Mixing batteries

[Guest]

Cheap powerpacks ...

Have a couple of pals bought the cheap ones ..... for emergency start etc.
Started car and boat first few times .... but soon gave up the ghost and basically couldn't take the punishment. They got relegated to portable powerpacks for PC's / GPS etc.
Those guys advised me if I was to consider a powerpack - get a serious professional job ...... cough - seen the prices !!!!

<hr width=100% size=1>Cheers Nigel http://groups.yahoo.com/group/gps-navigator/ http://groups.yahoo.com/group/searider/

 

[bedouin]

Re: That\'s sensible advice...

It depends a bit on what you've got at present. If you've got a conventional alternator and no diodes, then a 1-2-both switch gives the simplest solution and allows you manually to select how to charge each bank. Also with a conventional auto alternator it is unlikely to put out more than 13.8V which is not really going to hurt the RedFlash even if it is connected for a long time.

The problem comes when you use a smart alternator regulator (e.g. Adverc, Sterling) which can put out up to 14.8V, which I think is too much to put through the RedFlash. In that case you definitely need a mechanism for controlling the charge to the battery. The easiest way I can think to do this is to fit a second regulator just for the RedFlash - for example one designed to regulate the output from high-powered solar cells or wind generators.

This would be easy to connect - by attaching the "input" to the regulator to the output from the split charge diodes. The problem is it would need to have a high current rating (e.g. >20A) and those don't come cheap - about £60-£100.

The only other solutions I can think of involve a soldering iron /forums/images/icons/smile.gif

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[bedouin]

Re: Simplest solution...

A word of caution about VSRs. As far as I know most of these work by switching the two banks into parallel once there is sufficient charge in the starter battery.

However what is wanted in this case is to switch the engine battery completely out of circuit once it is fully charged - my brief search has not foud a VSR that works that way.

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[bedouin]

Re: Cheap powerpacks ...

I thought as much. I've got one as a general purpose portable 12V supply, but it only contains a 17Ah Golf Cart battery - I imagine a couple of goes trying to start the diesel would kill that.

There is one available that uses the RedFlash batteries - but that is comparatively expensive. My low-tech solution is to carry round a cheap car battery from Halfords!

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[pvb]

Please don\'t use a 1/2/Both switch...

Please don't use a 1/2/Both switch, Will. These contraptions are the source of numerous problems, and really have no place on a modern boat. It's just so easy to inadvertently leave the switch in the "Both" setting and then find that your starter battery is discharged (particularly with a small capacity battery such as a Redflash), or indeed to forget to select "Both" and then find that the coolbox won't work. In contrast, the VSR is a fail-safe solution, which will safeguard the charge integrity of your starter battery (a vital factor on a powerboat). There's little difference in cost, and the VSR can be fitted out of sight. No contest!

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[pvb]

Beg to disagree...

I'm not sure how you came to believe that "what is wanted in this case is to switch the engine battery completely out of circuit once it is fully charged". Will certainly didn't suggest this, and it's a peculiar thing to propose. Apart from anything else, how do you think someone is going to know that the engine battery's fully charged? There's no problem in leaving the engine battery in circuit - the Redflash battery will simply stop drawing current as it reaches full charge.

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[bedouin]

Re: Beg to disagree...

That would only be the case if you used a standard car alternator charging at 13.8V. I charge my domestics at 14.8V. In my usage the engine starting battery gets little drain and so is effectively always fully charged.

No sealed battery will take 14.8V for hours on end when already fully charged. If I put the RedFlash on the other side of the diode splitter with no additional protection it would die a horrible death very early.

It is trivial to know if a lead acid battery is fully charged - simply monitoring the terminal voltage is adequate in this case - how do you think automatic charges do it?



In the normal run of things I start the engine maybe twice a day - say 30 secs each time with a starter motor drawing 100A. Total consumption starting engine 2Ah

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[pvb]

Relevance...

Maybe you're overlooking the fact that this part of the thread is responding to a specific query from Will, whose profile details the boat he owns and its engine type. I'd like to help him make the right decision for his particular circumstances. I think that Will probably has the standard alternator on his Volvo TAMD22P, and is unlikely to have a "smart" regulator fitted. In this case, his alternator is unlikely to put out more than 14.4v and won't give any problems over long periods connected to a Redflash. The voltage you charge your batteries at is, in the circumstances, irrelevant.

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[bedouin]

Re: Relevance...

