DC to DC charger

[jdcellarmod]

Thinking of installing a Victron charger for those days on the road when solar is not available. Can the charger be used in conjunction with an inverter (2000 watts) to run the refrigerator on electric while on the road?

Thanks, Jeff D

[StirCrazy]

HMS Beagle wrote:
How large is the LFP bank again? It sounds like the DC-DC is severely limiting the charge that could be put into even a reasonably large bank.

On a boat, where this stuff is much more advanced, you'd have an external regulator on the alternator, large cables to the house battery, and be charging them at 100A. The charge profile can be set for LFPs and is close enough that an AGM start battery will tolerate it. Even with a 160A alternator, you'd still only charge at around 100A because the external regulator has a temp sensor on the alternator, and will derate it at about 100 deg C frame temp to keep it from frying itself.

A big advantage of LFP over AGM is that its charge acceptance does not fall off rapidly as it gets close to full. It is actually that, not any ability to accept more maximum charge (often less than good AGM in similar sizes) that allows faster recharge. If you are sitting in a campsite running low and want to start the engine to charge, you want to put in 100A for half and hour, not 25A for 2 hours.

not to worried about the charge aceptance although it is definatly an advantage. I worked on boat/sub stuff for 20 years totaly different game and there was no LiFePO4. thoes altanatores were special units desinged to put out far more amps and such than any pick up truck altanator.

also depending on the size of battery some one has you might be better off putting in the 25amps for 2 hours. generaly a 1C charge (100amps on a 100ah battery) will get you the rated minimum cycles, a 0.2C charge will get you the max life which is a pretty singnificant amount of extra cycles.

think of this as just a way to suplement charging of your house batteries using a proper profile, weather you have gel, agm, flooded or Li. Myself in my camper and my 5th wheel I have no charging from the vehicle at all, but that is changing with the camper as I am putting in a 20 to 30 amp dc charger. normaly my solar panels have me charged back up before noon, but if I am camping and we get dark for quite a few days I have the dc to dc as a back up charger, or to take the 22 amps my solar puts out and add another 20 to 30 amps of output to charge even faster if I need it. if you don't have a permantly mounted solar, or you just want to run the fridge on 12V while your driving it is good there making sure to charge by the proper profile for your house batteries. it also acts as a battery seperator so you cant pull down your starting battery.

[theoldwizard1]

HMS Beagle wrote:

A big advantage of LFP over AGM is that its charge acceptance does not fall off rapidly as it gets close to full. It is actually that, not any ability to accept more maximum charge (often less than good AGM in similar sizes) that allows faster recharge.

That is pretty low on my list ! Reduced weight, no out gasing, more charge cycle per life and being able to use a much higher percentage of the capacity out rank speed of charge.

HMS Beagle wrote:
If you are sitting in a campsite running low and want to start the engine to charge, you want to put in 100A for half and hour, not 25A for 2 hours.

I would have a separate generator and charger.

[theoldwizard1]

HMS Beagle wrote:
How large is the LFP bank again? It sounds like the DC-DC is severely limiting the charge that could be put into even a reasonably large bank.

YES, a DC-DC charger DOES limit the charge rate !

• There is a big "concern" about over stressing your engine alternator.
  
• If you have a 7 pin trailer harness connector, the charge wire and fuse are probably designed for 30A. Above that, would require different/additional wiring.
  
• High current electronics are $$$ !

[HMS_Beagle]

How large is the LFP bank again? It sounds like the DC-DC is severely limiting the charge that could be put into even a reasonably large bank.

On a boat, where this stuff is much more advanced, you'd have an external regulator on the alternator, large cables to the house battery, and be charging them at 100A. The charge profile can be set for LFPs and is close enough that an AGM start battery will tolerate it. Even with a 160A alternator, you'd still only charge at around 100A because the external regulator has a temp sensor on the alternator, and will derate it at about 100 deg C frame temp to keep it from frying itself.

A big advantage of LFP over AGM is that its charge acceptance does not fall off rapidly as it gets close to full. It is actually that, not any ability to accept more maximum charge (often less than good AGM in similar sizes) that allows faster recharge. If you are sitting in a campsite running low and want to start the engine to charge, you want to put in 100A for half and hour, not 25A for 2 hours.

