Battery Charger -> House -> DC/DC Charger -> Lithium?

[mikeboatboy]

I've upgraded the house bank on my boat to Lithium, 35 amp alternator charges the AGM start bank, which then charges the Lithium via a Victron 12/12/18 DC/DC charger. All good there.

Question is, my shore-power battery charger is designed for lead acid/agm and connected to the AGM start bank, and it's a 5-amp charger. Once the AGM is charged, will it be OK to use the DC/DC charger to use the "overflow" energy to pass along to the Lithium battery? Or should I buy another shore-power charger specifically for Lithium,

Or am I misunderstanding something. My hope is once the AGM is charged sufficiently, the DC/DC charger will start requesting power to charge the Lithium and that power will be provided.

With the 5-amp shore-power charger, and the 18-amp DC/DC charger, I can see the Lithium depleting the AGM fairly fast because the 5-amp shore-power charger won't be able to keep up. The DC/DC charger will shut down, let the AGM top up again, then turn on again, over and over until the Lithium is fully charged.

Trying to keep things simple and not have to buy more stuff if I don't have to. Another idea I had was to buy a 30-amp shore-power charger that would be able to keep up with the DC/DC 18 amp charger.

Any ideas? Or should I just have two shore-power chargers, one for each bank.

 

[Samsonite801]

If it were me, I'd probably either get the separate LFP charger (like you had mentioned above), since the LFP have a different chemistry. Or get a bigger shore charger for the AGM bank that can supply enough input amps to charge the AGM and meet the additional demand from the DC-DC Victron charger to run while plugged into shore power (although maybe more loss that way).

 

[mikeboatboy]

Thanks for your input Samsonite. Pardon my lack of understanding of electricity. If I went with the option to buy a larger 30-amp shore charger, connect that into the AGM start battery, and allow the DC/DC charger to detect when the start battery had reached a certain voltage before kicking on, the extra amps flowing through the AGM battery and onto the DC/DC charger will not affect the way in which the AGM is maintained by the shore charger?

This is my favorite solution as I have very limited space to mount equipment.

 

[Samsonite801]

Thanks for your input Samsonite. Pardon my lack of understanding of electricity. If I went with the option to buy a larger 30-amp shore charger, connect that into the AGM start battery, and allow the DC/DC charger to detect when the start battery had reached a certain voltage before kicking on, the extra amps flowing through the AGM battery and onto the DC/DC charger will not affect the way in which the AGM is maintained by the shore charger?

This is my favorite solution as I have very limited space to mount equipment.

No, once the AGM is charged, it will just be sitting in float, and the juice is just spilling off the top from charger to the other DC-DC charger... The AGM is just like a water tank, just sitting there full, and the power is skimming along over the top supplying the Victron charger.

 

[mikeboatboy]

That makes sense to me, great analogy. I think I'll go this route. Thanks very much Samsonite.

 

[deeuubee]

Once your AGM battery is full from the shore charger, it basically turns down to a trickle charger until your AGM voltage drops low enough to engage charge mode again. There's not much to pass along. Plus you're only going to get a max 5 amp to the DC-DC charger at full output anyway.

Just replace your shore charger with a smart charger and connect it as needed.

Smart Charger

edit: not endorsing that charger, just that those type are available.

 

[Goboatingnow]

No, once the AGM is charged, it will just be sitting in float, and the juice is just spilling off the top from charger to the other DC-DC charger... The AGM is just like a water tank, just sitting there full, and the power is skimming along over the top supplying the Victron charger.

That’s not what happens. In order to trigger the dc dc , you will need to set a high enough setpoint on your dc dc. But your mains charger will be in float mode at around 13.6-13.8 hence your dc dc will not switch on.

Hence you will need to set the dc dc set point lower resulting in overcharging the AGMs. ( which they actually don’t like ).

Charging a lithium source from an AGM which is simultaneously being fed by a dc charge source ( alternator solar or mains charger ) is just a bad idea. It will result the lead acid chemistry being charged incorrectly

A proper Li system has all charge sources including the alternator compatible with and connected to the Li bank on the basis this is the bank being cycled the most.

