 600AHrs in 2 banks 1x200AHrs and one 2X200Ahrs. These batteries were 12 years old and gradually, 3 batteries failed. As the boat now has a large solar array. 400AHrs was enough and Got 2 new 200AHrs batteries. These new batteries became one bank and I used the old 200 AHr battery which was still OK in the other bank.
Surprisingly the old battery went on for another 2 years. It died a few months ago so I now have 400AHrs in 2 banks 1X200 and 1x 200).
I think in a few years, when I cross the Atlantic I will get a new 1x200 AHr battery and keep the old and new batteries in separate banks.
The Batteries are Sonenscein batteries that have given me excellent service. In my previous boat they lasted 18 years and in my current boat they went for 12 and 14 years, but I think it would be foolish to cross the Atlantic relying on house batteries that were more than a few years old. I can manage on 200AHrs so one new battery is good insurance.
Despite the separate banks I use all the batteries to minimize the depth of discharge. When the batteries are the same age and type (as they are now) both battery switches are left on and they are connected in parallel, apart from periodic isolation to check they are both performing well, and all connections are sound.
Having 2 separate banks allows me to purchase a new battery and keep the old and new batteries separate.
When separated there is a slight loss of capacity due to Peukert's formula, but high loads like the watermaker are used when solar production is at its maximum so the discharge current when the battery banks are isolated is low in relation to the battery size, the effect is minimal.
I hope the above illustrates the versatility and advantages of 2 house banks. They can always be connected in parallel and operated as one bank. 2 banks just gives you options not available to a boat with a single house bank
Conachair
Guest
Another added advantage is to be able to have 1 bank disconnected from everything apart from solar to equalise. One day I'll get there. I think it would be worth splitting just so you get actually fully charge each bank every other day, I suspect very few cruising boats every get the batts back up to 100% charge.
noelex
Well-Known Member
Yes good point 2 house banks enables you to equalize when away from AC power (The last time I could plug into shore power was 2 years ago).
As you point out AGM batteries also like being charged to 100% occasionally, difficult to do when at anchor unless you can isolate the bank.
There are a lot of advantages and versatility gained for an extra battery switch, fuse holder and a few meters of battery cable. One house bank is fine if you plug into shore power often, and can buy good batteries and get them delivered the next day, but 2 house banks is worth the small cost for boats that have to be independent..
electrosys
Well-Known Member
If you're at all concerned about power loss in an ammeter (which is very small), then unless you're continuously monitoring the current - say with some kind of datalogger - then simply switch the ammeters out of circuit (by shorting them out) when you're not watching 'em.
There will still be some small losses in the cabling, but I guess you already knew that.
grumpy_o_g
Well-Known Member
How do you short out an ammeter
The shunt is pretty much a short anyway - it's just a calibrated bit of cable really. You'd be better off putting extra shunts in parallel if you want to reduce the voltage drop but I suspect most of that would come from the connections in practice anyway.electrosys
Well-Known Member
How do you short out an ammeter
Couldn't agree more that a shunt is pretty-much a calibrated 'short' - and I'm not saying that my advice is really worthwhile doing: for myself, I couldn't be arsed - the losses are so tiny ... but all I'm saying is that it could be done (to relieve the neurosis, if not the power loss) - but that there would still be some losses in whatever cable you used to do the 'shorting out' with. Indeed, the losses in all of the cabling in the installation will far outweigh that within the ammeter itself, so it's all pretty much a intellectual (well, ...) exercise anyway.