[otrfun]

Camper_Jeff_&_Kelli wrote:
I'm out in the TC again today idling the engine. Today I shut off all DC loads except 1 LED dinette table light. Inverter and all else is off excepting for dc electronic controls in fridge and water heater. Idling away, my input voltage is 13.6 and the output charge voltage is 13.7. The unit is hot again. It took half an hour to get to the too hot to touch point. Just guessing, 150 to 160 degrees. The unit has a large heat sink on it. Not smelling electronics. If I were to drive the truck and bring up the speed of the alternator and the output voltage, it may raise the charge voltage lowering the current and possibly the temperature. I have not felt the alternator to see what it's temp is/feels like. I'll run out and do a feel temp test on the alternator, and bring the engine up to 2K RPM for a couple minutes to see if that changes voltage readings to the DC DC input and outputs, hang on...
OK, the alternator is warm on the front just after the big radiator cooling fan, and hot a couple inches back to the rear of the alternator. The truck voltage goes from 13.6 at idle to 13.8 when revved to 2K RPM and current goes up just a little varying from 13.2 to 13.8 according to the BMS. The Victron dc dc charger only reports input and output voltage. I need to look at each battery's BMS for its report which differs and includes current. So, Engine RPM makes a small difference on my setup, I don't know if it's enough to change the time to charge or heat profile. I will have to take a drive to do that. My alternator is 160 amps so it should be able to handle the truck load and the dc to dc. It took an hour at idle to bring both batteries up to 90 and 91 percent charge. My latest weather forecast shows clouds and snow the next 6 days so I'll have to do some driving in the TC to keep the system charged. About an hour a day but tomorrow, I think I'll do some extra running around and bring the batteries back up to about 100%, then watch it slowly go down from there, with all the DC stuff that isn't necessary shut off to make things last longer.
About 5 weeks till I get the new Victron 3000 and get shore power again. Even though I installed 675 watts of solar on the roof, it just isn't enough for winter up here in the Seattle area.

Is there any particular reason you didn't mention any specific current readings? Voltage readings alone only tell us a fraction of what's going on with our dc to dc charger. Voltage is akin to water pressure. Current is similar to gauging how many gallons of water are flowing per min. One can have tons of water pressure (or voltage), but have very little to no water (or current) flowing.

To determine how efficiently our dc to dc charger is operating, we take current readings (with max rated charge current at the charger's output terminal) at the power source (i.e., TV alternator/battery terminals) and battery terminals of the battery being charged by the dc to dc charger. These two current readings determine the overall efficiency of our entire dc to dc charger installation. If the efficiency is less than desired, we'll also take voltage readings, along with additional voltage/current readings at the input and output terminals of the dc to dc charger to help locate the source of the efficiency (voltage) drop.

I can't vouch for Victron dc to dc chargers, but Renogy dc to dc chargers can achieve almost 90% efficiency IF large/short enough cables are used on the input and output (and alternator voltage is high enough relative to charge voltage). For what it's worth, our 40a Renogy dc to dc charger is roughly 90% efficient. It uses approx. 44a of alternator current to produce 40a of charge current at the battery terminals.

[theoldwizard1]

Camper_Jeff_&_Kelli wrote:
This is why you need proper equipment to charge Lithium batteries, they can accept so much current they can destroy your alternator burning it out.

The more if hear this stated, the less I believe it ! Not saying that you should NOT use a DC-DC charger.

My next rig WILL have a DC-DC charger. The biggest reason is that it will make certain the correct voltage is sent to lithium batteries from a source designed to charge lead acid batteries. (FYI - Lead acid batteries can be overcharged with little damage as long as the guild level in maintained.)

[ticki2]

What is your average daily amp hour usage

[Camper_Jeff___K]

pianotuna wrote:
Camper Jeff & Kelli,

Is there a cooling fan in the Victron dc to DC unit?

The charging total from the numbers posted suggest about 56 amp-hours went into the 400 amp-hour battery bank.

Were you driving or was this just idling the engine?

Does anyone know the efficiency numbers for the Victron dc to DC charger? (appears to be 87%)

The unit puts out 25 amps at normal input voltage, according to the pdf. That seems a bit strange to me. Perhaps I'm reading the wrong pdf? The "sales" pages says 30 amps continuous to 40 amps, at nominal out put voltage.

From that 87% it appears the alternator had to produce about 65 amp-hours.

The Victron apparently boost charges for 2 hours on the Li settings.

I know my unit does 19.6 amps. It is the 20 amp renogy unit.

I'm glad to hear yours is doing what you need!

I'm out in the TC again today idling the engine. Today I shut off all DC loads except 1 LED dinette table light. Inverter and all else is off excepting for dc electronic controls in fridge and water heater. Idling away, my input voltage is 13.6 and the output charge voltage is 13.7. The unit is hot again. It took half an hour to get to the too hot to touch point. Just guessing, 150 to 160 degrees. The unit has a large heat sink on it. Not smelling electronics. If I were to drive the truck and bring up the speed of the alternator and the output voltage, it may raise the charge voltage lowering the current and possibly the temperature. I have not felt the alternator to see what it's temp is/feels like. I'll run out and do a feel temp test on the alternator, and bring the engine up to 2K RPM for a couple minutes to see if that changes voltage readings to the DC DC input and outputs, hang on...
OK, the alternator is warm on the front just after the big radiator cooling fan, and hot a couple inches back to the rear of the alternator. The truck voltage goes from 13.6 at idle to 13.8 when revved to 2K RPM and current goes up just a little varying from 13.2 to 13.8 according to the BMS. The Victron dc dc charger only reports input and output voltage. I need to look at each battery's BMS for its report which differs and includes current. So, Engine RPM makes a small difference on my setup, I don't know if it's enough to change the time to charge or heat profile. I will have to take a drive to do that. My alternator is 160 amps so it should be able to handle the truck load and the dc to dc. It took an hour at idle to bring both batteries up to 90 and 91 percent charge. My latest weather forecast shows clouds and snow the next 6 days so I'll have to do some driving in the TC to keep the system charged. About an hour a day but tomorrow, I think I'll do some extra running around and bring the batteries back up to about 100%, then watch it slowly go down from there, with all the DC stuff that isn't necessary shut off to make things last longer.
About 5 weeks till I get the new Victron 3000 and get shore power again. Even though I installed 675 watts of solar on the roof, it just isn't enough for winter up here in the Seattle area.

