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Opinions on basic truck/van charging system (All in one DC/DC/MPPT?) that will use both alternator and solar for house Lifepo4 battery

Drewgold

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Long time lurker first time poster. I know this sort of question gets asked a lot but I have been unable to find an answer to my main question which is this:

Is there some benefit to the dual input DC/DC and MPPT charge controllers (such as the offerings from Renogy) other than the saved space and somewhat simplified wiring?

I'm reluctant to go with a dual input controller for the sake of redundancy. If the dual controller were to fail, it could take the entire charging capability with it. In my mind, having a separate MPPT and DC/DC controllers adds a certain redundancy to the system should one component fail. It's also unclear whether the alternator charging can be manually switched off with the dual controller? I'd like the option to turn off alternator charging if desired. On top of this, there seems to be little or no cost savings for the dual unit vs two separate chargers. Am I missing other benefits to a dual controller other than a potentially cleaner install?

My planned power system for a small camper will use a single 100ah Lifepo4 house battery, 80w solar panel, then either a 20A Renogy MPPT solar controller with a separate 20A DC/DC charger powered by the vehicle (with 70A alternator) OR the Dual 30A DC/DC charger with MPPT.

Open to any feedback anyone may have!

And big thanks to everyone who contributes to this forum, it is an amazing resource.
 
Most decent dc-dc chargers have an MPPT input. Some will prioritize the solar power (while driving) to save alternator draw when charging your deep cycles. If you want to use a separate solar controller for redundancy that's your choice.
 
70 amp alternator, you could just run a long wire with a toggle switch back to the LFP battery. 10ga or smaller. You don't have much amperage to play with so charging from the alternator will be limited. There is no way you could run 20A or 30A DC/DC at full output without eventual failure of the alternator.

The idea of using the long wire is to create resistance in the circuit to limit charge current. You won't get full charging but if you want cheap and effective, it will work.
 
Long time lurker first time poster. I know this sort of question gets asked a lot but I have been unable to find an answer to my main question which is this:

Is there some benefit to the dual input DC/DC and MPPT charge controllers (such as the offerings from Renogy) other than the saved space and somewhat simplified wiring?

I'm reluctant to go with a dual input controller for the sake of redundancy. If the dual controller were to fail, it could take the entire charging capability with it. In my mind, having a separate MPPT and DC/DC controllers adds a certain redundancy to the system should one component fail. It's also unclear whether the alternator charging can be manually switched off with the dual controller? I'd like the option to turn off alternator charging if desired. On top of this, there seems to be little or no cost savings for the dual unit vs two separate chargers. Am I missing other benefits to a dual controller other than a potentially cleaner install?

My planned power system for a small camper will use a single 100ah Lifepo4 house battery, 80w solar panel, then either a 20A Renogy MPPT solar controller with a separate 20A DC/DC charger powered by the vehicle (with 70A alternator) OR the Dual 30A DC/DC charger with MPPT.

Open to any feedback anyone may have!

And big thanks to everyone who contributes to this forum, it is an amazing resource.
I'm in a similar situation with planning my new build and conversion to LFP batteries. In my old setup, I've just used a very simple voltage sensing relay for charging from the alternator then a very cheap 10A MPPT for charging an AGM battery.
I too am considering the 30A DC-DC/Mppt renogy charger, or maybe going to Victron for individual units tailored to amperage I expect to use.
After my recent research, I am leaning towards Victron, even though its likely to cost about 30% more.
This is primarily because one element I would like is whole of system monitoring. Whilst Renogy has bluetooth communication, its seems they run 2 seperate BT comms protocols and not all their devices have comms, you cant have a didgital dsiplay monitor adn BT monitoring at the same time and its hard to get information about it. Where as the Victron communication system seems leaps and bounds ahead, they have a huge range of devices that communicate, it can simultaneously communicate via BT or via a monitoring panel.
 
70 amp alternator, you could just run a long wire with a toggle switch back to the LFP battery. 10ga or smaller. You don't have much amperage to play with so charging from the alternator will be limited. There is no way you could run 20A or 30A DC/DC at full output without eventual failure of the alternator.

The idea of using the long wire is to create resistance in the circuit to limit charge current. You won't get full charging but if you want cheap and effective, it will work.
So you feel that even a 20A DC/DC charger would be too hard on the Alternator? The Renogy units actually allow for an accessory wire to be run, when powered it will reduce the charger output to 10A.
My truck is an older Toyota diesel so uses pretty limited power once started. I believe they came with an option for 55A alternators or an 'upgraded' 70A alternator which I have. It's an imported truck and the alternators are hard to get so I don't really want to risk cooking it. Maybe I'll have to stick at 10A to be safe.
 
