charging batteries on board

[owen]

ill try again. can anyone advise on battery charging from a mains charger on board. can I charge both batteries together or do they need to be done separately. do the batteries need to be disconected while being charged thanks in antic

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[Trevethan]

If you buy a decent charger you can usually charge 2 or 3 battery banks simultaneously and at the same time power your onboard 12 volt systems.

You need to look at the size of your batteries and buy a charger that is suitable. I have 400 amps of batteries and I have a 50 amp Sterling charger/power pack The thing stays on all the time we are pklugged into the pontoon.

Try giving Sterling or Adverc a call and tell them your situation they can tell you what you need.

I also carry a cheapish £50 quid car battery charger bought from halfords that charges another battery on a seprate circuit that I have yet tied into the rest of the circuit -- its a three stage smart charger rated around 4 amps and looks after the battery that powers the electric heads (80 amp hour) -- obviously doesn't get huge usage!

My Sterling can charge 3 banks. You are supposed to link any unused +ve outpouts to ones that are used. I run a single negative from one of the battery negatives -- these are always joined, then two +ve leads, one to each of the positive terminals.

Not sure if this is the right way but it means that teh batteries are connected to teh charger no matter what position the battery switch is in.

The charger is connected to the boat's 240 system on a dedicated circuit using a fused 3 pin plug away from the batteries so I can quickly disconnect power should something unpleasant happen, however the charger says it has all kinds of safety cut outs etc etc etc

You are supposed to keep the cables between charger and batteries a short as possible, mine are about 1 metre long and Keep the charger fairly close to the batteries. Mine are about 1 metre long and are the sort of thickness you find on motorbike starters. maybe 1 cm sq in cross section (maybe a bit over done) but don't forget the negative can carry pretty big loads.

I keep my charger separete from the batteries, in an area that is dry and has good ventilation.

hope helps,

Nick

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[philwebb]

Hi Owen, You can charge your on-board batteries in parallel as long as your charger
will give enough current. You will have to make sure that nothing else is in circuit
before you charge your batteries. If not take off the clamp terminal off the positive
battery terminal. The charging voltage is higher than 12volts and so could damage any
sensitive equipment left connected. Regards, Phil

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[Eric_the_unready]

That reply doesn't make any sense, when the engine is running the alternator charges at 14+ volts - you don't have to disconccet any equipment then - why should it be any different with a battery charger?

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[steve_cronin]

If you have a domestic battery and a starter battery you could indeed charge them both from the same car -type charger by simply connecting the charger outlet to both positives and both negatives. However there is no guarantee that they will both charge fully. Indeed it is unlikely as being of different capacities and maybe different levels of health the stronger battery might take most charge.

There are available however, chargers dedicated to marine use with separate outputs for different types of battery which will ensure proper charging for each. unless there is a significant load connected there is no need to disconnect the batteries before charging, indeed this type of charger is usually "built in" as part of a shorepower system. However a connected load like a refridgerator or even a few lights will delay or even prevent full charging of the batery to which it is connected.

Such chargers often use "smart" or "intelligent" technology to achieve a really full battery by breaking the charge cycle into stages. Their are various charging regiemes used by different manufacturers due to a lot of differing thoughts on the subject.

I had one made by Sterling Marine Products on my last boat which worked well but I have chosen a "Dolphin" for this boat because the terminals on the Sterling made fitting fiddly since they were too small & close together for my liking. Those on the Dolphin are much better laid out and the charger in general, together with it's smart remote control panel just fits in better on this boat.

There are many makes out there not just the two above including Mobitronic, Hitech, Techpro, Mastervolt, Truecharge and several more.

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[Chris_Rose]

check out merlinpower.com, they know everything there is too know about batteries

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[iacle]

Another question

I always disconnect one of the terminals on the battery I'm charging to protect the alternator. Is this neccessary if the battery selector is off ? I'm worried the alternator is still connected even when the switch is off.

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[LORDNELSON]

Re: Another question

I suppose that everyone's electrical circuits may be a little different so any reply to your question should be treated with caution. My experience is that when I have shore power connected the battery charger is automatically "on" and charging all three batteries (360 Amp-hour, with smart type charger) and I use the 12 volt circuits (lighting, instruments mainly) at the same time if I am on board; have been doing this for years and so far no problems. Hope this helps.

