Can DC to DC Convertors ruin your battery?

[rom]

Originally Posted by Pelagic

Hi Rom,
Yes the 12v is recharged by my 12kw Northern Lights Gen. But that battery also serves a small number of 12v consumers.

The DC to DC is supposed to just keep it topped up if I dont use the Gen for a few days...... All my main consumers are 24v

ok good, so just disconnect that 12V genset start battery from the 12V system and you're done !

Some people here successfully rely on a DC-DC converter to supply their 12V system. The pros is that voltage doesn't fluctuate. The cons is that if the DCDC converter fails you don't have anymore intruments ... Maybe 2 smaller DC-DC converters in parallel would be a good solution for redundancy.

[Pelagic]

Originally Posted by rom

ok good, so just disconnect that 12V genset start battery from the 12V system and you're done !
.

Never thought of doing that Rom
I guess I saw that battery as more of an emergency Radio Battery.
It is stored high in the pilothouse under the port console in a locker under the wheel.

Keeping that battery properly regulated is I think the best solution

[Pelagic]

Originally Posted by Fuss

Based on the information you supplied, I think there is no overcharging.
There a drain on the 12v battery apart from starting the generator as it powers instruments. This means that the battery is being drained when the generator is in use and maybe even when it is off (Please check if the battery is being used when the generator is off). Also, the way 24v to 12v chargers work is that when the house bank is being charged (over 26v) then the 12v battery gets charged at 13.7v. The 12v battery gets no charge when the house bank is not being charged.....can you check if this is the case for you).

This could lead to situations where your 12v battery has been drained and not recharged for a few days, which has maybe caused the shortened life.

The correct way to set this up is as follows...

1/ A 24v-12v converter should be used to power all 12v things onboard from the 24v house bank. Mastervolt makes a 20a version that can be paralleled if 20a is not enough.

2/ A 24v -12v charger that charges the generator battery whenever the 24v house bank hits 26v. This charger needs only to be 10a at the most.

3/ The generator should charge the 12v battery when it is running. You can do this by installing a very small 15a 12v alternator or buy a Victron 15a 12v charger powered by AC when the generator is running.

Hi Fuss
That 12v battery supplies things like chart lights both VHF & SSB /AIS... Gas Alarms and my AC board LED Display

As I mentioned to Rom, having a 14v battery for radios is a safety thing for me

My Gen does have a 12v Alternator so Batt it is quickly toped up when the Gen is on.
if you look at the Trojan Battery data sheet it stated charge to
And Float to

My Victron DC/DC simply holds it @ 13.7v on regardless of what is turned on

[Pelagic]

Originally Posted by Fuss

Based on the information you supplied, I think there is no overcharging.
There a drain on the 12v battery apart from starting the generator as it powers instruments. This means that the battery is being drained when the generator is in use and maybe even when it is off (Please check if the battery is being used when the generator is off). Also, the way 24v to 12v chargers work is that when the house bank is being charged (over 26v) then the 12v battery gets charged at 13.7v. The 12v battery gets no charge when the house bank is not being charged.....can you check if this is the case for you).

This could lead to situations where your 12v battery has been drained and not recharged for a few days, which has maybe caused the shortened life.

The correct way to set this up is as follows...

1/ A 24v-12v converter should be used to power all 12v things onboard from the 24v house bank. Mastervolt makes a 20a version that can be paralleled if 20a is not enough.

2/ A 24v -12v charger that charges the generator battery whenever the 24v house bank hits 26v. This charger needs only to be 10a at the most.

3/ The generator should charge the 12v battery when it is running. You can do this by installing a very small 15a 12v alternator or buy a Victron 15a 12v charger powered by AC when the generator is running.