Then you trickle charge via a small dc dc converter the LA starter battery.

 

[mikeboatboy]

Hi Deeuubee, here is the charger I was thinking to buy. But now I see some comments saying once the AGM is charged, the shore charger will slow to a trickly and not pump out the extra amps for the DC/DC charger.

Victron | Blue Smart Battery Charger | IP67 Rated – Current Connected

www.currentconnected.com

 

[deeuubee]

@mikeboatboy - That might work for charging both. From their manual...

"A load can be applied to the battery while charging, as long as the
current draw is much lower than the rated output of the battery charger.
Reconditioning is not possible when a load is connected to the battery."

Your DC-DC is 18 amps correct? You could charge the starting battery with it while attaching the DC-DC charger to it as a load.
That's why they call'em smart chargers

You would be wise to call Victron and make sure it will do what you want.

edit: being that this charger can be used as a power supply when no battery is connected, it would seem like alternator power to the DC-DC charger
Just might work.

 

[mikeboatboy]

@deeuubee : Yes, the DC/DC I bought is 18 amp. So if a load (DC DC charger) is connected to battery being charged (AGM) it simply means that while that load is pulling amps, the AGM will not be able to be put in float mode. Once the Lithium is fully charged by the DC DC, that load will stop and the AGM will be able to be put into float mode by the shore charger.

But yeah, I will reach out to Victron and see what they say. Good idea.

 

[deeuubee]

I know you said you're limited for space, but it still might be more practical and cheaper to just get a separate 15 amp lifepo4 shore charger. In reality, you only need a maintenance charger for the start battery. It should be pretty much charged while running the boat. Use what you got. A good lifepo4 only charger has to be what, half the cost of that smart charger. Size wise you're talk about a quart of milk.

 

[Samsonite801]

That’s not what happens. In order to trigger the dc dc , you will need to set a high enough setpoint on your dc dc. But your mains charger will be in float mode at around 13.6-13.8 hence your dc dc will not switch on.

Hence you will need to set the dc dc set point lower resulting in overcharging the AGMs. ( which they actually don’t like ).

Charging a lithium source from an AGM which is simultaneously being fed by a dc charge source ( alternator solar or mains charger ) is just a bad idea. It will result the lead acid chemistry being charged incorrectly

A proper Li system has all charge sources including the alternator compatible with and connected to the Li bank on the basis this is the bank being cycled the most.

Then you trickle charge via a small dc dc converter the LA starter battery.

It is really what happens though... Not really sure I understand what you mean exactly. Looking at the Victron specs for the 12-12-18 it has an input range of 8-17v. When configured as such, it is a battery charger on the output (which knows about LFP charge profiles), using a variable DC input.

Ref to Specs:

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-Smart-DC-DC-chargers-isolated-250-400W-EN.pdf

It is configured to charge the LFP bank (it is a battery charger afterall), and can be triggered-on using 'Engine shutdown detection override' (via a trigger relay, triggered by shore power), or by using the manual override function (on a relay, triggered by shore power)...

My preferred option was be to just get a different LFP charger for the LFP bank (as I also indicated in my original post), but this way would work too if set up right (allow the Engine shutdown detection override feature to enable charging while the shore charger is plugged in, essentially the shore charge just acting like an alternator on the engine).

The main shore charger would do what it needs to keep the AGM battery charged (charge on appropriate charge cycle), it's not going to hurt it, the Victron will just draw the amps it needs spilling off the top of the shore charger, no matter what charge cycle it is operating in at the time (providing the voltage is anywhere between 8-17v DC).

Ref to Manual:

https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/Orion-Tr_Smart_DC-DC_Charger-en.pdf

EDIT:
I am also speaking in the context that the Victron DC-DC charger would be configured in 'Charger' mode...

 

[Goboatingnow]

@deeuubee : Yes, the DC/DC I bought is 18 amp. So if a load (DC DC charger) is connected to battery being charged (AGM) it simply means that while that load is pulling amps, the AGM will not be able to be put in float mode. Once the Lithium is fully charged by the DC DC, that load will stop and the AGM will be able to be put into float mode by the shore charger.