So you feel that even a 20A DC/DC charger would be too hard on the Alternator? The Renogy units actually allow for an accessory wire to be run, when powered it will reduce the charger output to 10A.
My truck is an older Toyota diesel so uses pretty limited power once started. I believe they came with an option for 55A alternators or an 'upgraded' 70A alternator which I have. It's an imported truck and the alternators are hard to get so I don't really want to risk cooking it. Maybe I'll have to stick at 10A to be safe.
70a isn't much when you consider a blower motor can draw 25a on high speed. Add in lights and a few accessories and you're at 40a or more quickly.

10a is ideal for an alternator that size. Running a wire straight back can net you 10a at less cost but you won't get a full charge into the bank. It would depend on how much you want to push to the bank and your usage. Any solar?
 
@ Drewgold +I thought the higher power coming from car battery are too high and would.melt a skinnier wire? Why do you think your suggestion be safe?
 
@ Drewgold +I thought the higher power coming from car battery are too high and would.melt a skinnier wire? Why do you think your suggestion be safe?
Resistance of the wire due to long length and the size. It of course will have a fuse for the rated amps on the circuit but you won't pass full amps thru the wire. Take that long circuit and add a sizeable load such as a car headlamp to it at the far end. Measure the voltage drop from B+ to the load+. You will find out how many volts the circuit drops, this is due to resistance of the wire.

The issue with just using a simple circuit like this is due to the resistance and long length. This creates voltage drop and you will never achieve full charge of the battery. This is why many will install a B2B charger, it will step up the voltage to charge the battery to full charge. Is one needed? No, if there is solar or other charging capability such as AC/DC charger from shore power, then it might not be needed. If one just needs to have a way to charge to 75-80% and has some solar to complete to full charge, then a B2B wouldn't be needed.
 
Aww, the joys of living in a van. You haven’t told us what your power usages are. That might help… in case you are interested in a more “holistic” approach.

But, thanks for starting this thread. It somewhat touches on my questions and concerns as well. I doubt anyone here thinks I have the “cred” to make recommendations but…

* you could probably benefit from a larger solar panel
* that alternator IS small…is there an internet forum for your vehicle? Maybe someone has hacked a larger alternator (or a 2nd one) that could handle more amp draw.
* the smallest DC-DC charger I am aware of is the Victron Orion TR 12/12 - 9 (9 amp output). They also make a 12/12 - 18. I don’t know if these, or the Renogy are aware of the alternator strain while operating…or do they just suck power as hard as they can to deliver their rated output. These have no solar input, so you would need a separate solar controller…which you could probably wire in parallel…so one or the other charges (or possibly both at same time). But think about that: it would take 1 hour of driving to restore only 9ah (or 18ah or 20 with the larger units) back into your battery…and could replenish power even slower.
* you could have a dual input DC-DC / solar unit as you are asking about, and like above, wire a 2nd solar controller in parallel, perhaps with a switch; that would give you extra redundancy. Then you could even have one solar controller going to your roof (?) panel, and the second connect to a portable panel when camped…and best case, operate both simultaneously.
* most or all “affordable” dual-input units have a fairly low solar input voltage limit. That probably won’t matter with an 80w panel, but could if you upgraded to a 200+ watt, or tried to tie 2 small panels in series ( doubling the voltage).
* speaking of small panels, you might be better off with a PWM controller. Many MPPT controllers need battery voltage +5 to “wake-up” in the morning. With a lithium battery, that may mean 13.4v + 5 = 18.4v. Make sure your panel puts out more than that. One exception I know of is the CTEK dual (DS250s, -sa, -se). These wake-up at a surprisingly low solar voltage…but max out at only 23v solar input…and only the d250se has a LiFePO charge profile. Battleborn, who probably has the best (or most visible) LiFePO customer support sometimes says the CTEK d250s is OK with their batteries, and sometimes says they are not. Hmmm.
* besides Renogy, there is a Kisae Abso brand dual input unit…not sure if it is better or not…certainly less money than CTEK, Redarc or Sterling (if Sterling even has a dual input unit).
* I don’t know if any battery isolators, ACR’s or VSR’s will work with LiFePO.
* you asked about being able to switch off alternator charging. This is super easy: my CTEK is voltage sensing, but a stout switch or circuit breaker between it and the alternator assures no voltage comes through when the breaker is off. Then the CTEK operates as only a solar controller. Those units that require a separate ignition-on signal wire are even easier to mount a switch to, since that would be a low amperage wire.
 
