Lithium Charging Problems with DC to DC

[denis2000]

I thought it would be good to share our experience. This year we installed 2 x 100a lithium batteries. In order to protect the new 80ah alternator, in addition to a smart regulator, we decided to fit a dc to dc charger and a 60a starter battery as a slave. The idea of having a slave instead of using the boat’s starter battery was to make sure the latter wasn’t compromised. We also installed a decent monitoring system.

Through the year, charging times were increasing and discharging was getting quicker. I finally clocked the state of the slave battery - less than 10v! The dc to dc was supposed to stop taking a charge from the slave once it got down to 12.5v. That clearly wasn’t happening and, as a result, the slave battery was a gonner.

I have now changed the wiring so that the alternator charges the lithiums directly. They are getting back up to 100% much quicker than before. We will probably keep the set up as it is - much more simple. We feel that the alternator will be adequately protected by the smart charger and the lithiums have their own protection circuits.

Lesson - if you do have a dc to dc charger set up, make sure it does cut off to protect the battery it takes its charge from. I am so glad we decided to use a slave battery, as it would have been a fried starter battery!

Denis
Olivia Jane

 

[lw395]

Seems like a case of read, and understand, the manuals.
Since you don't identify the exact items you have, it's not clear whether the chargr was simply configured wrongly.
Neither is it clear that connecting the batteries directly to the alternator will be OK.
How can the alternator be protected by the smart charger?

When people talk of 100a batteries and 80ah alternators, it gives the impression that they know very little about electrics, or they are being lazy and not worrying about details.
I think you need to know what you are doing and care about the details with Lithium batteries.

 

[denis2000]

Thanks for your reply post - good points, well made. However of the three owners of our boat, I am the only non engineer, hence my inconsistency between amps and amp hours; forgive me! The owner with the most experience installed the system, following in-depth research and studying of the manuals. He guided me through the re-wiring, à system he had put in place so that we could go back to the simple set up if necessary. We took advice from the battery supplier before doing this.

The smart charger will (and does) stop the alternator from providing charge if it gets too hot. I understand that lithiums suck as much power as they can and have been known to fry alternators.

I don’t want to name the suppliers as we need to talk to the dc to dc people, as their product didn’t perform as it should.

Denis

 

[Ceirwan]

Thanks for your reply post - good points, well made. However of the three owners of our boat, I am the only non engineer, hence my inconsistency between amps and amp hours; forgive me! The owner with the most experience installed the system, following in-depth research and studying of the manuals. He guided me through the re-wiring, à system he had put in place so that we could go back to the simple set up if necessary. We took advice from the battery supplier before doing this.

The smart charger will (and does) stop the alternator from providing charge if it gets too hot. I understand that lithiums suck as much power as they can and have been known to fry alternators.

I don’t want to name the suppliers as we need to talk to the dc to dc people, as their product didn’t perform as it should.

Denis

The smart regulator if set up correctly should be able to reduce the output of the alternator to prevent it overheating as you say.

However, as the lithium batteries have their own protection systems, how have you protected the alternator from a high voltage cut off event?
If the BMS on the batteries decides that they're fully charged & shuts off your charging relay then the effect will be the same as if someone turned off the battery switch, you could damage your alternator and regulator.

 

[lw395]

The smart regulator if set up correctly should be able to reduce the output of the alternator to prevent it overheating as you say.

However, as the lithium batteries have their own protection systems, how have you protected the alternator from a high voltage cut off event?
If the BMS on the batteries decides that they're fully charged & shuts off your charging relay then the effect will be the same as if someone turned off the battery switch, you could damage your alternator and regulator.

All these things have solutions, but frankly, it's a waste of time discussing them with people who either don't understand the difference between an amp and an AmpHr, or can't be arsed to go beyond vague arm-waving descriptions of their alleged problems.

 

[denis2000]

All these things have solutions, but frankly, it's a waste of time discussing them with people who either don't understand the difference between an amp and an AmpHr, or can't be arsed to go beyond vague arm-waving descriptions of their alleged problems.

I was actually just sharing the experience we’ve had with a failed DC to DC unit resulting in a fried battery. I was not seeking advice and wasn’t “arm waving” and the problem certainly wasn’t “alleged”. But, hey-ho.

 

[denis2000]

However, as the lithium batteries have their own protection systems, how have you protected the alternator from a high voltage cut off event?
If the BMS on the batteries decides that they're fully charged & shuts off your charging relay then the effect will be the same as if someone turned off the battery switch, you could damage your alternator and regulator.

Thank you for this - we’ll have to make sure there’s effective protection.

 

[lw395]

I was actually just sharing the experience we’ve had with a failed DC to DC unit resulting in a fried battery. I was not seeking advice and wasn’t “arm waving” and the problem certainly wasn’t “alleged”. But, hey-ho.

But since you've declined to give any information about the items involved, or the configuration thereof, the value of what you're sharing is zero, or less.

 

[denis2000]

All these things have solutions, but frankly, it's a waste of time discussing them with people who either don't understand the difference between an amp and an AmpHr, or can't be arsed to go beyond vague arm-waving descriptions of their alleged problems.

I’m sorry that you think that it’s a waste of your time dealing with someone who isn’t an expert. If that’s the case, why did you bother posting a reply in the first place? Or are you just trying to demonstrate some “alleged” superiority?

 

[GHA]

I’m sorry that you think that it’s a waste of your time dealing with someone who isn’t an expert. If that’s the case, why did you bother posting a reply in the first place? Or are you just trying to demonstrate some “alleged” superiority?

In settings, top right, there's an option to ignore posts by the grumpy know-it-alls, means you don't waste your time having to read their posts. Speeds things up a lot. Most here are helpful and pleasant with a huge variety of knowledge & experience. Welcome to the forums :encouragement:

 

[gertha]

A thought or two.
If the smart regulator was linked to slave, as soon as engine on and volts up the lithium would draw from slave. Depending on engine revs the alternator may not have been producing as many amps as the lithium was drawing, although the apparent volts would be high as alternator on, so dc dc was doing its stuff, but draining slave.
Smart regulators can give problems, my own experience was batteries boiling after 24 hours of motering, this because of multiple small problems that only manifested them self when we run the engine for this long period.
I have no interest in high jacking the thread about my own problems, just to say smart regulators have to be treated with respect, they are only a little box that does as it is told.

Simon

 

[denis2000]

In settings, top right, there's an option to ignore posts by the grumpy know-it-alls, means you don't waste your time having to read their posts. Speeds things up a lot. Most here are helpful and pleasant with a huge variety of knowledge & experience. Welcome to the forums :encouragement:

Great, thanks. Done that!

 

[Ceirwan]

A thought or two.
If the smart regulator was linked to slave, as soon as engine on and volts up the lithium would draw from slave. Depending on engine revs the alternator may not have been producing as many amps as the lithium was drawing, although the apparent volts would be high as alternator on, so dc dc was doing its stuff, but draining slave.
Smart regulators can give problems, my own experience was batteries boiling after 24 hours of motering, this because of multiple small problems that only manifested them self when we run the engine for this long period.
I have no interest in high jacking the thread about my own problems, just to say smart regulators have to be treated with respect, they are only a little box that does as it is told.

Simon

Hi Simon,

If the alternator was unable to keep up with the current demand of the charging the lithium batteries then the voltage would drop. The regulator will try and maintain the voltage its set to, but if the charge acceptance of the batteries exceeds the current that can be delivered then it will be unable to maintain that voltage.

 

[gertha]

Ceirwan, Thanks for your input, what you have said make sense, my little brain was trying to think up a scenario where the dc dc would fail.

Simon