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Old 23-01-2018, 19:10   #1
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Can DC to DC Convertors ruin your battery?

Stargazer came with a Victron 24v to 12v DC TO DC Convertor
for my single 12v D size battery that starts the Generator and powers the Instruments

It does not have its own charger, but depends on the DC-DC feed from my 24v House Batteries when the Generator is not running (95% of the time)

When on it stays at 13.7v, but is failing after only 2 years (AGM BATTERIES)

Compared to my 24 v system which is about 7 years

Is the DC-DC overcharging and is there a better solution?
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Old 23-01-2018, 19:54   #2
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Re: Can DC to DC Convertors ruin your battery?

13.7 is too high for float and too low for charging. It depends on the brand and temperature but AGMs should be charged at about 14.4 and float at about 13.2. Under charging is death to AGMs.
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Old 23-01-2018, 21:04   #3
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Re: Can DC to DC Convertors ruin your battery?

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.
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Old 23-01-2018, 21:52   #4
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Re: Can DC to DC Convertors ruin your battery?

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Originally Posted by Captain Bill View Post
13.7 is too high for float and too low for charging. It depends on the brand and temperature but AGMs should be charged at about 14.4 and float at about 13.2. Under charging is death to AGMs.
Thanks Bill and Smac.
Sort of what I was afraid of!

Before I switched to AGM, I used to add quite a bit of water to the 12v Battery

Are there "smarter" DC to DC convertors or is the solution to buy a small 3 stage 12v charger and power it via the Invertor.

I have a large 24v house bank (1040 Ah @24v) and 1038 w of Sunpower Solar.
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Old 23-01-2018, 22:17   #5
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Re: Can DC to DC Convertors ruin your battery?

sterling power makes a lot of stuff. here is one of there models that would likly work good. it's probaly a lot more amps then you need though. it would be like 70a output. the BB241235 at the bottom

https://sterling-power.com/collectio...rip-proof-ip21

they proabbly make others you can search through.
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Old 23-01-2018, 22:45   #6
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Re: Can DC to DC Convertors ruin your battery?

Sticking with Victron, this 3 stage Charger Centaur comes in a 12v/30 amp seems to be right and it has universal power.
https://www.victronenergy.com/charge...harger-12v-24v
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Old 23-01-2018, 23:00   #7
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Re: Can DC to DC Convertors ruin your battery?

that won't work. it's an AC charger. works if dc input over 90v
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Old 23-01-2018, 23:17   #8
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Re: Can DC to DC Convertors ruin your battery?

Victron Orion-Tr DC-DC Converters Non-isolated (24/12-10)
Datasheets This are Battery charger.

Isolated versions (no common ground) Datasheets They are configurable regarding the output voltage. More a power supply than a charger.
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Old 23-01-2018, 23:44   #9
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Re: Can DC to DC Convertors ruin your battery?

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Victron Orion-Tr DC-DC Converters Non-isolated (24/12-10)
Datasheets This are Battery charger.

Isolated versions (no common ground) Datasheets They are configurable regarding the output voltage. More a power supply than a charger.
probably what he has, they are single stage.
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Old 23-01-2018, 23:54   #10
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Re: Can DC to DC Convertors ruin your battery?

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.
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Old 23-01-2018, 23:57   #11
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Re: Can DC to DC Convertors ruin your battery?

There are also 3-state charger / booster used to charge the bord battery from the generator :

Votronic charger-booster

But in your case, the charger remains all the time connected and is not invoked only when the engine runs, so it would perform the 3-stage charging only once after installation and then it will stick to float. So there is no point for a 3-stage charger, it will never repeat the charging program unless you disconnect / reconnect the 24V battery. Also they are usually programmed only to kick in when the primary battery is charged based on charging voltage (26.4V), without a charging source there will be no power transfer from house to 12V battery...
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Old 24-01-2018, 00:04   #12
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Re: Can DC to DC Convertors ruin your battery?

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Originally Posted by smac999 View Post
that won't work. it's an AC charger. works if dc input over 90v
My thought is that I would just run it of my 3000W Mult Invertor

Either the 12/20a or 12/30a charger per Datasheet.

My 12V AGM is a 230AH Trojan so I think the 30a is per the recommended size but as I also have the DC/DC convertor, the 20a to keep it on float is probably sufficient.

How many watts out of my Invertor would the 30a take?
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Old 24-01-2018, 01:17   #13
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Re: Can DC to DC Convertors ruin your battery?

Maybe I missed something but why don't you just disconnect that 12V battery from the 12V system ? Doesn't the genset recharge its own start battery ? If not, then whatever small & cheap 3 state charger will do the job, no problem if it runs on AC, as you will not need to charge that start battery so much anyway.
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Old 24-01-2018, 01:26   #14
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Re: Can DC to DC Convertors ruin your battery?

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Originally Posted by Pelagic View Post
Stargazer came with a Victron 24v to 12v DC TO DC Convertor
for my single 12v D size battery that starts the Generator and powers the Instruments

It does not have its own charger, but depends on the DC-DC feed from my 24v House Batteries when the Generator is not running (95% of the time)

When on it stays at 13.7v, but is failing after only 2 years (AGM BATTERIES)

Compared to my 24 v system which is about 7 years

Is the DC-DC overcharging and is there a better solution?
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.
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Old 24-01-2018, 01:31   #15
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Re: Can DC to DC Convertors ruin your battery?

Quote:
Originally Posted by rom View Post
Maybe I missed something but why don't you just disconnect that 12V battery from the 12V system ? Doesn't the genset recharge its own start battery ? If not, then whatever small & cheap 3 state charger will do the job, no problem if it runs on AC, as you will not need to charge that start battery so much anyway.
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
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