Batteries on opposite sides of boat?

[oldmanofthehills]

Connecting batteries in parallel – BatteryGuy.com Knowledge Base

That article says more about the problems that can occur if the batteries are not of the same age or type, or you get unlucky and one of the batteries starts to degrade or even fail before the other. One check you can do is to check the voltage of each battery to make sure that they match, that will show if one is starting to degrade. As I said before the risks of connection two batteries of the same type and purchased at the same time are minimal, but even if you connection a battery of the same type to an older one, it's asking for trouble in terms of how the pair perform.

The consequences of failure of a parallel bank are fairly trivial for an aux supply system, particularly if it is done Westerly standard as 1 - 2 switchable, but even if not it is the work of a few moments to transfer load via jump lead to a dedicated engine start battery.

The irritation of aux batteries going flat due to our 21st century usage is ongoing. The annoyance of rebuilding boat to accomadate a bigger single battery or wrecking ones back lifting one in, are both high prices to pay.

There is the ideal blank sheet of paper solution, but as an engineer I would always seek the most practical or lowest footprint one

 

[PaulRainbow]

Batteries in series need to be matched, but if in parallel and not equally charged then the one that's more charged will attempt to have a higher voltage, and so will supply more current to the load, or even charge the less charged battery, so the pair will keep themselves in balance.
Similarly if one gets to be fully charged before the other then the one that still needs charging will draw more current from the charging source until it too is fully charged.
However, one battery could kill the other if it it develops a short circuit cell

If connected correctly the batteries will all be balanced.

If you have a bank of four batteries and one fails it can be disconnected and the failed battery could be replaced. If you have a single, giant, battery and a cell fails you lose all battery power and need to replace the whole thing.

 

[PaulRainbow]

I’m looking to add another house battery to the existing one and engine start battery on my Westerly Berwick. I’d prefer not to have all the weight on one side. Is it OK to have one house battery on each side connected in parallel, or would I be better off with house batteries on one side in parallel and engine start on the other????

Just to clarify, in these muddy waters, my advice would be to fit the two domestic batteries together. Connect them in parallel and connect the negative to one battery and the positive to the other, job done.

If the engine battery still fits in the battery space, i'd leave it where it is. On a Berwick the engine battery doesn't need to be huge and heavy and the small amount of weight will not make a noticeable difference to your boat. To put it in some kind of context, a 14 stone person will weigh more than all 3 batteries put together, what if two people sit on one side of the boat ?

 

[TNLI]

It does not quite work like that as the bigger battery has the same number of cells as the smaller one. In reality it's the connections from the cells to the posts that sometimes fail. A partial failure of one battery will pull the whole lot down to the same voltage. If you are going to fit more than 2 matched batteries in parallel the easiest thing to do is to fit another battery selector for the house batteries. You can also fit heavy duty diodes, but that would probably be more expensive, and having a selector often proves useful in terms of the extra control it gives you over how your battery bank is used.

 

[PaulRainbow]

It does not quite work like that as the bigger battery has the same number of cells as the smaller one. In reality it's the connections from the cells to the posts that sometimes fail. A partial failure of one battery will pull the whole lot down to the same voltage. If you are going to fit more than 2 matched batteries in parallel the easiest thing to do is to fit another battery selector for the house batteries. You can also fit heavy duty diodes, but that would probably be more expensive, and having a selector often proves useful in terms of the extra control it gives you over how your battery bank is used.

All 12v batteries have the same number of cells, what's that got to do with anything ?

You can have a small stater battery in parallel with a pair of 250ah domestic batteries, so what ? So long as they are the same voltage it doesn't matter.

If you had 4 batteries in parallel and one battery failed because the internal connection to the post failed you would lose that battery. All that would happen is your capacity would be lower. If, as you suggested, a single battery was fitted and the internal connection to the post failed you would lose all power and would have to replace the whole battery, rather than 25% of your batteries.

These is no good reason not to have multiple batteries connected in parallel, provided they are correctly connected.

