charging starter battery

[geronimo]

Why do some boat builders connect 240V chargers only to main batteries and not to the starter battery. That battery is charged only by the alternator.

It would seem a good idea to fully charge both battery packs with shore power.

 

[markdj]

Starter battery is never discharged as after the engine starts it immediately gets topped up again.

To charge both you need a charger with 2 outputs or you can use a splitter diode.

 

[halcyon]

Some do some do not.
Sealine for example had two engine batteries ( one for each engine ) and a domestic bank, both engines charging the service bank, mains charger charging the service bank, then the engine batteries when it had surplace power available. That was till around 1991 when they adopted a two battery system, as a cost reduction to bring them inline with Princess and Failine, and only charged the service battery. later around 1996 they went back to charging both battery banks.
You pays your money and takes your choice.

Brian

 

[Guest]

Re: charging starter battery ..... simple solution ...

About £7 at local Maplins ..... charge splitter .....

I fitted one and charger now charges both batterys a treat. No more thinking about switching from one to another etc. for charging. They get each what they want.

It's left connected at all times .. and engine alternator looks after whichever battery is connected via the main 1-b-2-off switch.

 

[steve_cronin]

Quick answer - Cheap & simple chargers cut production costs

They think that you'll probably use the boat to get from one marina hook-up to another and that if you only stop one night then why bother re-charging the starter battery. Reasonable assumption in most cases but a proper multi-stage, multi bank charger is preferrable if you are using a power windlass and/or a bow thruster off the engine battery for <u>long periods</u> before berthing and not running your engine much the following morning to re-charge. Not a very likely scenario in the UK.

Splitter doides used with a mains charger WILL put some charge into both battery banks but since the voltage on the battery sides will be lowered, the charge time will be much extended and full charge mightn't be achieved at all. A multi-output charger with battery sensing and a smart alternator regulator is the only answer to the "problem". However, you might not actually HAVE a problem.

Steve Cronin

 

[Guest]

It is the same reason cars don't come with 240v leads. After a 2 week holiday you expect your car to start on the first day back to work. If it does not then a temporary charging arrangement helps. Same idea with boats. The discharge rates of batteries are very low as long as they are truly used just for starting and have no other current drains like fancy battery monitors.

Although I have a means to charge my starter battery, I have never needed to, even after 6 months on the hard in Napa valley. So the question is why complicate the system? If the only time it would be used is in a marina/berth with power then a temporary arrangement to top up a battery is adequate.

 

[bedouin]

One of the issues is that modern "Smart" battery chargers sense the state of the battery they are charging and adjust the output to suit - this cannot be done if you are trying to charge two batteries at the same time (at least it can - but you have to duplicate all the sensing and control circuity = more money).

As others have said, your starting battery should never actually need charging but if by any chance it is flat you can always use the domestic bank to start the engine.

 

[waterboy]

The Victron charger/inverters charge the service batteries with an additional terminal for an optional trickle charge to the starter battery. Seems to work fine.

 

[timchapman]

If you've money to spend try this

 

[bedouin]

That looks like a smart VSR - which combines two battery banks - it is not appropriate to use that with any sort of smart charger that varies its output voltage according to the sensed state of the battery

 

[Guest]

The static sense current of that relay is 12mA. So over 6 months that is 52AHours. So unless it can be disabled it, is impossible to leave the boat without power. The only way to disable this one is to remove one or both main fuses, depending on dual sensing. The supply must come through one of the A or B terminals.

There are other issues as well. The manual shows two fuses on the line containing the VSR. These would be large. However the negative line to the VSR is tiny and so in a fault condition of the sense electronics, it would not be able to blow the main fuses.

VSR design should keep the high power and sense circuits well separated with fast fuses in all sense and low power lines. The diagram in the manual is in my view a terrible example of unfused electronics on boats. Unless there is some hidden trip or fuse that is not obvious in the manual.

Final point is that on simple systems VSR work. But once the complexity rises then all the switches start seeing each others actions. It is interesting on boats with voltage sensitive loads like fridges and charge combiners and either wind or solar regulators with charged batteries. They can start fighting when the fridge or VSR thinks the voltage is high enough to start using power. This means all charging sources are switched on as the battery suddenly goes below the threshold voltage. If it is light winds or dull then there is not enough to keep the battery voltage high enough. So the load disconnects. Then the generating sources charge the battery up to the point the fridge thinks the engine has been turned on again. And it goes on and on and on. In this time (since most have a short time delay) the VSR has seen these fluctuations therefore it is connecting and disconnecting the starter battery to the house circuit. So every few minutes or so the fridge gets to run partially off the starter battery!

OK, now I'm confused. Conclusion: On complex yachts VSRs are a bit of a pain.

