Basic volts question for battery use

[skipmac]

Paul Rainbow refers to my "preferred procedure" for managing a system comprising two batteries linked by a 1,2,both, off switch, which I described in #11.

Not so much intended to restrict charging to one battery at a time, more as a way of only having one battery in service at a time, The designated engine start battery for engine starting only and the domestic services battery for all the other loads. Done properly this will ensure that the engine start battery is always recharged after use but can never be discharged by inadvertently running the domestics from it.

I am quite happy for the banks to be parallelled, by switching to "both" after the engine has been started and for them to be charged together but then one has to remember to switch to the domestics battery only when the engine is stopped.

OK. Went back and read #11. It is a better procedure in some ways than charging on both which requires remembering to switch to one battery for house use after charging, however your procedure has it's own concerns. Arguably the most potentially damaging (and an issue you clearly point out) is switching from one battery to the other while charging ONLY via Both instead of via Off to avoid blowing the alternator diodes. Even switching properly I would recommend idling down the engine while switching.

Your procedure also still requires remembering a switch change IE from one battery to the other while charging vs from Both to one battery when charging is done. Your procedure will reduce the risk of discharging both banks but increases the risk of not charging one bank if you forget to switch during charging. This will usually be a better "problem" since the battery that wasn't charged will in most cases not be fully discharged and so still usable for cranking.

It should be clear from these discussions that there is no perfect, foolproof method for using a 1-2-Both switch unless the operator is perfect in remembering the process. From experience I can attest that this ain't me, and from jumping and towing fellow boaters over the years it seems I'm not the only one. The ideal which is pretty simple and not so expensive (maybe £200 for parts and cables if you DIY) is to use a voltage controlled, automatic combiner like the Xantrex Echocharge (about the only Xantrex product I would recommend), Yandina Combiner or similar.

Pretty much what Vics said. My reasoning for not charging using the boat setting is that ;

a) If you forget to set it back to the domestic batteries when you stop you can end up with no way to start the engine.

Agree, however as I noted above, one still has to depend on memory for switching something.
In Vic's method instead of the risk of discharging all batteries by house use you risk not charging one of the batteries (or banks). If one battery is reserved exclusively for starting then it will probably be well charged anyway if one forgets to switch since starting uses so little of the capacity unless the boat is used infrequently and it has self discharged.

b) If on battery fails it can discharge to good one and, again, no way to start the engine.

Also agree but if one battery seriously fails during charging it will probably cause more problems that failure to start. If not a serious failure like a shorted cell, then during charging one would still be charging the good battery and unless one forgets to switch away from Both then one battery will be charged. This does bring up the point that depending on the condition of both batteries, if one is not charged enough to crank the engine it could indeed discharge a good battery if switched to Both to crank. Whether or not to use Both or to switch just to the "good" for starting will be a judgement call.

That's why i'd support Vics "prefered method". I'd also highly recommend getting rid of 1-2-both switches and have permanently separate circuits where both battery banks get charged via a VSR or similar.

In this I see we are all in complete agreement.

DISCLAIMER: This procedure comes with risk of damage to the charging system and possible fire, sparking or injury!!!! Don't try this if you aren't fully aware of how to do it and the risks associated.

In an emergency if you have two mostly discharged but not dead or shorted batteries that don't have quite enough oomph to crank the engine (diesels only) there is a trick you can try. Rewire two 12V batteries into series to get 24V and use that to start the engine. You should disconnect the field to the alternator when doing this. Once the engine is running, reconnect the batteries into parallel 12V and reconnect the alternator.

 

[VicS]

Thanks all, I ran the engine on battery one in idle at around 1000rpm for about 20 mins, then did the same for battery 2, that brought them up to 13v, from around 12.1. I will adopt vics suggested use of the 1/2 switch until the electrics are redone and will then add a Sep engine battery, and solar power. Plenty of space for panels on her. There is always some load as the new depth sounder is wired permanently in, it was the only way they could do it.
Ran the engine again briefly this morning to put charge back into batt 2, and am keeping batt 1 for engine start.