But yeah, I will reach out to Victron and see what they say. Good idea.

It all depends on the voltage setpoints , in reality you need to set the dc dc “ on” setpoint somewhere in the “bulk “ voltage range. This will result in current being split between the LA battery and the dc dc converter , as the LA charges the voltage will rise and both the battery and the dc charger will be supplying current to the dc dc convertor , this is especially true if the charger is not very powerful. Eventually the starter will charge fully and the voltage setpoint may rise ( depending on the dc dc converter load ) to trigger the absorption mode , the issue here is absorption mode may continue for far too long due to the dc dc load, many poor quality mains charger didn’t have limit to absorption time , so the load means the fully charged LA battery got exposed to far too long an absorption time , resulting in overcharged lead acids and subsequent damage

If the absorption protection timer trips , then the charger will drop to float mode , again the dc dc convertor will now discharge the battery until bulk mode triggers again on the charger ( in the newer victron this is configurable ) then the charge cycle begins anew exposing the LA battery to a new extended absorption cycle.

So called smart chargers operating in a system where loads remain on during charging have often resulted in baked batteries. This is true where a dc dc load is present and particularly where the load is a high proportion of charger capacity

Tail current measuring helps as it forces the charger ( if it has enough smarts ) to adopt a partial “ power supply mode “ ie stay in bulk mode much longer possibly for very long periods.

Where dc dc charging is desired , it’s best to accept that the battery basically charges the other battery and the mains charger recharges the battery. Paradoxically the alternator is better because car stock alternators are designed as power supplies not battery chargers , hence they have a fixed voltage ouput typically near the top of the bulk voltage point. Thus means however they can undercharge batteries that also have permanent loads especially where run times are short.

 

[Goboatingnow]

It is really what happens though... Not really sure I understand what you mean exactly. Looking at the Victron specs for the 12-12-18 it has an input range of 8-17v. It is a battery charger on the output (which knows about LFP charge profiles), using a variable DC input.

Ref to Specs:

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-Smart-DC-DC-chargers-isolated-250-400W-EN.pdf

It is configured to charge the LFP bank (it is a battery charger afterall), and triggered-on using 'Engine shutdown detection override', or the manual override function...

My preferred option was be to just get a different LFP charger for the LFP bank (as I also indicated in my original post), but this way would work too if set up right (allow the Engine shutdown detection override feature to enable charging while the shore charger is plugged in, essentially the shore charge just acting like an alternator on the engine kind of like).

The main shore charger would do what it needs to keep the AGM battery charged (charge on appropriate charge cycle), it's not going to hurt it, the Victron will just draw the amps it needs spilling off the top of the shore charger, no matter what charge cycle it is operating in at the time.

Ref to Manual:

https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/Orion-Tr_Smart_DC-DC_Charger-en.pdf

The engine on detection feature of these relies on a smart alternator whose voltage is variable and rises when the engine is on , if you have a stock alternator , you will have a fixed voltage and will not be truly able to detect engine on. The situation is worse where a mains charger is charging as well as the dc dc operating

The best bet is always to charge the Li bank directly from all charge sources , with all such sources ( mains , solar and alternator) profiled for lithium charging.

You then trickle charge the starter using a cheap low current dc dc converter driven by the lithium power pack. Yiu don’t care about dc dc and charging interaction, your Li power pack simply isnt concerned about a few amps and the technology doesn’t get bothered by undercharging

 

[Samsonite801]

The engine on detection feature of these relies on a smart alternator whose voltage is variable and rises when the engine is on , if you have a stock alternator , you will have a fixed voltage and will not be truly able to detect engine on. The situation is worse where a mains charger is charging as well as the dc dc operating

The best bet is always to charge the Li bank directly from all charge sources , with all such sources ( mains , solar and alternator) profiled for lithium charging.

You then trickle charge the starter using a cheap low current dc dc converter driven by the lithium power pack. Yiu don’t care about dc dc and charging interaction, your Li power pack simply isnt concerned about a few amps and the technology doesn’t get bothered by undercharging

I do agree with you that it would be easier to just wire in another LFP charger.

