The Moody 40 Oldie and Batteries

My immediate thought to adding diodes in series to drop the voltage from your battery charger is that it won't work as expected.

The charger requires feedback from the batteries in order to "throttle" the charge rate. The diodes would block that feedback voltage/current to the charger.

I'd be looking at "adjusting" the charger to provide the required output. Is the charger a commercial brand or a home brew device? Is the circuit diagram/service manual available?

Thank you, this makes sense to me too. The charger is a "special" brand boat battery charger of respectable age too, but working well for Lead Acid (flooded). I will collect the data in the coming days.

Dear dvmdsc, I have used diodes to drop voltage, - when using a car alternator to charge deep cycle batteries, a higher voltage is needed so the alternator can be tricked to charge to a higher voltage by inserting a (1 or more) diode in series in the line to the field. The technique is also used to protect starting batteries in case of a second battery running appliances, eg in a caravan, but the technique fails in that the voltage drop is bad for the second battery as it will usually require a higher voltage to fully charge. Why use gel cells? they are not as flexible as flooded so usually don't last as long. I would recommend Flooded Tubular Positives for the appliances, and maybe explore the newly developed Spiral Wound lead batteries for the starting, - very energy dense and long lasting. Cheers, Geoff Thomas

I too have a sailboat with batteries for lighting and assecories. Before deep cycle batteries were available we used regular wet cell auto batteries with no problem. Charging was done by a home made charger of an exotic design (my father the electrical engineer). When deep cycles became available we switches to them, still no problems either in draw-down or charging. Would always be fully charged after charging and then a rest as indicated by a volt meter and a hydrometer.

About 25 years ago we replaced the outboard motor to a new one and it has a 3 amp alternator on it. Hooked this up to the electrical system and it tops the battery off when necessary or will do a slow full recharge if lights were left on erroniously. Old charger is still working properly when needed.

On several occasions when my car battery has died during the off season I have placed the boat deep cycle in my car/truck and used it there for as long as 3 years with no problems. Most often I would forget it was there due to its lack of needing attention.

FROM MY EXPERIENCES I would say that you are ok to charge all the batteries, both regular and deep cycle from the same charger, with proper battery isolation between the banks. without any noticable problem.

Have you actually tried charging the gels from the deep cycle charger? It would be interesting and helpful to know what your results were.

At my electrical/electronics bench I use a fused car battery or deep cycle battery as my "12 v" source to test mobile equipment and supply chargers of that voltage, I charge it constantly with either a dying battery charger or a 1-1/2 amp battery maintainer. Made my own fuse box and now have about 5 things supplied from it.

Diodes in the charging circuit will work but not as accurately predictable as you would like.

Good Luck, Old Salt

Replace your charger. A high quality charger will give a lot of life to your batteries.

lighthasmass is absolutely correct. Make sure the charger matches the battery you are using. A float voltage that is off by more than 0.010 or 0.020V over temperature for your particular cell type can make the difference between a 5 year life and a 20 year life.

This is a perennial problem for my clients. Many of them are also upgrading flooded batteries installations and do not wish to replace the old dumb chargers with a new "smart" charger. The principal difference between flooded and sealed Gel or AGM lies in the float voltage. If you continue to use the older charger one solution is to shut off the charger shortly after the battery voltage reaches the absorption stage. Typically this was set for 14.2 but some models like the McCarron could be as high as 14.5V

It is the duration of outgassing that does the damage.

Be mindfull that when the sealed batteries outgass the cell is destroyed. Loss of internal pressure kills the recombinant gas process. It has been my experience or rather that of my clients that GEL batteries are less tolerant to over voltage than AGM. This may be a result of the gelling process which AGM does not have. We also discovered that many chinese battery manufacgturers do not distinguish between AGM and GEL. When we encountered problems with one installation where AGM had been specified I noted in the fine print mention of fumigated silicon. The factory had substituted GEL witout notice. AS far as they and the yacht builder was concerned it made no difference. I insisted they change it and since then the yacht has travelled to the MED from Asia without battery problems.

Only GEL batteries use silicon powder as a gelling agent. AGM uses a starved electrolyte in a glass matt as the interlayer between plates but no inert filler.

This seem to allow a bit of latitude in bubble formation and electrolyte changes to accomodate out gasssing .

For optimum results the charger should be configured to suit the battery technology. The charging algorithm is more than just a slight change in output voltage. We did suggest owners of our combination inverter / charger use a reduced voltage if they changed to AGM technology but this is a stop gap measure and will result in premature battery failure.

Thank you for your advises:

As far as the batteries - I still want to use 2 regular Lead Acid starter batteries in bank 2 for starting the diesel engine.

The gel batteries have only 2 wires coming out the sealed battery. Roughly a #8. The charger has a proven record of reliability and is still as new on the market.

The charging problem is dual - and charging the Lead acid batteries and sometimes at the same time also the gels. The sailboat has made 2 Atlantic crossings and power on board needs to be very reliable. During these trips I use a 500 Watts wind generator and 2 X 120 Watts solar panels - the generator is only on when anchoring and only for limited time - when using electric appliances.

When I am sailing I can monitor the batteries perfectly with a digital multimeter. The problem is when I am not there. The lead acid batteries will evaporate water and at the same time the gels will probably be destroyed because of a too high voltage to top off.

That is why I thought to bring the max voltage down, only on the gels with diodes.

You can put hydrocaps on your Pb acid batteries to recover lost H2O, but, I think, you need a second charger to handle the chemistries of two different battery banks.

Dropping the maximum voltage will simply result in under charged batteries which in turn leads to early sulfation and then premature battery bank failure.

I realize you want to save money so go buy flooded batteries again and if you wish install the hydro caps. They do work.

I have only been involved with lead acid battery charging systems for 20 years so what do I know? My advice is only worth what you paid for it.

If you really think GEL is the way to go then buy them. Remember once the sale person gets your money they really do not care any further. If you have a problem its you that will be paying the consequences for a long time.

I have no vested interest in convincing you which brand or type to buy. I only want to offer sound advice based on my experience.

What about flooded and sealed? I have an opportunity here with a local manufacturer to get 6 batteries for a cheaper price than BCI 29. These cost here normally $270 each, bonded (import tax free $169.00) and the AG.. I can get for $140.00 because they come with only bolts of 3/8". I can handle these connections. They are degassing without maintenance. (glass coated)

Flooded and sealed? Are these by chance 'maintenance free' automotive style. If you check modern automotive charging systems you will find many of them now charge at 13.8 not 14.2V While this prevents over charging and out gassing it does mean the batteries typically last only 3 years which is good for them bad for the consumer.

He builds these for himself for boats and heavy duty machinery. They come like a kit with plates and fiberglass bags and mats that he fits in the compartments. They are half starter types and deep cycle. I didn't buy these yet - we start preparing for hurricane Irene and I hope I can keep the boat afloat till it is passed. I'll try to make some pictures while he is handcrafting these. There is no way to fill these up afterwards. Thank You.