Which Victron DC-DC converter to use?

[dj195]

Hi Team, I have been reading over the forums, and it has answered many questions, but also raised a few questions.

I have ordered two Victron DC-DC converter, but am now questioning if I have ordered the correct ones.

Converter 1 - Victron DC-DC 12/12 30Amp - Non-isolated

I plan to put this in my boat to use the starter/alternator to charge my 120Ah Lithium battery. I will add more Lithium's over time.

My boat motor is a Honda 60 outboard. The specs say it produces a charge current of up to 17Amps. Therefore do I need to scale my converter back to a 12/12-18Amp which seems to be the smallest smart converter? This is an isolated converter, but I know from this forum that I should use a single negative/ground.

Converter 2 - Victron DC-DC 24/12-30Amp - Non-isolated
This converter is to go into my Kart racing trailer.

I have two separate battery banks in my trailer. I have two 24V Lithium batteries in parallel that are charged from solar and the grid or a generator (if required). These run everything, both AC and DC.

I have a separate 12V 130ah deep cycle flooded battery that only runs my caravan movers on the trailer. That way, at the end of a long race weekend, when the lithium's are down, I still have power to move my trailer (oh, and the caravan movers are 12V's, and use too many amps to get the 24V's down to 12V's).

Again, is the 30Amp converter too big, or will it work OK? Also, is it fine to share the negative/ground across 24V's and 12V's, or should I get an isolated converter in this case and keep the negatives separate? The price difference is minimal.

Any help would be appreciated. thanks in advance.

 

[Dooug]

The 12/12/30 will attempt to put out 30 amps and will take in more than 30 amps, it will undoubtedly overwhelm your charging system. The 12/12/9 is your best bet, however it will still draw over 50% of your charging system capacity.

If your lithiums are down, how would the 24/12/30 charge your AGM? Otherwise the 24/12/30 should work just fine. You may be running the generator to charge the 24v to run the 24/12 converter. Maybe just a good AC charger off the generator to charge the AGM?
I don't fully understand the caravan set up.

 

[mikefitz]

N

30Amp converter too big, or will it work OK? Also, is it fine to share the negative/ground across 24V's and 12V's

I cannot see any problems with common negatives. The 30A Otion tri smart charger has cut in and cut out voltage settings related to alternator charging of the starter battery. Switch on when the voltage exceeds a certain level, and off when the volts fall below a level. These are user programmable via the Victron app. So could be set for the lithium battery, say on at volts over 26.0 volts and off at voltages below 25 volts.

 

[dj195]

The 12/12/30 will attempt to put out 30 amps and will take in more than 30 amps, it will undoubtedly overwhelm your charging system. The 12/12/9 is your best bet, however it will still draw over 50% of your charging system capacity.

If your lithiums are down, how would the 24/12/30 charge your AGM? Otherwise the 24/12/30 should work just fine. You may be running the generator to charge the 24v to run the 24/12 converter. Maybe just a good AC charger off the generator to charge the AGM?
I don't fully understand the caravan set up.

The 12/12/30 will attempt to put out 30 amps and will take in more than 30 amps, it will undoubtedly overwhelm your charging system. The 12/12/9 is your best bet, however it will still draw over 50% of your charging system capacity.

If your lithiums are down, how would the 24/12/30 charge your AGM? Otherwise the 24/12/30 should work just fine. You may be running the generator to charge the 24v to run the 24/12 converter. Maybe just a good AC charger off the generator to charge the AGM?
I don't fully understand the caravan set up.

Thanks Dooug. Will the 12/12/9 be ok for charging lithium, noting it is not a smart charger? 12/12/18 appears to be the smallest smart charger, would that also be too big?

 

[Dooug]

I missed that it wasnt a smart charger, not sure on that. Personally, i would use it but would have it switch controlled so it was off when i didnt need it running as it will push 9 amps all the time.

The 12/12/18 is also too big. Unfortunately they cannot have the output current lowered, so with a low state of charge is will try and put out 18 amps. Which will take close to 20-22 amps input which totally kills your charging system.

