Keeping a start battery charged

[rslifkin]

To me, engine starting power is safety-critical. Yeah, if all is going even remotely well, the house bank should have plenty of juice to start an engine. But when it's 4 am, the house bank is down to 50% and you need to get an engine running and move the boat in the dark "right now" is not the time to want to think twice about it or have the voltage dip from starting the engine with a partially charged house bank cause an electronics reboot when you really needed that plotter / radar working and it was already in standby with the screen off, ready to wake in a few seconds rather than waiting for a full startup.

It's one of those Murphy's law things. The only time you'd have a shortage of starting power is at the worst possible time. It's easy enough to provide / maintain a protected source of starting power, keeping the house as backup. And if the system is well thought out, it shouldn't require any extra effort / switching to use it.

[a64pilot]

I think our way of thinking is what’s different, my bank unless it’s shorted out or something will never be even remotely close 50% at 4AM, more like greater than 80%, but even at 50% it will start my little motor, and almost certainly would even at 20% which on my bank is 11.6V, probably would even much lower. Why? Because the voltage drop on 300 lbs or greater of batteries is quite small when hit with a 200 amp load as compared to the voltage drop of one 30 lb starter battery.

Besides my low voltage alarm is going off at around 50% anyway. So how did I get lower?

OK, so I lost a battery due to an internal short and it’s discharging the rest, it happens, even to the best of us and the best batteries are not immune, that’s why my bank is separated into two, deselect the bank with the bad battery until you get around to wiring around it later. In my case as I’m 6V, I’ll lose two batteries, not just one, so I go from 660 AH to 440.

But you should still be able to start the engine.

Worst, worst case I crank my generator, I have 185 amps of shore chargers, I bet those by themselves would start the propulsion motor.

[wingssail]

Originally Posted by valhalla360

You are creating convoluted unrealistic scenarios to justify doing silly things.

Sure, people COULD do these things but they would be poor decisions. Designing to mitigate for the ultimate idiot is a losing proposition.

So, just to be clear, your view is that either of the two scenarios I described are unrealistic and convoluted and would only be done by the "ultimate idiot" and that installing a starting battery is a silly thing?

OK, I gotcha.

[wingssail]

Originally Posted by a64pilot

I think our way of thinking is what’s different, my bank unless it’s shorted out or something will never be even remotely close 50% at 4AM, more like greater than 80%, but even at 50% it will start my little motor, and almost certainly would even at 20% which on my bank is 11.6V, probably would even much lower. Why? Because the voltage drop on 300 lbs or greater of batteries is quite small when hit with a 200 amp load as compared to the voltage drop of one 30 lb starter battery.

Besides my low voltage alarm is going off at around 50% anyway. So how did I get lower?

OK, so I lost a battery due to an internal short and it’s discharging the rest, it happens, even to the best of us and the best batteries are not immune, that’s why my bank is separated into two, deselect the bank with the bad battery until you get around to wiring around it later. In my case as I’m 6V, I’ll lose two batteries, not just one, so I go from 660 AH to 440.

But you should still be able to start the engine.

Worst, worst case I crank my generator, I have 185 amps of shore chargers, I bet those by themselves would start the propulsion motor.

It occurs to me, A64pilot, that with your two battery banks on the house side, you have a starting battery, just a big one. Many of us had equally sized banks #1 and #2 for years. But carrying around a bunch of heavy batteries which are usually unused, was wasteful so we changes to a smaller starting battery, and endeavor to keep it charged, not over charged.

And in the scenario you described (a short in a battery) will discharge both banks if paralleled.

[Thumbs Up]

Install one of these: https://www.defender.com/pdf/259019_Magnum.pdf

[a64pilot]

Originally Posted by wingssail

It occurs to me, A64pilot, that with your two battery banks on the house side, you have a starting battery, just a big one. Many of us had equally sized banks #1 and #2 for years. But carrying around a bunch of heavy batteries which are usually unused, was wasteful so we changes to a smaller starting battery, and endeavor to keep it charged, not over charged.

And in the scenario you described (a short in a battery) will discharge both banks if paralleled.

I have two banks, a 220 AH and a 440AH. I have them ganged together with the battery selector switch set to All. You could argue they are both start banks because they can both be used to start the engine or the generator.
The alternator charges whichever bank is selected, the Solar charges the little bank, the inverter charges the larger and the Sterling charges both. But ganged together everything charges it all of course.
Yes if left connected one shorted battery would eventually kill both, however it would take time, the low voltage alarm will go off, and you’ll investigate, and hopefully feeling a hot battery, you will isolate the bad bank with the battery selector, and physically disconnect the bad battery. The other bank still have enough juice to start the motor or generator, and when disconnected from it’s heavy load, will recover voltage pretty quickly, but either way, start something to recharge the remaining good bank, the generator would be best as it’s a larger charge source and burns less fuel, and is designed to supply electrical power.