One more question, can I turn the selector switch from 1 to both once the engine has started and running? I thought touching that with the engine on was a big no?

If "1" is the start battery then you can select that and start the engine.

I'd let the battery recharge ... guided by the voltmeter reading

Then, yes, you can move to both ........ leave it there to charge both batteries together if you wish ......or move to "2" to put that in service and charging on its own. If you remain on "both" you must remember to select "2" when you stop the engine

What you must NOT do , NEVER, EVER, is to switch to "Off" while the engine is running. If you do you will very likely cause a voltage surge which will blow the diodes.

Consider all the BMWs speeding along the motorway nose to tail. If something suddenly blocks their path there is a big pile up with bits of BMW going everywhere.

If your engine is running and the alternator is busy charging the battery the electrons are speeding along the wires, like the BMWs on the motorway. If you open an isolator switch that suddenly blocks their path, there is big pile up of electrons which causes a voltage surge. The voltage surge will destroy the diodes.

 

[PaulRainbow]

DISCLAIMER: This procedure comes with risk of damage to the charging system and possible fire, sparking or injury!!!! Don't try this if you aren't fully aware of how to do it and the risks associated.

In an emergency if you have two mostly discharged but not dead or shorted batteries that don't have quite enough oomph to crank the engine (diesels only) there is a trick you can try. Rewire two 12V batteries into series to get 24V and use that to start the engine. You should disconnect the field to the alternator when doing this. Once the engine is running, reconnect the batteries into parallel 12V and reconnect the alternator.

Been a while since i've done that one. Used to do it with petrol engines in the days before electronics and CANBus, 12v coils would stand 24v and no doubt gave a really good spark to get the old engines running on a cold and damp morning.

 

[lw395]

Charging one battery at a time pretty much means a lot more idle running of the engine.
Ideally you'd charge each battery for several hours to get even close to fully charged.
The current drops off progressively while charging at a constant voltage, as happens with a normal alternator circuit.

I can't see what's so hard or mysterious about remembering to switch the switch when you start or stop engines, previous generations managed OK.
For sure there are shiny automatic solutions which are very nice, but many people would be better off spending the cash on either more batteries or solar panels. Or maybe go sailing and spend it on marina fees and get some shore power?

Just like the 0-1-both-2 switch, the more complicated solutions are a pest when boat owners don't understand them fully or when they go wrong.
Or when people try to use them outside of their design parameters.

None of the systems is fool proof and different boats with different needs will favour different solutions.

 

[PaulRainbow]

I can't see what's so hard or mysterious about remembering to switch the switch when you start or stop engines, previous generations managed OK.

Fine if you ignore the potential failures that can leave you unable to start the engine.

Much better to have separate circuits and split charging. IMO

 

[Heckler]

If "1" is the start battery then you can select that and start the engine.

I'd let the battery recharge ... guided by the voltmeter reading

Then, yes, you can move to both ........ leave it there to charge both batteries together if you wish ......or move to "2" to put that in service and charging on its own. If you remain on "both" you must remember to select "2" when you stop the engine

What you must NOT do , NEVER, EVER, is to switch to "Off" while the engine is running. If you do you will very likely cause a voltage surge which will blow the diodes.

Consider all the BMWs speeding along the motorway nose to tail. If something suddenly blocks their path there is a big pile up with bits of BMW going everywhere.

If your engine is running and the alternator is busy charging the battery the electrons are speeding along the wires, like the BMWs on the motorway. If you open an isolator switch that suddenly blocks their path, there is big pile up of electrons which causes a voltage surge. The voltage surge will destroy the diodes.

Audi s!

 

[VicS]

Audi s!

Audis in the provinces maybe. Beamers in this part of the country. Interspersed with Range Rovers, in particular those funny squashed ones.

 

[PaulRainbow]

Audi s!

Few weeks ago, just about to open the door, in a layby on the side of the A14, a white Audi came through the layby at a substantial rate of knots, using the layby to undertake some lorries !

