Keeping a start battery charged

[Emmalina]

10R resistor and a silicon diode between the house and start has worked fine for me for the last 10 years !

[Stu Jackson]

Overcharging with Combiners or ACRs The MYTH:
http://c34.org/bbs/index.php/topic,7052.0.html

[a64pilot]

Originally Posted by Stu Jackson

Overcharging with Combiners or ACRs The MYTH:
http://c34.org/bbs/index.php/topic,7052.0.html

If you accept that, then all you need is charge sources that output absorption voltage, none of the three stage nonsense, yet we all seem to live and die by three stage charging, not just set voltage to absorption and leave it there.

I have however wondered how bad it would be on a start battery, standard automotive voltage is 14V +or- .2, so 14.3 is only .1 above standard automotive voltage, add in the length of wire that I woud have and I’m sure I would be closer to 14V

[wingssail]

Originally Posted by a64pilot

I’m pretty much going to do that with the two banks, except connect everything to bank #1 which will be the one in use, leaving one usually unused charger to bank #2 to keep it topped off every once in a while.

But that leaves the start battery, it will undergo absorption voltage every day until the bank is at 2.2 amps acceptance, which of course includes it as the ACR will have combined the two, that’s unacceptable, that will eventually surely dry out the electrolyte.

I’ve just about decided that from a financial perspective and ease of use etc that an inexpensive battery minder connected to it is the best way, then when the generator is running, the battery minder is powered, and they go to float or turn off when the battery is fully charged, just they are tiny little chargers, but that’s all a small Odyssey battery would need that is only used to start a one cylinder Kubota anyway. Generator run time is never over a coupe of hours anyway.

But yes if I ever do kill both banks, I have a Honda that can power a 100 amp charger, and with a start battery my generator can power both chargers for a 185 amp total, that would start the engine and add theoretically another 165 amps.

Without a battery failure I don’t understand how you could kill a bank on a boat thats being used. As a matter of course I check the bank in the morning and in the afternoon.

Sorry a64pilot, that is not the solution I recommend, and it defeats the purpose.

OK, set aside the fact that you have two house banks for a second.

Hook the main house bank to pos 1 on the switch.
Hook the start battery to pos2 on the switch.
Connect ALL charging sources to the HOUSE side of the switch.
Take the ACR to the next swap meet.

Now, you will NEVER be charging the start battery unless you switch to it on purpose. That solves your worry about over charging or evaporating the battery dry.

You can charge either battery, start on either battery, and run the house on either battery. It's all under your control. You can even combine them with "Both" and you can switch everything "OFF" in an emergency.

As for the second bank of house batteries, since they are different types of batteries, you might not want to charge them together, so you could use the ACR on them, or put a second Off-1-2-Both switch so you can choose which house battery bank is actually connected when your main switch is on position #1.

Would you like me to do a diagram?

[Wotname]

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?
.................
It would seem that a trickle charger would be better and not the ACR?

You could just keep the Odyssey as an emergency battery that is disconnected until you need it. Odyssey say their batteries have a very very low self discharge rate and they are good for a 2 year storage life between charges. I wouldn't leave one for 2 years but I am happy to leave my Odyssey open circuit for 6 months (more or less). There is no requirement to keep it at float voltage day in day out.

If you do use it for the generator start battery, maybe you could rig up a relay which is operated by the generator output so whatever charging source is used is only connected while the generator is running. This would depend somewhat on your generator usage and may not be suitable if the generator is only used for short infrequent durations.

[BlackHeron]

Wire the ACR to BSS specs with alternator charge to start battery side. Might as well use the same wire for alternator and starter. When start battery gets to 13.3v it'll combine and drop the house bank into the load. It won't overcharge as long as start battery and house battery banks are all the same chemistry. Wire the solar and wind turbine into the house battery side. The ACR will not combine until again the charge voltage gets to 13.3v. No worry about overcharging with like chemistry. That's the key. If different chemistry then charge control will need to be different. Nigel goes into this in his books. If this is a generator then only charge to full and only equalize to a schedule and keep the start battery to the same schedule. Schedule depends on the chemistry. Different chemistry between banks and everything gets extremely complicated without really smart automatic switching.

We have simple, easy, and cheap FLA everywhere and use the BSS ACR and their simple Isolation switch that keeps engine and house switching separate letting the basic ACR do all of the thinking.