Only reason why I’m considering a generator start battery is I happen to have this brand new $150 battery sitting here, and I guess I’m bored, but I don’t think it’s actually necessary.

I also happen to have a Blue Seas ACR that would seem to be perfect for the job, but as I thought about it, it seemed that subjecting a fully charged batter to a charge profile every day, day after day wouldn’t be good for it, so I though I’d ask others how do they keep their start battery charged.

From the answers I got, it would seem to indicate that automotive start batteries, which is what I assume most use are very tolerant of overcharging.

Which now has me wondering why. Are all lead acid batteries tolerant of overcharging and we have bought into three stage charging, when it’s not really necessary?

Or is it just start batteries are more tolerant?

Or is it any LA battery will tolerate 5 or 6 hours of absorption a day, just don’t float them there 24/7?

[valhalla360]

Originally Posted by wingssail

So, just to be clear, your view is that either of the two scenarios I described are unrealistic and convoluted and would only be done by the "ultimate idiot" and that installing a starting battery is a silly thing?

OK, I gotcha.

Wasn't calling you an idiot...there is a design principal that you can't design for the ultimate idiot because idiots are too good at finding new and inventive ways to break things.

I'm sure people do ignore low voltage alarms. I see people doing stupid things all the time. I'm sure some people will wonder what that dang buzzer is and start turning off switches till it goes away never knowing what it really was.

I just can't see someone so concerned about not being able to start the boat that they install a low voltage alarm and then ignore it when it goes off.

[wingssail]

Originally Posted by valhalla360

Wasn't calling you an idiot...there is a design principal that you can't design for the ultimate idiot because idiots are too good at finding new and inventive ways to break things.

I'm sure people do ignore low voltage alarms. I see people doing stupid things all the time. I'm sure some people will wonder what that dang buzzer is and start turning off switches till it goes away never knowing what it really was.

I just can't see someone so concerned about not being able to start the boat that they install a low voltage alarm and then ignore it when it goes off.

So you do see the difference between blindly ignoring a low voltage alarm and deciding that recharging that battery could safely wait until morning, for the reason I gave? Especially since there is a starting battery there waiting to be used, and anyhow experience has told us that the house battery will still start the engine after another four hours, even if it is low enough to trigger the alarm, don't you?

And I am pretty sure that everyone who sails on long passages, including several nights at sea, racers or cruisers, will have experienced the overnight draining of the house battery bank. This is not a contrived or convoluted situation, although those who have not done ocean crossings under sail, or always use the engine while cruising, might not have experienced it.

There are a lot of reasons to have a low voltage alarm besides fear of not being able to start the engine; that is low on the list of worries because we do have a starting battery sitting there waiting.

"...you can't design for the ultimate idiot...". Yeah I understand that, I've been a designer all my life, however I believe that if you follow the 80/20 rule you can stop a lot of them with a little effort, and I don't believe in using that principle as an excuse for not trying to design a redundant system, even if is is not going to be "fool proof".

[Marathon1150]

Originally Posted by steamgoat

Echo charger, trickles it off the main bank when main bank is charged adequately , Has worked perfect for last 7 years.

We also do this, on two boats because it has worked so well on one boat over the past 12 years. On both boats, the start battery is isolated from the house bank and receives a charge via a Xantrex echo charger if there is power to spare.

On boat #2, the engine has two alternators (a PO did this - I wouldn't). The small original alternator engine alternator only charges the start battery. The big (160A) alternator charges the house bank. The solar panels only charge the house bank. The battery switch has three positions: off, house bank and "emergency" which combines the house bank with the start battery. I have had to use this only once in 12 years on the first boat. So far never on boat #2.

The OP does raise an interesting question however. I have never questioned the wisdom of having a start battery and a house bank. I'm now wondering why a start battery is needed at all, as did a64, the OP.

[valhalla360]

Originally Posted by wingssail

So you do see the difference between blindly ignoring a low voltage alarm and deciding that recharging that battery could safely wait until morning, for the reason I gave? Especially since there is a starting battery there waiting to be used, and anyhow experience has told us that the house battery will still start the engine after another four hours, even if it is low enough to trigger the alarm, don't you?

If you really do assess the system and determine it can wait until morning, you will be able to start the engine in the morning and it's not a valid example.

Unless you are in some emergency situation, desperate not to run the motor, the stress of worrying if it will start in the morning, isn't worth it, just start the motor. I'd much rather be woken off watch by you saying you are charging the battery bank (awake for a few seconds then roll over and back to sleep) rather than hearing the "wa wa waaaa....." of a dying starter (then I'm thinking what the @%@#% am I going to have to fix now).

[noelex 77]

Originally Posted by a64pilot

From the answers I got, it would seem to indicate that automotive start batteries, which is what I assume most use are very tolerant of overcharging.

Which now has me wondering why. Are all lead acid batteries tolerant of overcharging and we have bought into three stage charging, when it’s not really necessary?