 

[skipmac]

"Load does not mean in gear it means working harder e.g. at higher revs." That is backwards, increasing RPM does not equate to being under load, it just means everything is going faster. Putting it in gear and driving the propeller is under load, making it drive a large alternator/generator is putting it under load.

Your experience with engines is showing. This is my understanding as well.

I'm not suggesting that you run it at 2000 RPM, i'm saying fast idle. In other words, just a few more RPM than no throttle.

I have monitored alternator output on various engines and again, this is exactly correct. Off hand I don't recall the exact numbers but more or less 90% of max alternator output if I rev from idle (about 900 rpm on my Westerbeke) to maybe 1200-1400 rpm.

 

[skipmac]

Charging one battery at a time pretty much means a lot more idle running of the engine.
Ideally you'd charge each battery for several hours to get even close to fully charged.
The current drops off progressively while charging at a constant voltage, as happens with a normal alternator circuit.

Agree. This is exactly my logic for charging all banks at the same time.

I can't see what's so hard or mysterious about remembering to switch the switch when you start or stop engines, previous generations managed OK.

Not mysterious at all but even though I am almost perfect I have forgotten to switch away from Both more than once and have run down my batteries a couple of times (in the far distant past before adding a auto combiner). For some that never forget this can work but for the rest of us not always. Come into a port late and tired,
deal with crowded anchorage, some minor problem, stowing away all the gear and it's easy to forget the battery switch.

For sure there are shiny automatic solutions which are very nice, but many people would be better off spending the cash on either more batteries or solar panels. Or maybe go sailing and spend it on marina fees and get some shore power?

But it isn't that much cash. I set up an auto combiner for about USD$150 total.

Just like the 0-1-both-2 switch, the more complicated solutions are a pest when boat owners don't understand them fully or when they go wrong.

Auto combiner is actually less complicated than the switch. Once it's installed it's totally automatic.
Nothing to set, switch, change or mess with.

Or when people try to use them outside of their design parameters.

Buy the right kit, install it correctly and this is a non issue.

None of the systems is fool proof and different boats with different needs will favour different solutions.

A quality auto combiner is about as reliable and fool proof as it can get. I have participated in discussions with marine electricians that have been installing them for years with approaching zero failure rate. I guess one could think up some convoluted different needs situation but any boat that has an engine to crank and house loads to run that is large enough to have more than one battery could use one.

 

[lw395]

Not sure exactly what kind of device you are promoting as an 'auto combiner', but I am aware of several people having VSR type devices fail, and one or two others having premature failures of the start battery through using them (caused by overcharging the start battery).
There's a lot of stuff on the market these days which is designed for solar power off grid installations then punted out on the marine market where the problems are different. There are also older designs which don't take into account that many yachts have a lot of solar power these days.
Increasingly, a lot of yacht owners don't know exactly what they have, what it's designed to do or how to get the best out of it.
ISTR that years ago you could buy a little warning circuit that alarmed if you left the battery switch in 'both' while they weren't being charged.
But nobody really needed it so it went off the market.

For some people, a battery-to-battery charger is a very good solution and can be cost effective too.

 

[skipmac]

Not sure exactly what kind of device you are promoting as an 'auto combiner', but I am aware of several people having VSR type devices fail, and one or two others having premature failures of the start battery through using them (caused by overcharging the start battery).
There's a lot of stuff on the market these days which is designed for solar power off grid installations then punted out on the marine market where the problems are different. There are also older designs which don't take into account that many yachts have a lot of solar power these days.
Increasingly, a lot of yacht owners don't know exactly what they have, what it's designed to do or how to get the best out of it.
ISTR that years ago you could buy a little warning circuit that alarmed if you left the battery switch in 'both' while they weren't being charged.
But nobody really needed it so it went off the market.

For some people, a battery-to-battery charger is a very good solution and can be cost effective too.