 

[jwfrary]

You said:

"It's better practice to simply fit a bigger battery. If you have no alternative then add a house battery selector switch and diodes to any battery chargers to allow both to be charged evenly at the same time. "

That is what is nonsense. No idea where you got that idea from, there is no mention of that in the article you linked to.

Banks of batteries, correctly connected in parallel and correctly connected to the boat work perfectly well and have been doing so since batteries were invented.

I agree with paul here, big batteries are a pain, much more than a 140 ah agm is just unmanageable for normal people.

Correctly wired with sufficient cross section theres no reason why it shouldn't equal its contemporary with a significant reduction in risk of s hernia.

Added to that if and when you do get a failure it can be disconnected and you can still get home, where as a big battery is pretty much eggs in the one basket.

 

[TNLI]

All 12v batteries have the same number of cells, what's that got to do with anything ?

You can have a small stater battery in parallel with a pair of 250ah domestic batteries, so what ? So long as they are the same voltage it doesn't matter.

If you had 4 batteries in parallel and one battery failed because the internal connection to the post failed you would lose that battery. All that would happen is your capacity would be lower. If, as you suggested, a single battery was fitted and the internal connection to the post failed you would lose all power and would have to replace the whole battery, rather than 25% of your batteries.

These is no good reason not to have multiple batteries connected in parallel, provided they are correctly connected.

The first part of my reply was just because a previous poster said larger batteries have more cells.
When a battery fails it's rare for it to fail completely to an open circuit, so it will often have an adverse effect on the entire battery bank. Mixing battery types is asking for trouble as they will not charge up at the same rate due to differences in their internal resistance. It's definitely a bad idea.
It would be good if you read the last 2 links I posted that point out some of the risks involved in wiring a batteries in parallel.

You also need to think about how a parallel bank is charged as this article covers if you have more than 2 batteries involved:
How to Charge Lead Acid Marine and RV Batteries in Parallel | Impact Battery

Try reading this one again, as mixing batteries is not good news:

Connecting batteries in parallel – BatteryGuy.com Knowledge Base

 

[PaulRainbow]

The first part of my reply was just because a previous poster said larger batteries have more cells.
When a battery fails it's rare for it to fail completely to an open circuit, so it will often have an adverse effect on the entire battery bank. Mixing battery types is asking for trouble as they will not charge up at the same rate due to differences in their internal resistance. It's definitely a bad idea.

You are the one that said "In reality it's the connections from the cells to the posts that sometimes fail. ", although that's not even true.

No matter what the cause of failure, if you only have one battery and it fails you are screwed. If you have a bank of multiple batteries and one fails you can isolate the failed battery and continue to use the others.

No one has said anything about mixing battery types.

It would be good if you read the last 2 links I posted that point out some of the risks involved in wiring a batteries in parallel.

As someone who designs and installs electrical systems on boats for a living, i'm well aware of how to connect batteries, thanks. Just because you read (misread) a couple of web articles doesn't make you an expert on the subject, much of what you have posted in this thread has been incorrect/ill informed.

 

[TNLI]

You are the one that said "In reality it's the connections from the cells to the posts that sometimes fail. ", although that's not even true.

No matter what the cause of failure, if you only have one battery and it fails you are screwed. If you have a bank of multiple batteries and one fails you can isolate the failed battery and continue to use the others.

No one has said anything about mixing battery types.



As someone who designs and installs electrical systems on boats for a living, i'm well aware of how to connect batteries, thanks. Just because you read (misread) a couple of web articles doesn't make you an expert on the subject, much of what you have posted in this thread has been incorrect/ill informed.

 

[TNLI]

Sorry for giving the impression that post to cell fails are common, as I've only had them on new cheap Chinese car batteries. I am not saying you should not add batteries, it's just better not to add too many in parallel without using a selector or diodes to prevent one battery causing the entire bank to go flat, or to fail to charge up in an even manner. It is important to occasionally check the voltage of each battery to see if one is causing an issue.

I would advise anyone that has technical questions to be careful about asking in a forum, as you can easily get wrong opinions from so called professionals and experts. The best thing is to use a good search engine to find associated technical opinions, which is why I reply with links rather than opinions.