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[TeamLBN]

Again Another question

Seems that this is the place to talk about charging batteries - can anyone advise an electrical novice on what piece of kit is required to allow charging of a single 85Ah battery from a 5hp outboard which has a charging circuit? I am told that the output is AC - does this mean I need and inverter / converter / widgit / thingy etc?

Thanks

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[MedMan]

Re: Another question

I am not sure I understand why you are concerned that your alternator is still in circuit. It is not a problem I have considered as I have House and Starter banks separated by blocking diodes and my built-in charger is connected direct to the House Bank. The diodes thus prevent any current from the charger reaching the alternator, but why would it matter if it did?

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[steve_cronin]

Re: Again Another question

If it is AC, then to convert to DC for charging, the simple answer is that you need a rectifier of some sort. However you first have to know the waveform of the output. Most small outboards offer a single extra coil on the magneto which is energised once a revolution by the permanent magnet in the flywheel. This would give a single phase output and would be relatively simple to rectify with a cheap battery charger rectifier from Maplins. Some bigger outboards a few years ago had an array of coils so as to get as much output as possible - up to 15amps (but they needed a special three phase rectifier) whereas you will be lucky to get five with the engine revving hard.

If this is a Honda outboard, some of them already have a rectifier installed. Look for a grey square unit with fins in the wiring from the magneto. On the Honda I had it had a screw through the middle of it and it was screwed (as I remember) to the outer shroud of the engine and it's output went to a rubber non-reversable socket through one side. This socket had a rubber protective cover with a retaining tag. If this is how yours is you have a 12volt DC output

Unfortunately with a lot of these outputs they are just that:- 12volts and they even loose some of this in the rectifier but you need more to charge a 12volt battery fully. You need around 14.4volts. This is why such outputs are often called "lighting outputs" rather than charging outputs. Something is better than nothing though so it's worth a try.

A regulator is often not fitted since the output is so meagre and the use of the engine so intermittent, overcharging is unlikely. It's not like a solar panel or a wind charger which are running for half a day or more at a time. Motoring across the Channel might heat up the battery a bit (with sufficient voltage output) but on the Honda the advice was "If concerned, unplug the connection"

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[bigmart]

Re: Again Another question

You will need a rectifyer to convert from AC to DC & a Voltage regulator to prevent the battery being overcharged. Try your engine manufacturer for the apropriate items.

Martin

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[smb]

In answer to your questions, yes you can charge more than one bank at once and no you do not need to disconnect any loads. However this is subject to certain proviso's, the main one being suitably matched components.

For information here is a rundown of my system which thus far has served 2 seasons of busy weekends and holidays in the channel without any signs of impending trouble.

Starter bank 110ah, domestic bank 3 x 170ah, all open lead acid type.
Shore power charger is Sterling 50A 3 stage model. All three outputs are commoned (by me) at the charger and connected to domestic bank only via a shunt. I leave the charger connected to shore power all week as a rule, but for peace of mind I prefer to see it has reached the float charge stage before leaving the boat.

I only use the starter battery for starting. She normally starts first time after very few turns and I usually run the engine for 20 mins plus, therefore I reason the alternator can (and does) take care of the starter battery.

I connected through the shunt so I can read net charging current on an Adverc DCM, thus showing what is actually reaching the battery after any domestic load (fridge/lights/cd etc) has had its share.

If I need to put a top up charge on the starter battery (ie ashore for three months) I can parallel them via the 1,2,both switch and heavy guage cable and fuses (same goes for emergency starting off the domestic bank). Only once they have stabilised at the same voltage do I turn the charger on, not before, but I think this is being over cautious.

The 90A alternator charges both in parallel via an Adverc controller, a splitter diode and in the case of the domestic bank, through the aforementioned shunt. That way I can regulate engine revs to ensure optimum output from the alternator and minimum charging time when at anchor.

I don't remember if it's an exact copy but I got most of the idea from the Adverc website.

Hope it is of some help. I also hope there are no experts out there just itching to tell me it's all wrong and I am living on borrowed time.