Here are links to three, well known, very well made and reliable units. Reports from marine electrical professionals that install these indicate as I mentioned before of a very, very low failure rate. They are after all, pretty simple devices with very little to fail.

http://www.xantrex.com/documents/Ac...er/Echo-charge-OwnerGuide(445-0204-01-01).pdf

http://www.yandina.com/c100InfoR3.htm

http://www.balmar.net/products/digital-duo-charge/

As far as overcharging the start battery, with these types of combiners that is a non issue. The question comes up very often, "What happens when I combine a large, discharged battery with a small, fully charged one?. Won't the smaller battery be overcharged?"

The answer is no it won't. With a correctly operating charging system (not set at too high a voltage) the charge acceptance will be largely self limiting. The battery with the lower charge will have a lower voltage and lower internal resistance so most of the charge will be directed to that battery. Look at the standard, dumb charging system in your car. The alternator is regulated to put out a constant voltage usually around 14-14.2V and yet your car batteries don't die an early death due to overcharging even if you drive daily for hours and hours.

Below is a link to a longer explanation of this issue.

http://www.yandina.com/combInfo.htm#Q32

Not sure what kind of battery to battery charger you refer to. If a device that simply connects two batteries (or banks) to allow a charged battery to charge a discharged one, this would indeed result in premature battery failure due to chronic undercharging since a fully charged battery has a voltage of +/- 12.6V which is far too low to properly charge another battery.

 

[lw395]

...

As far as overcharging the start battery, with these types of combiners that is a non issue. The question comes up very often, "What happens when I combine a large, discharged battery with a small, fully charged one?. Won't the smaller battery be overcharged?"

The answer is no it won't. With a correctly operating charging system (not set at too high a voltage) the charge acceptance will be largely self limiting. The battery with the lower charge will have a lower voltage and lower internal resistance so most of the charge will be directed to that battery. Look at the standard, dumb charging system in your car. The alternator is regulated to put out a constant voltage usually around 14-14.2V and yet your car batteries don't die an early death due to overcharging even if you drive daily for hours and hours.

Below is a link to a longer explanation of this issue.

http://www.yandina.com/combInfo.htm#Q32y.

The link is simplistic twaddle.
You have a start battery, let's say 50Ah. Assume it is fully charged initially. You start an engine with it, let's say 200A (average) for ten seconds.
That's about half an amp hour, so the battery is still 99% charged.
So, if you were charging this battery optimally, you would soon turn the volts down to float.
That's not going to happen when you've got a house bank paralleled with it, that has been taken down to say 80% overnight.
The disparity between the state of charge of the engine and house batteries can give the engine battery a very hard time.

The comparison with cars is interesting, the average use pattern of a car is to drive for an hour or a few hours, on average twice a day.
A typical car battery life is anything from 30,000 miles to 100,000 miles, but there is increasing incidence of early failures.
Taking the 100k miles as a 'hopeful' figure, that's about 2000-3000 hours.
Which is a lot of years motoring, but only 4 months on shorepower or maybe anything from 8 months to a couple of years with a serious solar set up.
So, it's quite easy for the engine battery to have its life seriously reduced by VSR strapping it to the house battery if you have solar, wind or shore charging.
In the scheme of things engine batteries are cheap, but it's annoying when you're in the bum end of nowhere.

 

[lw395]

Not sure what kind of battery to battery charger you refer to. If a device that simply connects two batteries (or banks) to allow a charged battery to charge a discharged one, this would indeed result in premature battery failure due to chronic undercharging since a fully charged battery has a voltage of +/- 12.6V which is far too low to properly charge another battery.

The battery to battery chargers I'm familiar with take in anything from 10 to 15V and step it up, down or across to give a three stage intelligent battery charge to optimise battery performance. Some have inputs for wind, solar and 'system' power.
I'm not claiming to be up to date in the 'consumer marine' market in this area.
For an amateur system you can get a step-up converter on ebay for the price of a pint of beer. You could then regulate that at float volts.
Life is actually a little easier if you are always stepping up or down, e.g. charging 12V engine from 24V 'house' or 28V airframe from 12V 'vehicle'.