Another article relating to charging multiple batteries:
Charging two battery banks - Practical Boat Owner (pbo.co.uk)

 

[PaulRainbow]

Sorry for giving the impression that post to cell fails are common, as I've only had them on new cheap Chinese car batteries. I am not saying you should not add batteries, it's just better not to add too many in parallel without using a selector or diodes to prevent one battery causing the entire bank to go flat, or to fail to charge up in an even manner. It is important to occasionally check the voltage of each battery to see if one is causing an issue.

I've tried to be as polite as possible when correcting your errors and silly claims, but you just don't know when to give up. You make a claim, then retract it when challenged and make a new one.

What sort of diodes would you fit between parallel batteries, bearing in mind that the domestic bank could be used for emergency engine staring ? How will you overcome the voltage drop caused by the diodes ?
How will you check the individual battery voltages ?

I would advise anyone that has technical questions to be careful about asking in a forum, as you can easily get wrong opinions from so called professionals and experts. The best thing is to use a good search engine to find associated technical opinions, which is why I reply with links rather than opinions.

This IS an internet forum. I'm not giving an opinion, i'm stating facts. I've been working with DC systems for close to 50 years, i might have picked a thing or two up. You might do well to listen.

Another article relating to charging multiple batteries:
Charging two battery banks - Practical Boat Owner (pbo.co.uk)

That article has nothing to do with connecting batteries in parallel, it is about charging more than one battery/bank. The two batteries in the picture are not even wired in parallel.

 

[Alex_Blackwood]

I would advise anyone that has technical questions to be careful about asking in a forum, as you can easily get wrong opinions from so called professionals and experts. The best thing is to use a good search engine to find associated technical opinions, which is why I reply with links rather than opinions.

 

[TNLI]

I've tried to be as polite as possible when correcting your errors and silly claims, but you just don't know when to give up. You make a claim, then retract it when challenged and make a new one.

What sort of diodes would you fit between parallel batteries, bearing in mind that the domestic bank could be used for emergency engine staring ? How will you overcome the voltage drop caused by the diodes ?
How will you check the individual battery voltages ?



This IS an internet forum. I'm not giving an opinion, i'm stating facts. I've been working with DC systems for close to 50 years, i might have picked a thing or two up. You might do well to listen.



That article has nothing to do with connecting batteries in parallel, it is about charging more than one battery/bank. The two batteries in the picture are not even wired in parallel.

You can buy heavy duty diodes for each battery, although did I say in a previous post that they are expensive, although have an extra advantage of acting as a rather crude heavy duty fuse, as they melt if you suffer a dead short. I also stated that it's better to fit an additional battery selector to provide a more reliable set of house batteries.
The voltage drop from expensive heavy duty diodes is not very significant in engine start terms, although I would bear in mind that the voltmeter and charger connections do need to go directly to the batteries, so using diodes does complicate things.
The Practical Boat Owner article link was a tad off topic, but useful if you are wiring up a new bank of batteries.

From the point of view of a reliable battery system, it is worth thinking about the regulations for modern lifeboats that I follow. Those regulations say that if an engine can't be hand started, you need 2 start batteries. House batteries are not a great alternative as many boaters have a habit of running them down too low to start their engine. I'm very keen on reliable systems, which is why I have 2 main battery selectors for a total of 4 batteries, (2 house and 2 start), although I've nothing against wiring two batteries of the same type and age in parallel. The problems in reliability or efficiency terms seem to start with more than 2, when I would recommend either buying bigger batteries or using a selector.

One word of warning about very cheap house batteries, and the ones advertised as for use in caravans in particular, is that they can suffer post to plate failures like cheap car batteries, but in reality are a not deep cycle at all, so they don't last long. They are also useless for starting anything.

 

[PaulRainbow]

You can buy heavy duty diodes for each battery, although did I say in a previous post that they are expensive, although have an extra advantage of acting as a rather crude heavy duty fuse, as they melt if you suffer a dead short. I also stated that it's better to fit an additional battery selector to provide a more reliable set of house batteries.
The voltage drop from expensive heavy duty diodes is not very significant in engine start terms, although I would bear in mind that the voltmeter and charger connections do need to go directly to the batteries, so using diodes does complicate things.
The Practical Boat Owner article link was a tad off topic, but useful if you are wiring up a new bank of batteries.