What loads are you powering in the boat? Im guessing a depth sounder, maybe a trolling motor? Im digging around to try and find something for you.

 

[Dave in AZ]

Honda outboard motor, isn't that alternator all built into the motor and expensive? Like, NOT a cheap automobile bolt on you get at autozone for $100? You're talking about an expensive alternator built to run an outboard, not something built to power a car's interior needs here. 17A, that means like 10A max continuous without burning up your alternator, of which most of that is probably used by motor! My Toyota at idle with not a single electrical thing on, uses 11.2A just to run the engine!

Even on my 130A car alternator, I can't suck off 30A 12v on a dcdc charger when running car loads full, around 55A use, without overheating alternator at 85A total, and that still is 45A "below stated max".

Basically I'm saying, you're going to burn your expensive difficult to replace outboard alternator out, and the most you could even pull before burning it out at 100% load is like 8A, so not even as much as a 10A cigarette lighter in your car! 96w isn't worth jacking up your Honda outboard motor.

For 96w, you could buy a 230ah battery for $650 giving as much power as running that engine for 40 hours! 45lbs, schlep it off boat if needed to charge.

I just called My Honda Marine dealer, you got me interested. He checked it, 17A 60hp. That new alternator is $799.34. He said they come in pretty often, burned out, when guys use their starter batteries too low running lights and fishfinders etc, and the alternator is only intended to replace small boat loads from starter battery.

 

[dj195]

Honda outboard motor, isn't that alternator all built into the motor and expensive? Like, NOT a cheap automobile bolt on you get at autozone for $100? You're talking about an expensive alternator built to run an outboard, not something built to power a car's interior needs here. 17A, that means like 10A max continuous without burning up your alternator, of which most of that is probably used by motor! My Toyota at idle with not a single electrical thing on, uses 11.2A just to run the engine!

Even on my 130A car alternator, I can't suck off 30A 12v on a dcdc charger when running car loads full, around 55A use, without overheating alternator at 85A total, and that still is 45A "below stated max".

Basically I'm saying, you're going to burn your expensive difficult to replace outboard alternator out, and the most you could even pull before burning it out at 100% load is like 8A, so not even as much as a 10A cigarette lighter in your car! 96w isn't worth jacking up your Honda outboard motor.

For 96w, you could buy a 230ah battery for $650 giving as much power as running that engine for 40 hours! 45lbs, schlep it off boat if needed to charge.

I just called My Honda Marine dealer, you got me interested. He checked it, 17A 60hp. That new alternator is $799.34. He said they come in pretty often, burned out, when guys use their starter batteries too low running lights and fishfinders etc, and the alternator is only intended to replace small boat loads from starter battery.

Hey, thanks Dave, perfect info, I will forget the DC charger! Much appreciated.

 

[mushhead]

The 12/12/30 will attempt to put out 30 amps and will take in more than 30 amps, it will undoubtedly overwhelm your charging system. The 12/12/9 is your best bet, however it will still draw over 50% of your charging system capacity.

If your lithiums are down, how would the 24/12/30 charge your AGM? Otherwise the 24/12/30 should work just fine. You may be running the generator to charge the 24v to run the 24/12 converter. Maybe just a good AC charger off the generator to charge the AGM?
I don't fully understand the caravan set up.

I have a Victron 12/12/30, and when it's cold, it'll put out as much as 45A until it warms up. And if it gets too hot, it dials back to less than 30A.

 

[65NW]

I use a victron smart solar mppt as a DC to DC converter for charging a 12v lead acid from a 48v lipo. I talked with my distributor and they said this should work but is not supported. I tried it and have had no problems.
48v to pv in
12v to batt
Loads if you want.

The advantage is you get all the smart solar charger settings like equalization and charge current.
Downside is you have to have min 5v above your output voltage so would not work in a 12 to 12 or 24 to 24 boost or isolation mode.