The down side of B to B chargers is cheap ones have a small current, so perhaps not suitable if you make heavy demands like running the bowthruster off the engine battery.

 

[PaulRainbow]

Fit a dual sensing VSR, connect the alternator to the engine battery and the solar controller to the domestic bank. If the VSR fails, not the end of the World, the engine battery will pretty much take care of itself and when you run the engine it tops the batteries up. The solar controller will keep the domestics charged as much as possible. Battery monitoring will promptly pick up the failure and it can be fixed in a few minutes. If you're off grid for a few days you can always bypass the VSR, but that does leave you with the potential issues i mentioned earlier regarding battery failure etc. But, it's an emergency and needs must.

There are of course other solutions than a VSR, but a VSR is a cheap and simple solution that will work for just about anyone with a 1-2-both switch.

 

[skipmac]

The link is simplistic twaddle.

Well you may call that simplistic twaddle but perhaps because the writer, a EE that has been designing and building marine electrical equipment for probably 30 years, wrote it for misinformed laymen. [COLOR]

You have a start battery, let's say 50Ah. Assume it is fully charged initially. You start an engine with it, let's say 200A (average) for ten seconds.
That's about half an amp hour, so the battery is still 99% charged.

You did get the math and terminology correct.

So, if you were charging this battery optimally, you would soon turn the volts down to float.
That's not going to happen when you've got a house bank paralleled with it, that has been taken down to say 80% overnight.
The disparity between the state of charge of the engine and house batteries can give the engine battery a very hard time.

The comparison with cars is interesting, the average use pattern of a car is to drive for an hour or a few hours, on average twice a day.
A typical car battery life is anything from 30,000 miles to 100,000 miles, but there is increasing incidence of early failures.
Taking the 100k miles as a 'hopeful' figure, that's about 2000-3000 hours.
Which is a lot of years motoring, but only 4 months on shorepower or maybe anything from 8 months to a couple of years with a serious solar set up.

Interesting math but you do need to factor in that battery life is determined by charge cycles, depth of discharge, charging regimen and age as well if you want to start getting technical.

So, it's quite easy for the engine battery to have its life seriously reduced by VSR strapping it to the house battery if you have solar, wind or shore charging.

Well again, no it isn't because as I said before, if the start battery is mostly charged (as it will normally be) then it will have a higher voltage, higher internal resistance and the bulk of the amps produced by the charging source will be directed to the battery with a lower state of charge and therefor lower resistance. Very basic Ohm's Law calculation.

In the scheme of things engine batteries are cheap, but it's annoying when you're in the bum end of nowhere.

Having had a dead battery when anchored in the far south Bahamas at least 100 miles from the nearest settlement I can certainly agree with you on this point.

We can toss out theories and irrelevant numbers all day but at the end of the day these devices have been on the market for probably 20-30 years and I'm making a wild guess here, tens of thousands installed and I have not heard of any significant increase in dead starting batteries in the boating world. All other arguments aside, these combiners are used and highly recommended by top marine electrical technicians, technical advisers for the ABYC and some of the leading marine electrical experts in the world (ever heard of Nigel Calder). Even though I do have an EE degree I don't pretend to have the expertise in this field that these guys bring to the table but I do know enough to read and understand their logic, research and test results and made my decision on what I think is the best option.

 

[skipmac]

The battery to battery chargers I'm familiar with take in anything from 10 to 15V and step it up, down or across to give a three stage intelligent battery charge to optimise battery performance. Some have inputs for wind, solar and 'system' power.
I'm not claiming to be up to date in the 'consumer marine' market in this area.
For an amateur system you can get a step-up converter on ebay for the price of a pint of beer. You could then regulate that at float volts.
Life is actually a little easier if you are always stepping up or down, e.g. charging 12V engine from 24V 'house' or 28V airframe from 12V 'vehicle'.

