Keeping a start battery charged

[mitiempo]

Originally Posted by Frankly

Put the Odyssey in the car, getting out of Jacksonville might be more urgent than getting the anchor up.


Frankly

That's a good one.

[sailorboy1]

5 pages, who would have thought ?

[Wotname]

Originally Posted by a64pilot

So what do you guys think of a 1 amp battery tender? Automatic three stage charging wired in the the AC output of the generator, is on whenever the generator is, and off of course the rest of the time. Even at 1 amp it ought to be enough it keep it charged?
When I run the generator it’s usually only three or four hours and very infrequently now, I usually default to the Honda and run the Diesel once or so monthly.

I bought this Odyssey cause my kid said the Miata’s battery was dead, it wasn’t and I can’t return the Odyssey, so what to do with it?
Currently I use the house bank to start it, house bank is the only bank on my boat.

This started as more of a curiosity experiment than a real need

I think the small battery tender is the ideal solution for your proposed use. Cheap, simple, easy and will keep the Odyssey in tip top condition with a 100% SOC. You don't need anything more complicated or more expensive.

The only caveat is I haven't seen the specs of the intended battery tender but I am assuming it is similar to the ones I know which is last stage output voltage around 13.6V and a maximum output voltage of 1 amp.

[Wotname]

Originally Posted by mitiempo

...........

I,m not an innocent babe in the woods but a marine electrician.

Really, then perhaps you could answer my question posed back in post #46 which is copied below.

......... The Odyssey will be at 100% SOC (most of the time), why is it better to have it being charged for long periods at 14.somethingV when the manufacturer recommends 13.6V? ................

[Adelie]

Originally Posted by a64pilot

So what do you guys think of a 1 amp battery tender? Automatic three stage charging wired in the the AC output of the generator, is on whenever the generator is, and off of course the rest of the time. Even at 1 amp it ought to be enough it keep it charged?

When I run the generator it’s usually only three or four hours and very infrequently now, I usually default to the Honda and run the Diesel once or so monthly.



I bought this Odyssey cause my kid said the Miata’s battery was dead, it wasn’t and I can’t return the Odyssey, so what to do with it?

Currently I use the house bank to start it, house bank is the only bank on my boat.



This started as more of a curiosity experiment than a real need

That would work fine. Starter draw for even large engines is usually under 1Ahr so the tender should do fine.

[a64pilot]

Originally Posted by Wotname

I think the small battery tender is the ideal solution for your proposed use. Cheap, simple, easy and will keep the Odyssey in tip top condition with a 100% SOC. You don't need anything more complicated or more expensive.

The only caveat is I haven't seen the specs of the intended battery tender but I am assuming it is similar to the ones I know which is last stage output voltage around 13.6V and a maximum output voltage of 1 amp.

Specs are tough to find. I suppose it’s because it wouldn’t mean anything to most people. Sort of like desulphation chargers, many if not most believed they work.
Wouldn’t it be nice if they did?

Battery tender says float is between 13.3 and 13.5, but won’t tell you absorption voltage or I can’t find it if they do, I’ll try to send a message to see if they will answer.

[mitiempo]

Originally Posted by Wotname

Really, then perhaps you could answer my question posed back in post #46 which is copied below.

A fully charged battery will not accept more than an amp at bulk/absorption voltage. A charger ideally charges a battery to about 99% SOC before switching to float, which maintains. The charger should switches to float when the battery is accepting a very small amount of current, however many chargers use a timed absorption stage.

As I did post there are many thousands of start batteries that are wired to multi stage multi output chargers. When the start battery is full the charger often has many hours to go for the house bank to be fully charged. The start battery sees the same absorption voltage as the house bank for these hours and it does no harm.

Here is the link about ACRs I posted from Rod Collins:

https://marinehowto.com/automatic-charging-relays/

[Wotname]

Originally Posted by a64pilot

Specs are tough to find. I suppose it’s because it wouldn’t mean anything to most people. Sort of like desulphation chargers, many if not most believed they work.
Wouldn’t it be nice if they did?

Battery tender says float is between 13.3 and 13.5, but won’t tell you absorption voltage or I can’t find it if they do, I’ll try to send a message to see if they will answer.

On reflection, it probably doesn't matter what the last stage set point is as long as it between 13.3V and (say) 14.5V as in your case, it will only be operational while the generator is running and not charging the battery 24/7.

At least you needn't worry about self discharge and sulphating issues with the Odyssey as they have excellent open circuit storage ability (assuming 100%SOC).

[Wotname]

Originally Posted by mitiempo

........

As I did post there are many thousands of start batteries that are wired to multi stage multi output chargers. When the start battery is full the charger often has many hours to go for the house bank to be fully charged.The start battery sees the same absorption voltage as the house bank for these hours and it does no harm.

.............

In your opinion or have you done empirical testing as this is simply not supported by the battery manufacturer.

I agree that it is a storm in a tea cup for most and if the start battery is low cost, the shorter life is immaterial. As pertaining to this thread though, I repeat that Odyssey batteries do not fall into the low cost cheap and cheerful category (at least not is Oz, the USA may be different).

[Wotname]

Originally Posted by mitiempo

.....

