Different Battery Types/No Regulator

A30_John · Post by **A30_John** » Thu Mar 31, 2005 11:45 pm

I bought a boat last Fall which I'm preparing for Spring launch. The boat came with two deep cycle batteries of unknown age/quality/useful life remaining. One of the batteries is number "1" on my switch, and the other is number "2". The charging system does not have an external regulator.

I'm hesitant to rely on these batteries for engine starting because of their unknown reliability. I'm quite happy to use them for "house" batteries.

I plan to redo the electrical system within the next two years. In the meantime, here's what I'm thinking about doing:

1) Buy a new "cranking" battery (for position "1" on my switch)

2) Wire the two "unknown" batteries in parallel as my house bank (for position "2" on my switch).

My question: With no external regulator, would I be risking damage when charging all the batteries together when the switch is in the "both" position? My concern is different battery types, etc.

Based on my research, it lseems that I'd be ok.

Does anybody have thoughts on this?

Thanks

Noah · Post by **Noah** » Fri Apr 01, 2005 12:35 pm

There shouldn't be any real problems with the solution that you are proposing. Internal regulators aren't the worst thing in the world, but they aren't the most efficient either. In this case neither bank of batteries will be getting the perfect charge, but that won't be the end of the world. Especially because the two deep cycle batteries are an un-known quantity. In fact even if you had a smart regulator it wouldn't solve your problem of having two different types of batteries. If you did have a multi stage regulator you would probably set it to charge the deepcycle batteries optimally, and the cranking battery would suffer a tiny bit. You could also use a deep cycle battery with sufficient cranking power to start your engine.

I suppose one other thought is how many amps the alternator is. If you double your amps in the house bank the alternator might not be up to snuff to charge it all depending on the size of the batteries.

Good luck,

Noah

Post by **Tim** » Fri Apr 01, 2005 2:24 pm

Internal regulators tend to be set in such a way that they cover a wide variety of charging situations. Therefore, they're not perfect for anything. On the other hand, they're not usually damaging to anything either.

The setup will work fine, but won't be ideal. Most boats are set up this way.

A30_John · Post by **A30_John** » Fri Apr 01, 2005 3:22 pm

Thanks Noah and Tim.

I'm not sure what my alternator is rated at, but I hope that it would be able to maintain the house bank (two deep cycle batteries in parallel) and a cranking battery. My power usage is low.

As an operating procedure, would folks recommend:

1) Starting the engine with battery position at 1 (cranking battery), then charging battery 1 for a while before switching to 2 to top up house bank. This would keep the batteries independent, thereby preventing cross drain between the cranking battery and the house bank.

2) Starting the engine with battery position at "both", then leaving in that position until engine stops and moving battery switch to 2 (house bank).

3) Something different.

I realize this system is far from ideal. But, since the boat will be completely rewired in the next year or so, I'm looking for a temporary solution that will ensure the engine gets started and I have minimal power available for my vhf and nav lights. When I rewire the boat, I'll plan a better system and buy new batteries.

Post by **Tim** » Fri Apr 01, 2005 6:15 pm

Most standard alternators on small diesels are usually around 55 amps, which is adequate for the sort of battery banks we're talking about.

Standard operating practice for most people with this very typical setup is to use the "both" setting just about all the time, except when the engine's off and you're drawing from your battery power. Then, you should switch to your house bank (2) to, in theory anyway, prevent your starting battery from being drawn down. In practice, this usually works OK.

This is a very rudimentary setup, and it's nice to upgrade when you get the chance.

Figment · Post by **Figment** » Fri Apr 01, 2005 7:25 pm

This setup does have a "downfall situation".

Let's say you've been anchored/moored for a few days, and you've drawn your house battery way down. You start the engine by switching the draw to the starting battery, and then switch to "both" to recharge both.

Now let's say that for some reason you need to shut the engine down ten minutes later. Because the really low house battery has been sucking juice from the starting battery, you might just be left with two mostly-dead batteries and not be able to get started again.
Don't ask me how I learned this.

Really though that's a pretty low-percentage scenario, eh?
Easy fix: Run the charge wire from the alternator to the batteries via a battery combiner, not via the 3position switch.

Post by **dasein668** » Fri Apr 01, 2005 8:18 pm

Figment wrote:Easy fix: Run the charge wire from the alternator to the batteries via a battery combiner, not via the 3position switch.

Essentially, that's what I did with my new system. Well OK, I don't have a 3 position switch at all (I have a separate on-off switch for both house and starting banks), but that doesn't change the set up, really. The other nice thing about using the battery combiner is that you don't have to thing about switching from Both to your house bank. Easy to forget!

While a smart system would be better, I do think a battery combiner is a step up over the regular 4-position switch.

Post by **Tim** » Fri Apr 01, 2005 8:44 pm

The other thing to remember when using a battery switch is to never turn it to (or through) the off position when changing its setting while the engine is running. Doing so can fry the alternator diodes.

Post by **dasein668** » Fri Apr 01, 2005 9:26 pm

Tim wrote:The other thing to remember when using a battery switch is to never turn it to (or through) the off position when changing its setting while the engine is running. Doing so can fry the alternator diodes.

Unless it has a field disconnect. Unlikely on an old switch...

Post by **Tim** » Sat Apr 02, 2005 8:04 am

And even so, why tempt fate? Turn it the other way, just in case!

A30_John · Post by **A30_John** » Sat Apr 02, 2005 12:25 pm

Figment, you have a good point about draining the starting battery when the switch is set to the "both" position with the engine off when there's a depleted house bank. It might also be a problem if the alternator fails and you don't know it has failed. Absent a bank of drained batteries, is there an easy way to know that the alternator has stopped working?

When I redo my electrical system, I'll probably use a battery combiner like Nathan did. (Thanks for the link Nathan. It is giving me ideas for my project next winter.) I've heard it said that battery combiners are just another thing to go wrong, but as long as they can be easily bypassed in event of failure, I would think the advantages would outweigh the disadvantages. I'll certainly have to be careful with my switching in the meantime.

Post by **dasein668** » Sat Apr 02, 2005 6:22 pm

Tim wrote:And even so, why tempt fate? Turn it the other way, just in case!

Actually, I've heard that you shouldn't turn it at all... as occasionally just switching between "on" states could be bad too....

Figment · Post by **Figment** » Sat Apr 02, 2005 10:52 pm

Easy way to know that the alternator has stopped working: ammeter.
Is there an ammeter or substitute "idiot light" or buzzer at your engine's control panel?

A30_John · Post by **A30_John** » Sun Apr 03, 2005 10:19 am

I'll check. I'm pretty sure there would be.

Thanks for your insights everyone. This discussion has been very helpful. My next step will be to obtain a book on the subject. All book recommendations appreciated.