Before doing this with your 24v main pack, I would check the minimum PV input to charge. It works at 48v but 24v may be too low.

 

[Pi Curio]

I use a victron smart solar mppt as a DC to DC converter for charging a 12v lead acid from a 48v lipo. I talked with my distributor and they said this should work but is not supported. I tried it and have had no problems.
48v to pv in
12v to batt
Loads if you want.

The advantage is you get all the smart solar charger settings like equalization and charge current.
Downside is you have to have min 5v above your output voltage so would not work in a 12 to 12 or 24 to 24 boost or isolation mode.

Before doing this with your 24v main pack, I would check the minimum PV input to charge. It works at 48v but 24v may be too low.

Nice! Did you use a fuse, diode, or similar in the wiring to the PV in? Working on something similar and trying to figure out what needs to be done to do it right.
Thanks

 

[65NW]

Nice! Did you use a fuse, diode, or similar in the wiring to the PV in? Working on something similar and trying to figure out what needs to be done to do it right.
Thanks

I just ran a line from my lynx distribution on one of the inverter terminals. Its behind a 100a fuse, so, no. ?
No, the 100|20s have a fuse on them next to the terminal block.
I think they have a diode in them as well but there is always 48v on the PV side and its just tapers the charge when the 12v batt is full. It never sees a sunset.

 

[Lauren8363]

I just ran a line from my lynx distribution on one of the inverter terminals. Its behind a 100a fuse, so, no. ?
No, the 100|20s have a fuse on them next to the terminal block.
I think they have a diode in them as well but there is always 48v on the PV side and its just tapers the charge when the 12v batt is full. It never sees a sunset.

Can I ask how long you have had this setup in-place? This makes great sense. Wish I would have thought of it.

 

[65NW]

Can I ask how long you have had this setup in-place? This makes great sense. Wish I would have thought of it.

A couple months now. Has been working great. Always shows full charge and battery seems happy. Have not looked at the equalization history but I assume its working.
Had a time or two when my main (HV) pack disconnected due to cold temp (heater ran out of fuel) and everything for the 12v system came back online just fine once it was repowered. It handles that like the sun rising.
Also nice to see statistics on how much my 12v system consumes. 100 to 200 wh per day in my case, depending on how many times the heater fires up.
I dont have it connected to my cerbo as it would read its consumption as power input yo the system and would get confusing. Works great in standalone.

 

[cstockwell]

I missed that it wasnt a smart charger, not sure on that. Personally, i would use it but would have it switch controlled so it was off when i didnt need it running as it will push 9 amps all the time.

The 12/12/18 is also too big. Unfortunately they cannot have the output current lowered, so with a low state of charge is will try and put out 18 amps. Which will take close to 20-22 amps input which totally kills your charging system.

What loads are you powering in the boat? Im guessing a depth sounder, maybe a trolling motor? Im digging around to try and find something for you.

Thank you for posting information. I am about to install the 12/12/18 in a van to charge from a lead acid battery into a 2 100ah lifep04 battery bank. I have installed a 30amp breaker/shutoff switch to be able to shut it off when not wanting it in use or in very old weather. I was unsure it would even work but emailed the company selling them and their tech dept said it should be fine for that use. It is hard because Victron makes you check with sellers and won't offer tech support for the products.

 

[65NW]

Thank you for posting information. I am about to install the 12/12/18 in a van to charge from a lead acid battery into a 2 100ah lifep04 battery bank. I have installed a 30amp breaker/shutoff switch to be able to shut it off when not wanting it in use or in very old weather. I was unsure it would even work but emailed the company selling them and their tech dept said it should be fine for that use. It is hard because Victron makes you check with sellers and won't offer tech support for the products.

!!!
Its not a boost converter.
The PV input side needs to be at least 5v over the battery voltage. Step down only.

In my case I'm going from 48v to 12.
Other combinations would be
48, 36 to 24, 12
24 to 12

Basically, where 12v cell groups = n, you need n+1 on the PV input with n on the battery output