 

[Guest]

I think KDDpower will have something to say !!

SolarNeil .... just waiting for KDDpower to answer your post !!

 

[halcyon]

Re: I think KDDpower will have something to say !!

I cannot comment on there use of fuses. We fit a small circuit breaker in the VSR controll unit to protect electronics and relay coils. If using a solid state shunt we pick up voltage at the battery terminal and again fit a circuit breaker.

With regard to the complex system the solar panel, wind gen or battery charger are connected to the service battery. If the fridge cuts in the voltage will drop, depending on the size of fridge and charge source,this may be small or large.
Now I can't talk for all but our VSR systems, these cut in at a user preset voltage(13.8v factory set ) and drop out at 13.00 volt. Therefore on a dull day it is not likely that the relay will cut, unless a large solar panel in which case it will probably have enough power to supply fridge without large volt drop. On a bright day the relay will probably be in and there is enough power to supply fridge. If relay is engaged the engine battery becomes part of the main bank, and when the fridge drops out the power used is replace by the charge source. Once a relay drops out it will not come in until the service battery gets back up to it's cut-in voltage, which will not be possible until the load that caused that drop is removed, thus no cut in drop out cycle. Also as the unit also charges the service batteries from the engine, and provides link start from service bank, it gives a simpler system.

With regard to power usage, as the relay is normally located after the isolater switches, when you leave the boat you turn them off, thus no drain. If you leave the batteries on you have the solar panel, wind gen or charger on, so power loss is easly made up.

Will that do ?

Brian

 

[geronimo]

Thank you all very much. I have learned a lot although the last discussion has become too technical for me.

My charger has a different output for the starter battery which will deliver Wu characteristic (not that I know what it means but for service batteries it does Wae/Wu) and it will only charge with 2 Amps as opposed to 50 Amps for the service batteries.

According to this discussion I may either connect it or not. But if the alternator can never charge the battery more than 80%, as they tell me (hence get an Adverc, they say), then I shall never have the starter battery fully charged. That will shorten its life I am told.

To charge the batteries fully I either seem to need some device beside the alternator, or connect all batteries to the shore power charger.

 

[Ships_Cat]

I think if you measure the charge current from an alternator to your cranking battery after a normal start the charge rate will only be a few amps even if one had an external regulator on it because the battery is still essentially fully charged. Also, if extended cranking, for some reason, or some other load (say use of a windlass on it without the engine running) depletes the battery further then a low charge rate from a charger is fine as is always plenty of time to recharge. So low charge rate from charger is always fine.

With respect to your comment on the alternator not charging to more than 80% (and assuming that you are talking about the cranking battery) then it should never be discharged less than a few percent below full charge so the possible problem is irrelevant.

However, should extended cranking or some other thing deplete the cranking battery severely, generally the internally regulated alternator will bring it up to full charge with an extended run as alternators fitted to marine engines are usually able to provide a charge rate sufficient to charge the relatively small capacity of a cranking battery (and also due to their higher charge acceptance rate due to their thinner plates). That situation cannot be compared to the need in the case of trying to fully charge high capacity cycling service batteries without a stepped charge controller.

As examples of those last points the alternator in your car will fully charge your car battery no problem at all, even from fully flat, and will do that in a comparatively short time. The same applies on your boat. On our own boat we can charge our service battery bank off either the normal internally regulated alternator normally dedicated to the cranking battery or from their own high capacity alternator through its stepped charge controller. We find that the cranking battery alternator will easily fully charge the cranking battery but will NEVER EVER even after very long motoring runs fully charge the service batteries.

So with respect to connecting your shore charger to the cranking battery I personally would not bother. The cranking battery can be charged from its own alternator easily and relatively quickly even in the case it becomes more depleted than normal, assuming one can start the engine. As another (Lakesailor I think) said this can always be done from the service batteries in an emergency and if any cabling was to be undertaken then the best thing is to put in a permanent but key locked interconnection so that one can crank from the service batteries in an emergency. A little thought will also show that solution gives the opportunity of charging the cranking battery off the shore charger (in the unlikely event it was ever needed) with no extra cabling required.

John

 

[William_H]

It is possible the engine alternator only takes the engine battery to 80% however this combination has been used for cars since the beginning of self starters and batteries seem to have a decent life so don't worry about the life of your engine battery. Coming back to the original question if you don't have problem why worry? Bear in mind however that your engine battery can not be expected to last forever. If it fails to start the engine and it is over 3 years old it is probably dud. good luck....olewill

 

[Guest]

80% ..... so ??

Many boats without fancy charge boost / controllers etc. manage to have cranking and domestic battery's survive for years .... 5 ... 6 ... sometimes near 10 years ...... Mine lasted well past 6 years each and were still useable when changed out for peace of mind.