Here is the link about ACRs I posted from Rod Collins:

https://marinehowto.com/automatic-charging-relays/

I have read this article several times over the years and I am in general agreement with most of it.

Like another poster upthread, I think he doesn't really address the potential to overcharge a start battery. He glosses over the issue.

And stated upthread by myself and others, it isn't a big issue if the start battery is low cost but there is no way to describe as best practice if the house charging setup is operating at absorption levels most of the day.

Second best is OK if you realise it for what it is.

[Simi 60]

Our Victron inverter charger which is on 24/7/365 has a trickle charge port off of it for starts

We also have a victron VSR that gives full charge to starts when engine is running then switches automatically to house bank and pumps them up.
Great bit of kit for $50.

[valhalla360]

Originally Posted by a64pilot

Any idea that you harming your house bank by using it to crank the engine on an average sail boat is silly and uninformed.
However if you want a battery just to start an engine, your better served with a smaller and lighter and less expensive starter battery, but there is no logical reason at all that a house bank can’t start an average sized sailboat engine with no sweat probably capable of doing it 100 times or more.

What I really cant understand is all these posts or what will I do when I kill my house bank by accident, do some of you really do that? Am I the only person who looks at my voltage and SOC first thing in the morning and again in the afternoon? Am I the only person who has a low voltage alarm?

I guess my answer to them is you will do the same thing when you accidentally run out of fuel, because that’s all a battery bank is, an energy supply, like your fuel tank, except I can refuel my battery bank at sea, I cannot my fuel tank, well actually I can but that’s another argument.

Agreed. No issue using the house battery bank to start. Also, if it's good size and in decent condition, I wouldn't expect any major voltage issues. Most marine electronics are fine with a pretty wide range of voltage.

If you are worried about a dead battery bank, simpler and cheaper to buy a jump box and put it on the maintenance task list to charge every couple weeks.

We had an even better solution...if the battery is dead, just pull start. Of course, we had an outboard.

I believe a lot of older diesels, you can add a manual start if it's a big concern for you. Not fun but should be a rare event. I would expect the people on this thread spending so much time and effort building the ultimate battery bank are also doing maintenance and really watching the condition, so they are even less likely to have a dead house battery bank.

[valhalla360]

Originally Posted by wingssail

OK I'll give you two examples:

1. You have been at sea for a few days, sailing continuously, and the extra amperage that is required to run the ship at night is running down the house batteries. You know this by the battery voltage or other monitors, or by a low voltage alarm, but it's midnight and you don't want to start a charging cycle at that time (for whatever reason). You want to wait until the scheduled cycle in the morning. But morning comes and the house batteries are too low. You switch to the start battery and Bob's your uncle.

2. You leave you refer and freezer full of food and the refer system running, on shore power, when you leave the boat for a couple of days. There is insufficient sun or inadequate solar power to keep the batteries up, but shore power does that, until the cord gets unplugged. You come back and the batteries are dead, (plus, the food is rotten. You switch to the start battery and Bob's your uncle (except for the rotten food).

1. You purposely put yourself into the situation if you hear the alarm and ignore it. You can't fix stupid.

2. If the shorepower came unplugged, plug it in and the battery charger will charge it. I'm probably going to put off the day sail for a bit to clean the rotten food out of fridge anyway. Plus I would want to make sure the bank is taking a good charge after the abuse before trusting it will take a charge while motoring.

[wingssail]

Originally Posted by valhalla360

1. You purposely put yourself into the situation if you hear the alarm and ignore it. You can't fix stupid.

2. If the shorepower came unplugged, plug it in and the battery charger will charge it. I'm probably going to put off the day sail for a bit to clean the rotten food out of fridge anyway. Plus I would want to make sure the bank is taking a good charge after the abuse before trusting it will take a charge while motoring.

Ignoring a low battery situation overnight while sailing may seem stupid to you but to me it is taking a calculated risk, (and not much of one when you have a starting battery sitting there ready). The justification for doing so could be as simple as: not wanting to disturb the sleep of the off watch. I think it is stupid not to be able see that there could be valid reasons to do that.

And in the case where shore power plug came un-plugged, a starting battery might be useful if you need to start the engine immediately upon returning to find the house dead (even before the charger has built up sufficient charge to get the engine going).

The previous question had been "how could anyone let their house battery run down?" or something to that effect.

There are lots of ways in which it is possible. I gave a couple. I'm not sure why you responded they way you did. Do you think these are not possible or that there are not others?

[valhalla360]

Originally Posted by wingssail

Ignoring a low battery situation overnight while sailing may seem stupid to you but to me it is taking a calculated risk, (and not much of one when you have a starting battery sitting there ready). The justification for doing so could be as simple as: not wanting to disturb the sleep of the off watch. I think it is stupid not to be able see that there could be valid reasons to do that.

And in the case where shore power plug came un-plugged, a starting battery might be useful if you need to start the engine immediately upon returning to find the house dead (even before the charger has built up sufficient charge to get the engine going).

The previous question had been "how could anyone let their house battery run down?" or something to that effect.

There are lots of ways in which it is possible. I gave a couple. I'm not sure why you responded they way you did. Do you think these are not possible or that there are not others?

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.