Steve




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[jessica]

Nick
I am thinking of fitting a Sterling 20 amp charger for my 2 * 100amp batteries
I wondered about mounting it in the main cabin by the main switch panel with the incoming shore power. This would be approx 2 metres from batteries.
Are they noisy with the cooling fan on? Don't want sleep disturbed!
Do they need much ventilation around them for cooling?
Any problem with electrical interference on GPS etc?
Any advice welcome


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[smb]

Hi,

My 50A version has two fans and probably makes as much noise as a typical PC cooling fan.
It is fitted under the saloon floor in the engine bay where it can be a bit warm, and there is no ventilation other than the combustion air intakes. The fans tend to cycle on and off but only ever in the 50A bulk charge phase and I have to open the hatch to be sure it is the charger.

I've never noticed any interference with GPS or other instruments. Come to think of it, by the time I have got shorepower connected I already know where I am, have written up the log, turned off the instruments and opened a can of something so it's likely I have never checked. I will next time out though.

Steve


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[ccscott49]

Re: Another question

No need to disconnect, the alternator will not be harmed. even if the switch is left on.

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[halcyon]

When you say batteries, do you have two in parallel, or two seperate banks, ie engine and service. If you have two in parallel, just connect up a charger to pos and neg, as a guide you need a charger 10% of battery capacity ie 10amp for a 100 amp bank. Going larger will charge up the batteries quicker, but you get less capacity, the faster you try and charge the less capacity you get.
A car charger is ok if you have a small bank, and only want to charge intermitantly, as they have no top end cut off, and you can then get battery damage due to high voltage. Also remember that most car chargers are rated RMS, that means that a 10 amp rated charger will give you around 4-5 amp.
If you have a large capacity, then go for a marine charger, which should be capable of running on full output for long periods without damaging batteries. As long as it will charge to a peak voltage of around 14 6/ 14.8 volt, and offers a float charge around 13.6 volt for maintainance you should be ok. All the different systems will not make much difference to you.

If you have two banks, then if you a bi-directional relay, then connect a single output to the service battery. it will then charge and supply service loads. When this gets up to a resonable recharge level, it will put the engine battery on charge, droping out when charge ceases. If you have blocking diodes, then you need a dual output charger, though this may be a single regulator feeding two blocking diodes to give two outputs depending on charger. This means that both banks are charged at the same voltage, were you have independent output regulators, each bank is charge at a voltage dependent to there charge state.

There are a thousend answers to your question, it all comes down to battery size, and your intended use.

Brian

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[halcyon]

Re: Another question

The alternator is a three phase AC generator, this is rectified by two diode banks ( there is a third but not relevant to us now ), these are a pos and neg bank. These effectively give you blocking diodes to back feeding, so you will do no damage to the alternator.

Brian

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[jackho]

My opinion is to charge them seperately.
I'm assuming you are using a normal car type batttery charger. I wouldn't get into the hassle of bridging to parallel - besides the individual batteries may have different characteristics.

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[halcyon]

It will not have much effect the batteries not being the same. For all practical purposes if the batteries are wired in parallel, the batteries will take the current they can.
The battery voltage is due to the internal battery resistance, as the battery is charged so the resistance rises, therefore the voltage to move the current through the battery rises. Once the peak voltage ( or regulation voltage ) is reached, the current will tail of as resistance carries on increasing (Ohms law), till a trickle charge is reached. Thus a flat battery put on charge will be 13.0 volt, as charge rises, so will voltage upto around 15.5 volt ( varies to type of battery but a working guide ). Between 14.7 and 15.5 the rise in voltage is steep, thus little gain in current is acheived, but there is excesive gassing, (starts around 13.8 - 14.0 volt )
Back to the story, the battery with the lower resistance will set the voltage, while the current will be inrelation to resistance, ie more to low resistance less to high. Normally the differences are not large, so the difference in current is not great.
This resistance is what gives you your alternator output voltage, until it reaches it's regulation point it will give you all the output that it can. Once the regulation point is reached current will tail as above, alternators regulating at 14.5 volt are thus not going to give you conciderably more recharge above this point. It is the drop in voltage from fitting of blocking diodes, 0.6 to 1.2 volt which lower your peak voltage to around 13.6 volt, thus at this point your current tails of to almost zero. Or reduces your recharge capacity from around 80% to 50 %, which is also why battery live is reduced as well, little charge, but deep discharge.

The above is a bit simplistic, it has that many variables that it would take a complete book, but if you work on keeping the batteries above 60% capacity, and charge a little often, you will not go far wrong.

Brian

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