You are making a lot of assumptions that you don't bother to state. If he does have a higher charging voltage than 13.8V your advice would fry his batteries. Not what I'd call good advice - unless you work for a battery manufacturer.

Will responded to my post about my thoughts about fitting RedFlash to my boat - I amplified on my post in a way that was accurate and doesn't make any assumptions at all about his set up.



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[pvb]

Never let the facts get in the way, eh Bedders?...

My only assumption, clearly stated, was "I think that Will probably has the standard alternator on his Volvo TAMD22P, and is unlikely to have a 'smart' regulator fitted." The basis for this assumption is that, in a previous post, Will said he only had 1 battery on his Ombrine.

Your assertion that a higher charging voltage than 13.8v would "fry his batteries" is patently ridiculous. And I don't work for a battery manufacturer, so it's no good shouting "conspiracy". If you bothered to check the facts before rubbishing my posts you'd see that the Redflash will cope with charging voltages up to 14.7v - check out the <A target="_blank" HREF=http://www.dmstech.co.uk/images/lifeline.pdf>Technical Information for Redflash batteries</A>, where it says "Voltage at the battery terminals during charging should be between 13.9 Volts and 14.7 Volts for a 12 Volt system..."

Of course, the advice I've just quoted does come from a battery manufacturer, so maybe.....

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[pvb]

Oh dear, Will...

I'm afraid my attempts to suggest a simple, trouble-free solution for you are being frustrated a bit. It seems that Bedouin is a bit out of sorts at the moment. Rest assured that if you follow my advice you'll have an elegant, unobtrusive, fit-and-forget solution. If you go down the route of the archaic 1/2/Both switch, etc, you'll be constantly fiddling and worrying whether the thing's set properly. If you're concerned about charging voltages on Redflash, and don't believe the published information, you can email their technical people for advice at info@dmstech.co.uk



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[bbilly]

Re: Oh dear, Will...

PVB and Bed, Thanks for the animated debate which stimulates thuoght and enriches my knowledge. Yes I have the standard alternator and voltage regulator and my major concern on the boat is not running my battery flat and being stranded - can't think of anything worse happening to me so that's why Iv got the redflash as a simple emergency backup (low space req. and long long shelf life). However it seems they start buses with capacitors (which then recharge) so the redflash could probably be a permanent solution for starting. Ive got a couple of insulated boxes for the beer and wine but ice is not always available and warm beer is disgusting so id like to have an elettrical one. The idea of the VSR sounds great but Beds comment "As far as I know most of these work by switching the two banks into parallel once there is sufficient charge in the starter battery" sounds like I could end up with 2 flat batteries? ". Could I reasonably expect a portable fridge approx 25 litres to run allday on 1 deepcycle battery.

Will


<hr width=100% size=1>"If you're too open minded your brains fall out"

 

[pvb]

Re: Oh dear, Will...

The VSR only connects the batteries in parallel when the engine is actually charging and the engine battery has reached a voltage of 13.8v under charge, not when there is "sufficient charge in the starter battery", so you couldn't end up with a flat starter battery.

Your portable fridge would probably run most of the day on a single battery, depending on ambient temperature (and it gets a bit warm in Rome!). It would help if you cool it down well at home first, and in the car en route to the boat, then keep it out of the sun as much as possible.

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[halcyon]

Re: Never let the facts get in the way, eh Bedders?...

What puzzels me is that people are happy to drive a car all day, most now run at around 14.8 volt, some to 15 volt plus, but worry about running the boat for a couple of hours.
Red flash say they are self regulating for charge amps, thought all batteries were, alternators do not produce volts but watts, the voltage you see is based on battery state. A flat battery will take 13.00 volt to take it's charge current, depending on battery type this can be large or small, but will only be limited by the watts ( volts X amps ) that the alternator can produce. This is also limited by the current drawn for boat sytems, thus if you have 50 amp at 13.0 volt available, but draw 20 amp for nav equip, fridge etc, you only have 30 amp for battery charging. As the battery capacity rises, the volts ( emf in old terms ) rises to maintain charge amps, if amps are limited,by alternator output, then voltage will still rise at a slower rate, and charge amps will fall. This will carry on till a voltage of approx 16 volt is achieved, but at this voltage you have very heavy gassing, so the alternator is set to stop producing a output above a set voltage. Thus the amps appear to slowly fall once the reg point is reached, upto this point you can only get what the alternator will give. If you have blocking diodes you are reducing the regulation point thus the amps you can put in are limited. Fitting smart regulators will overcome this, but will only give more amps once you exceed the regulation point. Thus if your alternator regulates at 14.7 volt, and have a Red flash battery, you will gain next to nothing, or exceed the recommended battery voltage.
Afraid in the end battery charging is a very complicated thing, altering one little bit in the chain, can alter many other factors, the outcome can be positive or negative.