The down side of B to B chargers is cheap ones have a small current, so perhaps not suitable if you make heavy demands like running the bowthruster off the engine battery.

Did some internet searching for DC-DC converters. Hardly the price of a pint if you get one with equal capacity to a automatic combiner. 100 amp units were $200 and up. I can buy a 100 amp combiner for half that.

 

[PaulRainbow]

Did some internet searching for DC-DC converters. Hardly the price of a pint if you get one with equal capacity to a automatic combiner. 100 amp units were $200 and up. I can buy a 100 amp combiner for half that.

I have some cheap DC-DC convertors onboard, two running 14v TV and soundbar, one running 19v laptop and two making high powered USB chargers. All were very inexpensive, none come even close to being able to charge a battery at any sort of amperage. One that might handle my alternator output would cost a significant sum, as you say.

Given the price and simplicity of a VSR, i don't see the point. My VSR is made by Victron, it's intelligent (microprocessor controlled), will take 120a and costs about £40.

 

[lw395]

Did some internet searching for DC-DC converters. Hardly the price of a pint if you get one with equal capacity to a automatic combiner. 100 amp units were $200 and up. I can buy a 100 amp combiner for half that.

Why would you need to charge the engine battery at 100A? It will only draw a few amps from an alternator after the first couple of seconds.
Something rated at a couple of amps would recharge from starting and be voltage limiting in minutes. We build such things into equipment.
100A is not enough to run the starter motor or some other loads like bow thrusters.
We've had threads on here in the past from people who've had problems with these things. Which could be down to misuse, the VSR is not the right solution for what they are trying to do.
But for an increasing number of people, the overcharging of the start battery could be an issue. Ask any battery manufacturer how many 1000s of hours of overcharge is OK. If it was OK, battery chargers wouldn't need to knock back to float voltage.

Conversely, if the system does not have enough power going in to keep up with house demands, the start battery can be undercharged.
I guess that's why Victron make programmable VSRs too!

 

[skipmac]

Why would you need to charge the engine battery at 100A? It will only draw a few amps from an alternator after the first couple of seconds.

Usually one would not need to charge a starting battery at 100 amps, but occasionally it can happen.
If the boats been sitting a while without solar or other way to maintain the batteries the battery could self discharge.
Maybe working on the engine and run the starting a number of times. Maybe a new starting battery that needs charging up. Also, even if the starting battery is mostly charged on startup the initial inrush current can be many amps. Since a 100 amp combiner isn't that expensive then why not get one with a bit more capacity than needed. In most situations too much is better than not enough.

Something rated at a couple of amps would recharge from starting and be voltage limiting in minutes. We build such things into equipment.
100A is not enough to run the starter motor or some other loads like bow thrusters.

First, running loads isn't the primary intent of a combiner, however, if one is running a large load like a thruster from a battery connected to a combiner the battery can supply the load.

We've had threads on here in the past from people who've had problems with these things. Which could be down to misuse, the VSR is not the right solution for what they are trying to do.

Well, nothing is perfect. Any piece of kit can fail. All I can say here is that marine professionals install them for long term customers. If they caused as many problems as you seem to think I doubt these guys would recommend them.

But for an increasing number of people, the overcharging of the start battery could be an issue. Ask any battery manufacturer how many 1000s of hours of overcharge is OK. If it was OK, battery chargers wouldn't need to knock back to float voltage.

Already answered this question at least twice. Overcharging is NOT an issue. The battery with lower charge will take the majority of the charge, a charged battery in parallel will take very little. Do you know Ohm's Law?Can you calculate current in a parallel circuit? AND, as I also pointed out, the voltage from a smart charger isn't that high, even in bulk charge mode and not that different from the voltage of a standard auto alternator.

Conversely, if the system does not have enough power going in to keep up with house demands, the start battery can be undercharged.

Remotely possible I guess if one has very high house loads and a significantly under capacity charging system. However if that is the situation then an undercharged start battery will be one of the least of the problems.

I guess that's why Victron make programmable VSRs too!