Hi Fuss
That 12v battery supplies things like chart lights both VHF & SSB /AIS... Gas Alarms and my AC board LED Display

As I mentioned to Rom, having a 12v battery for radios is a safety thing for me

My Gen does have a 12v Alternator so Battery is quickly toped up when the Gen is on.
if you look at the Trojan Battery data sheet states it should be charged up to 14.7V and Float at 13.5V

My Victron DC/DC simply holds it @ 13.7v on regardless of what is turned on.



It never sees 14.7 except maybe when the Gen is on, which is rare these days.

I guess the DC/DC is not smart enough for the AGM, which is why I'm thinking a smart 3 stage small 12v Charger is the best solution

What am I missing in my logic?

[Pelagic]

Originally Posted by K_V_B

I once was on a boat where they'd actually had a small AC charger connected to the inverter to charger the generator's batteries.

I think that is what I'm leaning towards
Before when it was a basic lead acid battery, it needed more water than the others and was always the first to go.

I have 11 x 8D batteries

[Adrian Chen]

Originally Posted by smac999

the vicrons are single stage charger. a good charger is 3 stage. will charge at ~14.5 bulk and ~13.5 float. so you are undercharging while the battery is low, and overcharging while it is full. both cause harm... it would take a little life off. but 3x less seems excessive.

I don't know if you can get a 3 stage 24-12 charger. somebody probably makes one.

Mastervolt Mac/Magic are 3 stage chargers available in a range of configurations.

I use them on our Southerly to charge the remote banks forthrusters and engine start all of which are AGM.

Theyve been fine

[rom]

Originally Posted by Pelagic

I think that is what I'm leaning towards
Before when it was a basic lead acid battery, it needed more water than the others and was always the first to go.

I have 11 x 8D batteries

I also think the AC charger is a good *part of the* solution, in case the genset doesn't properly do the job already. (from your description I do not really understand that part of your system.)

I did not make myself clear enough: when I say "disconnect" the starter batt I don't mean "get rid of". So that battery will still be there as an emergency if that is what you want.
To disconnect it from the 12V system you may use an ON/OFF bluesea switch, in case the DC/DC fails, just switch it ON !

of course those are just suggestions and based on my limited understanding of your system.

[Fuss]

Originally Posted by Pelagic

Hi Fuss
That 12v battery supplies things like chart lights both VHF & SSB /AIS... Gas Alarms and my AC board LED Display

As I mentioned to Rom, having a 12v battery for radios is a safety thing for me

My Gen does have a 12v Alternator so Battery is quickly toped up when the Gen is on.
if you look at the Trojan Battery data sheet states it should be charged up to 14.7V and Float at 13.5V

My Victron DC/DC simply holds it @ 13.7v on regardless of what is turned on.



It never sees 14.7 except maybe when the Gen is on, which is rare these days.

I guess the DC/DC is not smart enough for the AGM, which is why I'm thinking a smart 3 stage small 12v Charger is the best solution

What am I missing in my logic?

In later posts you say that when it was lead acid, it used more water than the others and had the shortest life. This usually means high charge voltage or the location is too hot.

What is the voltage when the generator is running? (maybe the generator alternator is overcharging it)

Is there ever a situation where the dc to dc converter is off?

Also, I also don't understand why your Victron dc to dc converter is not stressed trying to maintain 13.7v when the battery is not holding charge. If it is one of the 12amp models then it would be running at full capacity and be quite hot.

[Colin A]

Originally Posted by Pelagic

Hi Fuss
That 12v battery supplies things like chart lights both VHF & SSB /AIS... Gas Alarms and my AC board LED Display

As I mentioned to Rom, having a 12v battery for radios is a safety thing for me

My Gen does have a 12v Alternator so Battery is quickly toped up when the Gen is on.
if you look at the Trojan Battery data sheet states it should be charged up to 14.7V and Float at 13.5V

My Victron DC/DC simply holds it @ 13.7v on regardless of what is turned on.



It never sees 14.7 except maybe when the Gen is on, which is rare these days.

I guess the DC/DC is not smart enough for the AGM, which is why I'm thinking a smart 3 stage small 12v Charger is the best solution

What am I missing in my logic?

