CHARGING BATTERY

[robert]

I have a services and a starting battery on board but only the starter battery is charged by engine (2gm20). If I use jump leads to connect both when engine running so as to charge both will I risk damage to altenator . Would be very grateful for an opinion.

 

[Seapepper]

Suggest that you get a changeover switch - Vetus makes one-
It will allow you to switch both batteries off or barr 1 on or batt 2 on or both batteries on. I use one on a 1gm10....no problems.

 

[tonyleigh]

Yes - fit a switch to offer charging to either. It has the added advantage of being able to use both batteries for starting if you need a little extra whoompf. However, I know there are risks, to the battery I believe, if you charge both at the same time.

 

[PuffTheMagicDragon]

Not Enough

Changeover switches, by VETUS or by less-expensive-but-just-as-good Taiwan, are not enough. Turning the switch to 'BOTH' will allow one battery to discharge into the other; this could possibly leave you with two semi charged batteries. You'll also need to remember which one to charge more. Fit a diode splitter. It does not have to be 'marine' (i.e.expensive). I recently fitted an american one that is intended for trucks (lorries?) It has a 75Amp capacity and is built into a chunky heat-sink about the size of four cigarette packs stuck together. It cost me less than 30 pounds Sterling so you'll probably be able to find the same thing for less in England. It is really 'fit and forget' ; one lead (IN) goes to the alternator while the other two (OUT) go one each to the positive terminals on the batteries. I wish I'd done it earlier.


Wally

 

[david_bagshaw]

In answer to your question "If I use jump leads to connect both when engine running so as to charge both will I risk damage to altenator ", the fixes suggested are the full time answer,

Unlikely , but watch out for the following problems,

1 lack of ventilation and sparks igniting the charging gas on disconnection.

2 lack of ventilation to the alternator while charging.

Diode splitters

I would add often the starting battery is connected to a certain terminal as the makers often arrange the internals so the engine start Batt is charged more first.

Joining batts together

we have had no problem in having battery banks paralled for greater capacity, our banks are each of 4 batteries. ie Lighting comprises 2 in series to make a24 volt"group" then 2 groups paralled to make more capacity.& engine start is the same again.

It does lead to the theory if one batt fails it leads to discharge from the rest of the pack, well we have had 5 & 7 yrs service from each bank, and the one that failed at 5 was due to boat yard abuse in one winter .

Hope that helps





David psTake a look at www.yachtman.co.uk

 

[dick_james]

Re: Not Enough

But then there is the volt drop across the diodes (about 0.6v) and with the alternator probably machine sensed, the batteries will never get fully charged....isolating relay, battery sensed alternator or remote regulator - adverc, sterling etc.
Dick James

 

[charles_reed]

Answer to your question - probably no risk.

But - if you are to progress from Heath Robinson to something like technical sanity.

1. Fit a 3 way rotary switch on the output side of the batteries.
2. Fit a splitting diode into the charging circuit.
3. Replace the inadequate voltage regulator on your 2GM20 (has it the 35amp or 55 amp Hitachi alternator?) with a "smart" one such as TWC or Adverc.

 

[Guest]

This is the expensive [but very correct] solution!

May I offer a 'possibility'? I am not familiar with the 2gm20 but I am guessing that you don't have a very high output alternator? Get yourself a relay which will handle the full alternator current and install it so that when energised it will effectively connect the battery positives and wire the relay coil to the ignition 'ON' so that the relay connects the 2 batteries when the engine is running. The cross current between batteries is not that high enough to cause a problem unless you switched the ignition on and left it without the engine running for a long time. It is also recommended to connect the alternator output to the relay terminal that the start battery is connected to ...

Batteries [most] by nature limit current as they are charged and it is really only over-voltage which will overcharge them! Otherwise your car battery would be damaged when driving long distances with lots of electrics on as the alternator could be hammering out 50A to feed your lights, wipers, hrw, etc but the battery could be fully charged, brand new, etc - it may 'accept' a small current but as long as the voltage didn't rise excessively it would not be damaged - and the principle is the same! An alternator is designed to put out a voltage and a regulator restricts that to around 14volts and that is ALL an alternator regulator does. The battery's state of charge determines how many amps it will allow to flow and as it charges up this current will fall - you can't force any more current through it without raising the voltage as well!

 

[Guest]

Making it all automatic

We sell thousands of battery combiners per year in the USA. They monitor both batteries and if either starts charging, it automatically puts the other battery in parallel. When charging ceases, they separate the batteries. They draw no current when not "combining" and about 150 milliamps when combining. They have time delays to prevent short cycling, and overload sensing to protect the relay from the heavy currents that can flow from battery to battery when it first turns on. The 50 amp version sells for about $50 USA discount and handles alternators up to 100 amps. I believe there are equivalent products in the UK.

You can read all about them on our web site at www.yandina.com. Check out the FAQ page and you can download owner's manuals with circuit diagrams, installation instrucions etc..

tech@yandina.com

 

[brianrunyard]

This exactly what I've done, and have never had any problems. I always run with it switched to the starting battery initially to put back what the starter has taken out, then switch over to the service battery, I've installed an ammeter to show when the charge into the starting battery has dropped off. Works for me!!!!!

 

[Guest]

The 'Bible' advice is that you should not move this switch while the engine is running [even if it does have field contacts] as you will still [probably] induce voltage spikes which could damage any electronics on board!

 

[Guest]

Most alternators push out at least 35 amps,check yours.Each battery has a capacity,say 100 amp/hour,the normal charge is at the ten hour rate,in other words you devide the capacity by ten to get the charging current.So for 2 x100 a/h batteries you need an alternator capable of supplying 20 amps.The batteries are connected +to+ & -to- paralel.

double trouble