Untrained crew can't screw up the diodes in your alternators since the switches need never be touched normally other than occasionally from On to Off when the boat is left for extended periods or back again (simply turn back to On when you get back and put the boat back into service)

We never turn ours off since the anchor light is on the house panel and don't leave the boat more than a few hours at a time anyhow -althoufh occasionally after dark. We just keep the anchor light on 24/7 on the hook since it only draws 2W and is a nothing load in the big picture. Photocells fail, better savmfe than sorry. We've never needed to combine manually as after 3 years we've never had an issue and neither bank has ever gone below 50% charge. In fact the starter battery only gets discharged enough to start the engine and is immediately charged back up to at least 13.3v before the house bank is tied in automatically when the engine is running. We usually hit equalization charge on every sunny day unless it has been a few days of overcast days with no wind. We have never had to run the engine to charge and have sat at anchor or a mooring ball for months at a time

[Calif.Ted]

A trickle charger powered by the generator and connected to the start battery? kind of a shade tree mechanic's alternator replacement, simple if nothing else. Seems like a couple amps for the time the gen runs would be more than ample.

[a64pilot]

Originally Posted by wingssail

Sorry a64pilot, that is not the solution I recommend, and it defeats the purpose.

OK, set aside the fact that you have two house banks for a second.

Hook the main house bank to pos 1 on the switch.
Hook the start battery to pos2 on the switch.
Connect ALL charging sources to the HOUSE side of the switch.
Take the ACR to the next swap meet.

Now, you will NEVER be charging the start battery unless you switch to it on purpose. That solves your worry about over charging or evaporating the battery dry.

You can charge either battery, start on either battery, and run the house on either battery. It's all under your control. You can even combine them with "Both" and you can switch everything "OFF" in an emergency.

As for the second bank of house batteries, since they are different types of batteries, you might not want to charge them together, so you could use the ACR on them, or put a second Off-1-2-Both switch so you can choose which house battery bank is actually connected when your main switch is on position #1.

Would you like me to do a diagram?

No I understand exactly what your saying but what your saying is to charge the generator start battery also means charging the unused secondary bank, again putting the bank through an absorption phase when it’s fully charged to begin with.

[a64pilot]

Originally Posted by Calif.Ted

A trickle charger powered by the generator and connected to the start battery? kind of a shade tree mechanic's alternator replacement, simple if nothing else. Seems like a couple amps for the time the gen runs would be more than ample.

Most battery tenders are .75 to 1 amp and are three phase, just current limited bulk at less than an amp is truly a trickle.
I think a start due to its very short duration reduces the charge on a battery only slightly and it’s hard to replace that energy, doesn’t take much amperage.

[a64pilot]

Originally Posted by BlackHeron

Wire the ACR to BSS specs with alternator charge to start battery side. Might as well use the same wire for alternator and starter. When start battery gets to 13.3v it'll combine and drop the house bank into the load. It won't overcharge as long as start battery and house battery banks are all the same chemistry. Wire the solar and wind turbine into the house battery side. The ACR will not combine until again the charge voltage gets to 13.3v. No worry about overcharging with like chemistry. That's the key. If different chemistry then charge control will need to be different. Nigel goes into this in his books. If this is a generator then only charge to full and only equalize to a schedule and keep the start battery to the same schedule. Schedule depends on the chemistry. Different chemistry between banks and everything gets extremely complicated without really smart automatic switching.

We have simple, easy, and cheap FLA everywhere and use the BSS ACR and their simple Isolation switch that keeps engine and house switching separate letting the basic ACR do all of the thinking.

Untrained crew can't screw up the diodes in your alternators since the switches need never be touched normally other than occasionally from On to Off when the boat is left for extended periods or back again (simply turn back to On when you get back and put the boat back into service)

We never turn ours off since the anchor light is on the house panel and don't leave the boat more than a few hours at a time anyhow -althoufh occasionally after dark. We just keep the anchor light on 24/7 on the hook since it only draws 2W and is a nothing load in the big picture. Photocells fail, better savmfe than sorry. We've never needed to combine manually as after 3 years we've never had an issue and neither bank has ever gone below 50% charge. In fact the starter battery only gets discharged enough to start the engine and is immediately charged back up to at least 13.3v before the house bank is tied in automatically when the engine is running. We usually hit equalization charge on every sunny day unless it has been a few days of overcast days with no wind. We have never had to run the engine to charge and have sat at anchor or a mooring ball for months at a time

This is a generator with no alternator.
Everyone thinks you can’t overcharge as long as banks chemistry is the same, is incorrect. The reason it’s incorrect is the the start battery will get to 100% SOC quickly because it was at 95% or better to start with, the house bank will take on average 6 hours at absorption voltage if it was at or close or 50% SOC.
So the start battery will be at absorption for an extra 5 hours so so, and every single day even when it didn’t start the generator and is at absolutely 100%, it’s going through another full absorption charge, every day from Solar.