Or is it just start batteries are more tolerant?

Start batteries have an easy life compared to house batteries. The are typically only discharged a few percent and then very rapidly charged up 100%. Ideal conditions for a lead acid battery.

They should last a very long time, but often only have a short life. This is due to a combination of factors mostly related to poor charging practices. Many are charged directly from a single stage engine alternator with typically low charging voltage. Others are charged via a VSR with excessively long absorption times.

As they are generally cheap and easily replaced batteries, this short lifespan is acceptable. A KISS approach for the start battery, without a sophisticated charge algorithm and the associated equipment makes a great deal of sense for many installations. If you do want to install more complex charge control, the start battery can be made to last much longer.

Personally, I have a very simple charging system for my start battery. The house and start battery are completely independent systems. The start battery is charged by its own (dumb) engine alternator and nothing else. The charge profile is not ideal and the start battery will have a shorter life as a result. On the other hand, it is a very simple system with little to go wrong and few failure points.

[a64pilot]

Automobiles, which I assume is what a start battery is essentially, and it lives a life pretty similar to an automobile, a continuous voltage of 14 plus or mins .2V.
Above float for most batteries, but below absorption for most. However starting the average car surprisingly takes less than 1 AH, even for a big V8, it’s very high current, but on average less than 2 sec.
So it doesn’t take much at all to return one to full charge, and it’s going going to be a very low current as the battery will only accept a trickle when it’s almost completely charged.
Personally I like the two alternator approach with one being a regular automotive alternator. I’d also want to be able to connect my start and house banks together, that would give me some redundancy if my fancy high power three stage alt kicks the bucket, charging the house bank at 14V is slow, and less than ideal, but at least your charging.

I think I’m going with a 2 amp battery tender, 2 amps is plenty to fully recharge in a couple of hours, I bet it won’t accept an amp anyway. I was going to wire it to the house AC, so that whenever there is AC, it’s charging, but as I often turn the inverter on for just a couple of minutes for us to vacuum, run the toaster or the vacuum sealer of whatever I decided not to, so I’ll just wire it to the generator side of the transfer switch, because I almost never start the generator and not let it run for at least an hour min.

Found a nice battery box specifically for it for about $20.
https://www.portablepower.com/produc...ttery-box-unf/

This battery maintainer
https://www.amazon.com/NOCO-GENIUS2D...%2C181&sr=1-22

[CharlieJ]

117 posts!

Let's talk about guns onboard;-)

[mcon12000]

My start battery is charged by the house bank via a victron DC to DC charger. This allows my alternator to always be connected via its external regulator to the house bank and the charge profile for the house will not damage the start battery. I no longer have a 1-2-all switch I just have an on/off switch for the DC panel.

The victron or any other Quality DC-DC charger will allow you to maintain a AGM battery with a Lithium or Gel Bank as an example. So the inverter charger, alternator and solar are all charging the house bank and the Victron charges the start battery only.

I have a Braille Battery for starting only its 7”x 8” or so and weighs next to nothing they’re used in race cars to save space. Worth checking out if you’re out of space or want to reclaim some.

Remember to fuse and connect everything with the appropriate wire awg since any voltage drops that aren’t compensated for by the charger are the same as having the wrong charge profile.

[Happ]

Originally Posted by a64pilot

I have never used a start battery as I don’t see the logic in one, but have now gotten a new Odyssey battery I need to find a use for and was thinking maybe use it as a generator start battery, generator doesn’t have its own alternator, I have a Blue Seas ACR in spares and it would be simple to just use it.
But here is the problem as I see it, with the ACR you would be subjecting the little Odyssey to a full absorption charge every day, with it already at 100% SOC and over time, surely that will kill it.
So how do people keep their start batteries charged, if by using an ACR, it’s going to kill it by overcharging it every day, day in and day out?

Along the same lines, I will soon have a new bank, but will keep most of the old bank for redundancy, but don’t plan on using it. I am going to isolate it with the battery switch and just use my little shorepower charger that can charge two independent banks once a month or so to keep it fully charged.
All my charging is done usually by my inverter / charger and Solar, and I wasn’t going to connect them to the back up bank.

But the ACR seems to be a flawed concept, does it not?
If at the beginning of the day, my big bank is at 12.5 V as it’s discharged, but the starter bank is at 13V cause it’s fully charged,won’t you first discharge it when the two banks combine, then overcharge it when the voltage gets back to absorption?
It would seem that a trickle charger would be better and not the ACR?

Simple answer to why you have a dedicated start battery is the battery type should be different. Your house batteries are typically Deep Cycle. They are for slow drain. A start battery has a high initial output to start the engine but drains quickly. For instance when your car doesn’t start you can see the power in the battery weaken very quickly.

Charging the batteries can be done through Controllers and through shore power battery chargers. Alternators are often enough to keep your start battery charged. Just like in a car.