[pianotuna]

Camper Jeff & Kelli,

Is there a cooling fan in the Victron dc to DC unit?

The charging total from the numbers posted suggest about 56 amp-hours went into the 400 amp-hour battery bank.

Were you driving or was this just idling the engine?

Does anyone know the efficiency numbers for the Victron dc to DC charger? (appears to be 87%)

The unit puts out 25 amps at normal input voltage, according to the pdf. That seems a bit strange to me. Perhaps I'm reading the wrong pdf? The "sales" pages says 30 amps continuous to 40 amps, at nominal out put voltage.

From that 87% it appears the alternator had to produce about 65 amp-hours.

The Victron apparently boost charges for 2 hours on the Li settings.

I know my unit does 19.6 amps. It is the 20 amp renogy unit.

I'm glad to hear yours is doing what you need!

[Camper_Jeff___K]

I ran the truck an hour and a half the other day. My Victron 30 amp dc to dc got pretty darn hot. Hotter than I wanted to touch. During that time, the 2, 200AH lifepo batteries were charged from 79% to 93% each. Minimal solar now, about 0 to 175 watts for a couple hours of winter time, low sun days. My 45 amp Boondocker has stopped working. Exterior fuses are good but there may be an interior fuse. I'll have to pull out the unit to inspect since it's in a difficult location. I plan to replace it with a Victron 3000 watt inverter charger when I get to Quartzite. This is why you need proper equipment to charge Lithium batteries, they can accept so much current they can destroy your alternator burning it out. My guess is the old boondocks couldn't handle the batteries either.

[deltabravo]

Hemi Joel wrote:
If I wanted to run a fridge while on the highway and not on propane, I would mount an inverter under the hood close to the battery, then run a 110 volt cord back to the fridge circuit.
Or you could plug the whole camper into it and the built-in charger in the camper would keep the camper batteries up.

Having the inverter in the camper is far more logical, then you hook it up to the house battery bank, not the engine start battery.

DC to DC Charger takes car of the charging needs while driving, rather than dealing with inefficiencies of inverter doing DC to AC (with underhood mounted inverter) and then the DC charger in camper converting the AC back to DC.

[Grit_dog]

^Now you guys are pickin chit with the chickens!

[Camper_Jeff___K]

StirCrazy wrote:

Camper_Jeff_&_Kelli wrote:
The best thing about Lithium is they always put out 13.2 volts thanks to the BMS. Lead batteries, all types, slowly drop voltage as they discharge causing brown out conditions like dim lights, slow pump motors, and weak other loads. Not so with Lithium. 13.2 volts stable all the way down to 80 or 90% discharge and then the BMS protection shuts it off till recharged. Lithium is like having your cake and eating it too.

now thats not true, at 90% discharged the voltage of a LiFePO4 battery is only 12.0V if you would have said they put out over 12V untill 90% discharged then yes that is true and still a huge advantage over a wet battery which hits 12V at about 50% discharged. an even better advantage of the LiFePO4 is the voltage level under load, you can discharge much deeper befor you get alarms from your inverter from low voltage. a flooded battery can drop to 11.5V at 100% charged if it has a C/3 load on it, so basicly a 100 amp battery with a 33amp load will dip pretty fast, which is why for big rigs people run 4 6V batteries or more. Lifepo4 doesnt have this issue to that degree as you can do a C1 discharge and stay above 12V to 90% discharge which would be a 100 amp draw on a 100amp battery. so in a way your right just your numbers are off a little.

I will agree that you have a more precise answer. The bigger the load, the more likely the voltage will drop and that effect will increase the more it is discharged. Nonetheless, the voltage is more stable than lead.

[StirCrazy]

pianotuna wrote:

Grit dog wrote:
Telecom jars is his nifty lingo for telecommunications backup batteries.

It is not my acronym. It is name used by the cell companies. They are a sub variant of AGM. I like them as I no longer have to lay down in the snow to do a specific gravity test.

I have noticed a whole bunch of telecom jars are going LifePo4 now. the ones you got are AGM?