You either have to accept that it’s being overcharged, or accept that all we need on our Solar chargers is one voltage set point, absorption.

[a64pilot]

I’ll probably install it with the ACR and put the ACR ground on a switch and only turn it on when the generator is running, may even get slick and use an automotive relay so that it’s switched on automatically, use the generator blower circuit to power the automotive relay.
That way the battery will only be charged when the generator is running, which accomplishes the same thing as the battery tender, just with more cabling.
So maybe back to the battery tender?

[BlackHeron]

Charging a battery is not like filling up a glass of water. Charge current is driven by voltage and resistance. With the larger more-discharged house bank dropping circuit voltage down to bulk or acceptance charge levels the voltage will never get to.levels where it can ever push the start battery into equalization, its internal resistance simply will not allow it to offgas or overcharge until voltages get higher. This is basic DC series/parallel theory.

[Warby12]

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?

If it is the Blue Seas ACR you are talking about, it doesn't combine the banks until voltage reaches 13.6 volts for 30 seconds or 13volts for 2 minutes, so it won't drag the start batteries voltage down below fully charged.

As far as overcharging, I have wondered the same myself... We have a 500AH AGM house bank and an AGM start battery that we never use (Came like that). We use the house bank for starting. The backup starter is just there to be hooked up for emergencies. Of course it cops the full bulk voltage everyday (via the ACR) from charging the house bank. Lately its overnight voltage has been dropping down to 12.6 so I think it's dying but it came with the boat so is well over 6 years old. Did the bulk charging do this? Maybe.
Having said that, I am going to remove it and just keep the house bank for everything including starting. Then we can dump the ACR and remove a bunch of wiring. I love any change that simplifies.

We have a Victron battery monitor with a low voltage alarm set to 12.3V so cannot exhaust the house bank enough to prevent starting. Also the Victron has facility for mid point monitoring which I can hook up to help to detect a sudden single battery failure. If all else fails we can separate the good batteries and let the solar charge.




.

[ranger58sb]

Originally Posted by a64pilot

So how do people keep their start batteries charged,

I put an Odyssey 34M-PC1500 battery on our genset, disconnected that battery from the charger, and just let the generator engine's (Yanmar 3TNE74) alternator charge the battery.

I never saw enough self-discharge to ever have to care about it... even a couple times over winter months here on the hard.

It was installed in mid-2009, and replaced it with a new one when we were down in Ortega last winter while I was trying to troubleshoot a "generator won't start" problem. The battery was just then beginning to test a bit low, but it turned out the real problem was just the battery switch, not the battery itself. IOW, the battery lasted for at least 11 seasons and I probably could have gotten one more out of it.

Edit: Ah. I posted too early, didn't realize your on about a generator with no alternator. The reason I took the battery off of our main 3-bank charger in the first place is because it seemed to be being overcharged. Inordinate amount of venting. I think because it was so small in comparison to the other two main banks.

-Chris

[mitiempo]

Originally Posted by a64pilot

This is a generator with no alternator.
Everyone thinks you can’t overcharge as long as banks chemistry is the same, is incorrect.

You either have to accept that it’s being overcharged, or accept that all we need on our Solar chargers is one voltage set point, absorption.

The start battery will not overcharge. As long as the voltage is not over the recommended bulk voltage for the battery - typically 14.4 - there is no problem. The battery and its internal resistance determines how much current it accepts, regardless of the amount of current. The only way to get a battery that is fully charged to accept more current is to raise the voltage.

If ACRs were damaging to start batteries we would have heard about it by now - there are millions in use.

There are also millions of cars on the road with alternators set at 14.4 volts and their start batteries are constantly exposed to this. It has no effect on battery life.

Also another point if using an ACR the charge sources should go to the larger of the banks. If they go to the start battery there will be chattering as the ACR cycles on and off. This is explained by Blue Seas in their literature.