Brian

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[ditchcrawler]

Re: Oh dear, Will...

You appear to have taken over my thread Will.It would be courteous would it not to ask your own questions.It is frustrating to log in & see that I have another batch of replies only to find that others are fighting over your question& not mine.
Regards
Ditchcrawler

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[bbilly]

Re: a meeting to discuss topics of PUBLIC concern

Ditch, courteously - sorry if you feel i am encroaching your territory and filling your inbox but this is the essence of a forum. <<a meeting to discuss topics of PUBLIC concern>>. You have concerns similar to mine and PVB and Bedouin as well as others have contributed lots of interesting information, requirements, opinions and experience that hopefully are valuable to a wide range of users as well as you and me. I personally am researching the VSR + Redflash Starter and replacing my wet starter for a deepcycle for services. Same space, simple and fail safe.

My thanks to all and especially to Ditch for the original post.

<hr width=100% size=1>"If you're too open minded your brains fall out"

 

[bedouin]

Re: Never let the facts get in the way, eh Bedders

All I can say is that more than one independent supplier who I spoke to (including those that supplied Red Flash) said that a constant 14.8V would fry the battery and didn't recommend a sustained voltage above 14V into a fully charged battery.

No one I've spoken to, not even the manufacturer, recommends pushing 14.8V into the battery.

However, clearly you know better...

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[halcyon]

Re: Never let the facts get in the way, eh Bedders

Have a feeling it may be crossed wires.
From the web site alternators running upto 14.7 volt are ok, mains chargers are up to 14.7 volt 3 stage.
Thus continuous is mains charging, and should be below 14.0 volt, alternator charging is intermitant, and can be 14.7 volt.
Check they were referring to mains, if not ask them to explain the dmstech web site tech details for charging.

Brian

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[bedouin]

Re: Never let the facts get in the way, eh Bedders

Yes - and no. There is an added complication that I didn't explain above:

The document states "Most battery control systems fitted to yachts adjust the charge voltage automatically to ensure that the correct voltage is maintained at the battery terminals so that the battery recharges properly.....Providing the charge voltage is correctly regulated no current limit is required...

So it's true that if your battery control system is "battery sensing" AND you have if configured to sense the Engine battery then you will not have a problem with the Red Flash - as it says above. However there is a problem.

The common battery sensing alternator controllers (Adverc, Sterling) can only sense the condition of a single battery bank. If you set the system up to sense the engine battery, they will switch to a maintenance / float charge as soon as that bank gets fully charged, meaning that the domestic bank will take much longer to charge - and in fact may never reach 100% charge. If on the other hand you sense the domestic bank then you will not be regulating the charge voltage correctly for the Engine bank, which can damage the Red Flash battery.

Also in order to get those precious Ah into my domestic bank as fast as possible I charge them at 14.8V, which is higher than the RedFlash can take. So if I am to install the RedFlash battery in addition to the domestic bank I need some form of independent regulation of the charging of the Red Flash

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[pvb]

Barking, completely barking....

I'm not sure if you're just s**t-stirring, or whether you've simply lost the plot, but you keep changing your story.

You rubbished my advice to Will, saying (2115 on 17 Oct) "If he does have a higher charging voltage than 13.8V your advice would fry his batteries. Not what I'd call good advice - unless you work for a battery manufacturer."

I responded to that, pointing out that the Redflash battery would safely take a charge up to 14.7v, and providing a link to the manufacturer's technical information to support this.

Then you replied and said (2240 on 18 Oct) that "a constant 14.8V would fry the battery." Well maybe it would, but who said anything about charging at 14.8v? The day before, you were claiming that 13.8v would fry the batteries - now it's 14.8v.

To make matters worse, you then accuse me by saying "No one I've spoken to, not even the manufacturer, recommends pushing 14.8V into the battery. However, clearly you know better... ". Just in case I'm going mad, maybe you can remind me in which post I said that a 14.8v charge would be OK.

On second thoughts, don't bother. The sooner the Special Needs forum re-opens, the better. Hopefully then you'll rejoin the sad conspiracy theorists and leave this forum to people who actually want to help others.


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