My only point was that the other way is a potential option if someone wanted to go through the trouble. The engine shutdown detection has an override, you just apply a trigger voltage using a relay which you wire in to close when shore power is applied and it will turn on the Victron charger. There could be reasons why some people may want to do it that way.

I do think it would be easier to just wire in another LFP charger though, same like you're saying.


Ref:

 

[mikeboatboy]

I was planning to not use the engine detection, and instead install a switch next to the ignition, to turn on the DC/DC charger when I want to. I may not always want the DCDC charger on, for example at idle my little 35amp alternator may struggle.

I don't have the budget to buy a special smart alternator, that's why I decided to keep everything the same and deal with the Lithiums this way.

 

[Samsonite801]

I was planning to not use the engine detection, and instead install a switch next to the ignition, to turn on the DC/DC charger when I want to. I may not always want the DCDC charger on, for example at idle my little 35amp alternator may struggle.

I don't have the budget to buy a special smart alternator, that's why I decided to keep everything the same and deal with the Lithiums this way.

Yeah the 'Engine shutdown detection override' essentially means the same thing as manually triggered user-toggled method of charger turn-on hehe...

 

[Goboatingnow]

I think you miss the point , you can’t have engine on detection , yiu don’t want to force the dc dc on as thatv will deplete the starter as it tries to power the dc dc

This is the issue. If you have a standing load on a battery not designed for such an eventually , then you actually need power supplies , ie fixed voltage sources, like a stock alternator. This prevents battery cycling which will damage it ( this is what’s used in a car )

However if your charge sources are multi stage battery chargers , these are less and less suitable where standing loads like the dc dc convertor remain in place. Smart chargers work best when the battery is unloaded during charging.

Hence a dc dc convertor from a battery not designed for deep cycling , like your starter , is a far less proper approach then a dc dc converter powered by a big deep cycle capable power bank which is charging or merely trickle charging a small starter battery.

 

[Samsonite801]

I think you miss the point , you can’t have engine on detection , yiu don’t want to force the dc dc on as thatv will deplete the starter as it tries to power the dc dc

This is the issue. If you have a standing load on a battery not designed for such an eventually , then you actually need power supplies , ie fixed voltage sources, like a stock alternator. This prevents battery cycling which will damage it ( this is what’s used in a car )

However if your charge sources are multi stage battery chargers , these are less and less suitable where standing loads like the dc dc convertor remain in place. Smart chargers work best when the battery is unloaded during charging.

Hence a dc dc convertor from a battery not designed for deep cycling , like your starter , is a far less proper approach then a dc dc converter powered by a big deep cycle capable power bank which is charging or merely trickle charging a small starter battery.

First off, this isn't just a DC-DC converter, it is also a DC-DC charger. And if you have a good AGM starter battery, why would 18a deplete the starter during cranking?

Also he said he has a toggle on it, so he'll just shut it off for a minute if he thought it would be too much load on his AGM battery while starting.

And if it's still plugged into the shore charger, and if the shore charger is sufficiently large enough to handle both charging on the AGM and feeding the DC-DC charger as it should be sized, then it should all be full and floating when you might be going in there to start it.

And if you disconnect the shore power, you just shut off the DC-DC charger and it won't drag on the AGM circuit.

I'm not sure I understand what you mean about deep cycling batteries, the two circuits are isolated and we're not bringing either one of them down here, just floating on shore power at the dock, everything's full...

 

[deeuubee]

If you don't use the ignition sense the won't the Victron charger use the start battery as an input. So at most 18 amps out. With 5 amps max in from the shore charger, you could deplete the start battery before the house battery is charged. You really need the second charger.

Is the 5 amp charger bolted in or portable? It was fine for a maintenance charger when both house and start we're Lead Acid, but overkill as a maintenance charger just for the start battery.

Just to give you another rabbit hole to go down...
I have LA and Lifepo4 in my RV.
When plugged in, I have a separate lifepo4 charger for house and run a small 2 amp DC-DC charger off of the lifepo4 as a maintenance charger for the Lead battery.