Me personally I would run the electronics directly off the converter and have on-on switch to switch over to the battery if it failed.

[john61ct]

Sorry did not read the whole thread.

A converter that is not a proper batt charger can be used to directly power the loads.

There are little "battery backup" boxes that pass thru the power supply, but if (and only if) that's interrupted then switch to battery. Just rickle charges once power returns, so not suitable for a pricey backup bank. Samlex is good, not expensive.

A proper DC-DC charger, like CTEK Dual or Sterling BB series, is required if you need a quality bank on the 12V side

but it's not clear to me that that's the case from the OP.

[sailorchic34]

I used a Mascot 2544 DC to DC charger for my group 27 windlass battery. It's a water proof 3 stage 2 amp charger, with 14.6 peak voltage, with boost, absorption and 13.4v float. It uses a buck converter to raise the inlet voltage to output voltage setting.

It comes with a remote mount tricolor led light to show charge mode. I also added a switch to turn it off after the battery reaches float. It works like a charm. Of course I found it last year on ebay for $12. Normally $150 ish. It works very well.

[roland stockham]

Why are you running AGM for this application? Effectively the 12v battery is simply a ballast on the system to smooth out the DC converter and give you a backup. The main advantages of AGM are low self discharge rates and slightly more compact size. Neither would seem to be an advantage here as you are not cycling the battery. A FLA cell will last much longer and is much cheaper. The charger should ideally be 13.2-13.4 but running at 13.7 will not seriously effect an FLA. I think this is probably a case where a heavy duty car battery may be the most economical choice. My only worry with this setup would be that starting the geny will cause all sorts of voltage drops and spikes that the instruments wont like.

[smac999]

Originally Posted by roland stockham

The main advantages of AGM are low self discharge rates and slightly more compact size.

the main advantage is no disgusting and toxic fluids splashing around. I will never own another flooded battery. in a car / boat / anywhere.

[Pelagic]

Originally Posted by roland stockham

Why are you running AGM for this application? Effectively the 12v battery is simply a ballast on the system to smooth out the DC converter and give you a backup. The main advantages of AGM are low self discharge rates and slightly more compact size. Neither would seem to be an advantage here as you are not cycling the battery. A FLA cell will last much longer and is much cheaper. The charger should ideally be 13.2-13.4 but running at 13.7 will not seriously effect an FLA. I think this is probably a case where a heavy duty car battery may be the most economical choice. My only worry with this setup would be that starting the geny will cause all sorts of voltage drops and spikes that the instruments wont like.

I am with Smac on staying with the AGMs as well as more efficient storage because you don't need to service them

10 of my 11 batteries are either house or main engine, so keeping them all the same seemed like a good idea.
If you look at the Trojan PDF on my Post #12 they are a dual purpose Deep Cycle so plenty of reserve for starting Gen..

Specs say a Daily charge to 14.1-14.7V and Float at 13.5
I just can't do that with my old Victron Orion DC/DC convertor

That's why a small 3 stage battery charger 20-30amps running of 24v Invertor would keep it happy.

It is easy for me to turn off the DC/DC at breaker panel, so it doesn't overcharge, but I would have to keep remembering and playing with it....Guaranteed I'd forget!

[rom]

Originally Posted by roland stockham

Why are you running AGM for this application? Effectively the 12v battery is simply a ballast on the system to smooth out the DC converter and give you a backup. The main advantages of AGM are low self discharge rates and slightly more compact size. Neither would seem to be an advantage here as you are not cycling the battery. A FLA cell will last much longer and is much cheaper. The charger should ideally be 13.2-13.4 but running at 13.7 will not seriously effect an FLA. I think this is probably a case where a heavy duty car battery may be the most economical choice. My only worry with this setup would be that starting the geny will cause all sorts of voltage drops and spikes that the instruments wont like.

One more vote for disconnecting that battery from the rest of the 12V system I guess.