From the point of view of a reliable battery system, it is worth thinking about the regulations for modern lifeboats that I follow. Those regulations say that if an engine can't be hand started, you need 2 start batteries. House batteries are not a great alternative as many boaters have a habit of running them down too low to start their engine. I'm very keen on reliable systems, which is why I have 2 main battery selectors for a total of 4 batteries, (2 house and 2 start), although I've nothing against wiring two batteries of the same type and age in parallel. The problems in reliability or efficiency terms seem to start with more than 2, when I would recommend either buying bigger batteries or using a selector.

One word of warning about very cheap house batteries, and the ones advertised as for use in caravans in particular, is that they can suffer post to plate failures like cheap car batteries, but in reality are a not deep cycle at all, so they don't last long. They are also useless for starting anything.

Can you post a schematic showing where you would fit diodes on a four battery domestic arrangement please ?

I'm also interested how you will wire the chargers, so that all batteries in the bank get charged, so please include that too.

 

[TNLI]

Can you post a schematic showing where you would fit diodes on a four battery domestic arrangement please ?

I'm also interested how you will wire the chargers, so that all batteries in the bank get charged, so please include that too.

Yes, but as you are not really interested, you will have to pay me first.
One other thing I missed in my last post is that it's not a good idea to use diodes for battery protection, or to allow you to mix different types of battery in parallel if you have any sort of intelligent charging system. I don't like those type of charging systems as one failed on a friends boat and fried the entire battery bank.

 

[PaulRainbow]

Yes, but as you are not really interested, you will have to pay me first.

I'll have some of what you're smoking please.

One other thing I missed in my last post is that it's not a good idea to use diodes for battery protection, or to allow you to mix different types of battery in parallel if you have any sort of intelligent charging system. I don't like those type of charging systems as one failed on a friends boat and fried the entire battery bank.

Diodes are not for battery protection, that's just foolish. They can fail open or closed circuit. Fuses and circuit breakers are for battery cable protection (note we're protecting the cables here, not the batteries).

It's clear for all to see that you don't actually understand the subject matter, you have read and misunderstood some internet articles and you think you are an expert. Hopefully no one will take any of your posting seriously (seems unlikely). In any event, i've wasted far too much of my time trying to correct some of your errors, i'll leave you to it. Have a nice weekend.

 

[TNLI]

This is a quote from one technical article about diodes failures:

Failure Mode: One Open Diode. Cause: After a diode shorts, it will burn open if no other failure occurs first. There may actually be a broken or loose connection external to diode which will have the same effect as an open diode even though the diode itself has not failed open.

If you look up the data sheet for a heavy duty diode it should state what that current is. Diodes are not a sensible way of protecting circuits due to the cost of replacing them, it's just a bonus when used for battery protection.
I would not recommend that anyone fit diodes unless they have no real choice due to mixing battery types in parallel, as it's an expensive option that complicates the wiring and results in a slight loss of performance. The main reason I mentioned their use is that a number of technical articles mention them.

In the end adding too many batteries in parallel is never a good idea, and it is worth reading some of the technical articles about those potential problems. This one is about how to connect a single charger, as that is often done incorrectly:

how-configure-battery-bank - Web (windynation.com)

 

[PaulRainbow]

This is a quote from one technical article about diodes failures:

Failure Mode: One Open Diode. Cause: After a diode shorts, it will burn open if no other failure occurs first. There may actually be a broken or loose connection external to diode which will have the same effect as an open diode even though the diode itself has not failed open.

If you look up the data sheet for a heavy duty diode it should state what that current is. Diodes are not a sensible way of protecting circuits due to the cost of replacing them, it's just a bonus when used for battery protection.

No one in their right mind would put diodes in a parallel battery bank on a boat. They would serve no useful purpose, would not be anything ike reliable for "battery protection" (FYI we don't fit circuit protection to batteries to protect the battery, it's there to protect the wiring, nothing external to the batteries can protect the battery from internal failure) and would cause unnecessary voltage drop.

