Get rid of the starting battery?????

[waterman46]

A reliable, *dedicated* starting battery that is instantly available without jumper cables, is the most precious piece of electrical and safety equipment on your boat if you have an inboard engine. There is no good reason to look for unreliable, unsafe and inconvenient alternatives.

That said, I enjoy reading these threads, realizing that without creative thinking, humans would still be shivering in our caves.

[valhalla360]

Originally Posted by Alberg30Shill

Because when you inevitably run the house bank to dead thru inattention or exhaustion, you have the ability to start the engine to recharge the house bank.

Or you have a dedicated starter battery and accidentally leave the combiner switch connected and they are all dead.

You can always find a combination of events that fails.

For a small displacement boat with a small engine, the OP has a great option (with a 300-500hp diesel, it gets a little iffy). We did similar on our Gemini but with outboard power, the backup was to pull the cord a time or two...though I suppose the cord could have broke.

The only catch if using the jump pack is to check the house bank. If it's really low, you may be better off disconnecting it and starting straight off the jump pack otherwise, the house bank may quickly pull all the juice out of the backup.

[valhalla360]

Originally Posted by Pizzazz

Isn't all this too complicated? It seems that we all agree two independent battery banks are needed to ensure you do not run out of electricity. Most boats have a off/1/2/both switch. If your main bank is so undersized that you worry about high current draw then just set it to both when running high amp loads. In regular use leave it to House. Simple.

This entire discussion centers around having a separate startup pack that needs to be stored, charged every now and then, managed, wired, etc. I just fail to see what you gain for so much complexity. If your starting battery is oversized, then just undersize it but do leave the 1/2 setup in place.

Actually we don't all agree. A single large bank will outperform two half size banks due to the peurket effect, charging can be quicker as the larger bank can absorb more power even till the end and realistically, if you run separate banks, it presumes as soon as one is dead, you are cranking up the engine or generator to charge not using both, so effectively you have to double your total battery storage for the same daily consumption.

Keeping the jump pack charged is the only significant hassle if you aren't running a generator or connected to shore power periodically where you can leave it plugged into an outlet for charging. A manual method really makes the difference and many diesels

[mikedefieslife]

Originally Posted by Snore

In a perfect world this will work.


Unfortunately, I believe Murphy was an optimist. IMHO, a single dedicated engine battery with an electronic combiner, and manual override switch is bullet proof and ensure you are never in a spot where the engine will not start.

I bet most are using an AGM while their main bank is FLA. Their charger will be set for FLA, so isn't the AGM then never getting the charge profile it wants/needs?

[Wotname]

Originally Posted by roland stockham

On the boat batt ( rather than cars). When you press the start button the batt drops to nominal 8v. If you regularly use a large house bank that can maintain 12v at 100+a you may burn out the starter. If the back is not big enough all you nav gear drops out.

This is not an issue with a series wound motor (i.e. starter motor).
All that will happen is that the stater motor will spin faster thus deceasing the current flow in the windings.

[Bjorn_O]

Originally Posted by skipmac

Unless there is some new kind of capacitor that I haven't heard of there is problem with this idea. A capacitor will leak and loose the charge fairly quickly, as in hours. Maybe new ones are better or maybe there's a new design but unless this problem is solved you can't use a capacitor for long term storage.

I will connect the capacitor to the solar panel with a resistor, with a value so that the leak current is not an issue. There are capacitors with a fairly low leak current that will not be discharged during the night. Supercapacitors have been tested in cars with good results. Having low internal resistance, they can deliver high currents and store enough energy for a couple of starts. They will also be recharged quickly. (I already have a jump start cable to use if the normal battery is empty.)

[guyrj33]

I have one of those LI jump packs in the car, about 6 months after I got it my friends car wouldn't start. So I said I've got just the thing and pulled out the jump pack. It was stone cold dead.
We used jumper cables to start the car.

just one persons experience.

[mikedefieslife]

Probably worth plugging it into USB to charge every month or two. That's what I do with mine, it doesn't hold power indefinitely.

[waterman46]

Originally Posted by Olddan1943

The key is to start the generator and relax as the generator charges the start battery. Once the main engine is running, let the generator and or the main engine charge the house batteries.

Do you have time to charge up your starting battery while that 50 thousand ton tanker is headed at you at 18 knots?

[john61ct]

OMG obviously you have to keep your powerpak charged!

Lead may self-discharge a little faster, but no chemistry claims you just toss it in a drawer and forget about it.

Just leave it on trickle all the time is better than that.

Even if it your third or fourth layer of belt and suspenders, it becomes a mission-critical part of your infrastructure, treat it that way.

If you don't have safety and maintenance routine checklists strictly followed to a schedule, you have a more fundamental problem to address.

[waterman46]

Originally Posted by valhalla360

Or you have a dedicated starter battery and accidentally leave the combiner switch connected and they are all dead.

You can always find a combination of events that fails.

.

For that reason I do not have any switch that bypasses the battery isolator. Such a switch would be undesireable IMHO since it could, as you say, be accidentally left in closed position.

It is possible to run down the starting battery if there is a fault in the battery isolator. In that unlikely case we use a jumper cable to the house bank, then correct the isolator problem ASAP.

[john61ct]

The good ones are combiners (ACR/VSR) not "isolators" which usually implies the use of old-school diodes.

And usually have the self-jumping facility built in.

This one recommended ​ https://www.bluesea.com/products/762..._-_12V_DC_500A

Nothing like this is needed in the designs being put forward here, only if you have traditionally separate banks.

My proposal above, a single Main bank including protected Reserve/starter sub-bank, requires a voltage-adjustable LVD with a much lower setpoint, so 99.9% of the time it all functions as a single bank to maximize Peukert benefits.

This design is only suitable for those with good monitoring gear, paying attention to batts' state of health, striving to prevent any surprises.

Which IMO should be done regardless of the system design.

[skipmac]

Originally Posted by waterman46

A reliable, *dedicated* starting battery that is instantly available without jumper cables, is the most precious piece of electrical and safety equipment on your boat if you have an inboard engine. There is no good reason to look for unreliable, unsafe and inconvenient alternatives.

I agree with this 100% which is why, if I make this change, the jumper battery will be connected permanently to the starter circuit ready for immediate use.

[skipmac]

Originally Posted by mikedefieslife

I bet most are using an AGM while their main bank is FLA. Their charger will be set for FLA, so isn't the AGM then never getting the charge profile it wants/needs?

Actually my current setup uses FLAs for house and the dedicated starting battery for just this reason. I think many others do the same.

[skipmac]

Originally Posted by Bjorn_O

I will connect the capacitor to the solar panel with a resistor, with a value so that the leak current is not an issue. There are capacitors with a fairly low leak current that will not be discharged during the night. Supercapacitors have been tested in cars with good results. Having low internal resistance, they can deliver high currents and store enough energy for a couple of starts. They will also be recharged quickly. (I already have a jump start cable to use if the normal battery is empty.)

The advantages of capacitors you mention: very fast charging and the ability to delivery high currents make them extremely interesting. They also have a very high energy density, light weight, reliability and simplicity. However, keeping them charged and ready for use long term I still see as a serious problem.

What do you do when there's no recharge available from solar? I recall one sail in the Caribbean, years ago when I used celestial navigation, when I did not see the sun for two weeks.

I'm looking at an option for reliable engine starting without having to deal with frequent attention or additional complexity to my system.

With the current state of capacitor technology I don't see this as the solution for me but it could be right for you and your setup.