I would not recommend that anyone fit diodes unless they have no real choice due to mixing battery types in parallel, as it's an expensive option that complicates the wiring and results in a slight loss of performance. The main reason I mentioned their use is that a number of technical articles mention them.

That's nonsense, you have repeatedly suggested fitting diodes. Fitting diodes "due to mixing battery types" is just more nonsense, diodes will not overcome any of the issues that might be caused by mixing battery types. There are actually installations that benefit from having mixed battery types in parallel and i mean dramatically different battery types. People who design such systems and actually understand how they work know how to connect them, why they are connected and know how to make use of the differences, rather than those differences causing an issue.

It's obvious you have been reading various "technical articles", but it's equally obvious that those articles have come from different industries, some of which will differ to marine installations and that, more importantly, you have misunderstood what you have read, in many cases. So much so, that you now consider yourself an authority on the subject.

In the end adding too many batteries in parallel is never a good idea, and it is worth reading some of the technical articles about those potential problems. This one is about how to connect a single charger, as that is often done incorrectly:

how-configure-battery-bank - Web (windynation.com)

I'm well aware of how to connect batteries in parallel, as is just about every regular reader of PBO, i've posted multiple system schematics on here, multiple times. You cannot cite problems caused by incorrect installations as being reasons for not installing batteries in parallel. Correct installation doesn't have those problems and a parallel bank has less catastrophic failure potential than a single battery.

 

[Alex_Blackwood]

On one in their right mind would put diodes in a parallel battery bank on a boat. They would serve no useful purpose, would not be anything ike reliable for "battery protection" (FYI we don't fit circuit protection to batteries to protect the battery, it's there to protect the wiring, nothing external to the batteries can protect the battery from internal failure) and would cause unnecessary voltage drop.



That's nonsense, you have repeatedly suggested fitting diodes. Fitting diodes "due to mixing battery types" is just more nonsense, diodes will not overcome any of the issues that might be caused by mixing battery types. There are actually installations that benefit from having mixed battery types in parallel and i mean dramatically different battery types. People who design such systems and actually understand how they work know how to connect them, why they are connected and know how to make use of the differences, rather than those differences causing an issue.

It's obvious you have been reading various "technical articles", but it's equally obvious that those articles have come from different industries, some of which will differ to marine installations and that, more importantly, you have misunderstood what you have read, in many cases. So much so, that you now consider yourself an authority on the subject.



I'm well aware of how to connect batteries in parallel, as is just about every regular reader of PBO, i've posted multiple system schematics on here, multiple times. You cannot cite problems caused by incorrect installations as being reasons for not installing batteries in parallel. Correct installation doesn't have those problems and a parallel bank has less catastrophic failure potential than a single battery.

Paul, Banging heads and brick walls come to mind. I should go and have a nice single malt. More productive and you will feel better!

 

[TNLI]

First of all let me emphasise that using protection diodes is only of interest if you are combining batteries of different types, it's also problematic in terms of the size of the diode and slight voltage type if you might need to use your house batteries to start the engine. It also complicates the charging circuit as that will also need diodes for each battery or group of similar batteries.

One question I have, is has anyone used one of these:
Victron - Argo Diode Battery Isolators - 80 to 180A options (ARG080201000) | eBay
This appears to be a more efficient unit than a normal split charging diode unit, as it use Schottky diodes.

This is another useful type of unit if you are not using real deep cycle batteries:
Victron Energy Battery Protect 12/24-Volt 65 amp : Amazon.co.uk: Automotive

In general terms if you want anything electrical or electronic to be reliable, stay well clear of the max listed rating. If anyone knows a better way of mixing batteries in parallel, please post a link or diagram, rather than negative posts and opinions.
Finally I would remind anyone constructing a large parallel battery bank that in the end using another battery selector to divide them up is definitely the way to go,
I'm not against combining batteries of the same type and age in parallel, but anyone doing that should be aware that when one of the batteries starts to fail, you will need to change all of the batteries in that bank to get it to function efficiently,

PS: I don't base my posts on anything I find in the internet, but what I try to do is provide links to confirm my opinions and to provide more information.