I have a 60 amp alternatori in my rig, a '82 Vanagon. I've been using a Kisae DMT1250 unit for the last couple of years, it's working great. It's an 50 amp MPPT solar charge controller combined with a 50 amp dc/dc charger, but the charger output is full programmable. I have mine set for 25 amps, haven't had any issues. I have a 280 amp hour lithium battery it keeps charged just fine.
 
Aww, the joys of living in a van. You haven’t told us what your power usages are. That might help… in case you are interested in a more “holistic” approach.

But, thanks for starting this thread. It somewhat touches on my questions and concerns as well. I doubt anyone here thinks I have the “cred” to make recommendations but…

* you could probably benefit from a larger solar panel
* that alternator IS small…is there an internet forum for your vehicle? Maybe someone has hacked a larger alternator (or a 2nd one) that could handle more amp draw.
* the smallest DC-DC charger I am aware of is the Victron Orion TR 12/12 - 9 (9 amp output). They also make a 12/12 - 18. I don’t know if these, or the Renogy are aware of the alternator strain while operating…or do they just suck power as hard as they can to deliver their rated output. These have no solar input, so you would need a separate solar controller…which you could probably wire in parallel…so one or the other charges (or possibly both at same time). But think about that: it would take 1 hour of driving to restore only 9ah (or 18ah or 20 with the larger units) back into your battery…and could replenish power even slower.
* you could have a dual input DC-DC / solar unit as you are asking about, and like above, wire a 2nd solar controller in parallel, perhaps with a switch; that would give you extra redundancy. Then you could even have one solar controller going to your roof (?) panel, and the second connect to a portable panel when camped…and best case, operate both simultaneously.
* most or all “affordable” dual-input units have a fairly low solar input voltage limit. That probably won’t matter with an 80w panel, but could if you upgraded to a 200+ watt, or tried to tie 2 small panels in series ( doubling the voltage).
* speaking of small panels, you might be better off with a PWM controller. Many MPPT controllers need battery voltage +5 to “wake-up” in the morning. With a lithium battery, that may mean 13.4v + 5 = 18.4v. Make sure your panel puts out more than that. One exception I know of is the CTEK dual (DS250s, -sa, -se). These wake-up at a surprisingly low solar voltage…but max out at only 23v solar input…and only the d250se has a LiFePO charge profile. Battleborn, who probably has the best (or most visible) LiFePO customer support sometimes says the CTEK d250s is OK with their batteries, and sometimes says they are not. Hmmm.
* besides Renogy, there is a Kisae Abso brand dual input unit…not sure if it is better or not…certainly less money than CTEK, Redarc or Sterling (if Sterling even has a dual input unit).
* I don’t know if any battery isolators, ACR’s or VSR’s will work with LiFePO.
* you asked about being able to switch off alternator charging. This is super easy: my CTEK is voltage sensing, but a stout switch or circuit breaker between it and the alternator assures no voltage comes through when the breaker is off. Then the CTEK operates as only a solar controller. Those units that require a separate ignition-on signal wire are even easier to mount a switch to, since that would be a low amperage wire.
Impatient, regarding:"
Those units that require a separate ignition-on signal wire are even easier to mount a switch to, since that would be a low amperage wire.",

I'm new to this. Hope its ok to ask this question. Are you saying that, (If i got a dc-dc -say a Renogy 20amp- no mttp), the ignition wire can just go to an on/off switch? Two wires? A pos &a neg? No need to wire it in to a hot or ignition fuse? And the positive power would go back to the starter battery? And the neg would be grounded to house battery or vehicle ? Just trying to understand. Thanks
 
I want someone with direct Renogy experience to answer Sea’s question. I don’t have direct Renogy experience.

But what I “thought” was that there would be a “high” current positive wire, and maybe a “high” current neg (or chassis ground), which the actual charge current is passing through, but also a separate (3rd) “on-off” wire telling the Renogy when to wake up…the “ignition-on” wire. When “asleep” the Renogy doesn’t draw power from the starter battery. Some brands have a voltage sense on the main + connection, others rely on the separate “on-off” signal (ignition-on) to wake up. But what I was trying to suggest is, if it does have a 3rd wire, you DO connect it to an ignition-on signal, but ALSO have a switch on that same wire so that even if ignition is on, you can force it to remain asleep. What makes most sense to me is if the DC-DC unit has a “time-delay”, so that once you start the engine, it waits a little while before “waking up” allowing the alternator to first recharge the start battery before energy is diverted to the house battery. I presume Renogy has that built in delay, but I thought it also relied on a 3rd ignition-on wire. On my CTEK, at least the older version, doesn’t have the “3rd” wire, so I used a heavier-duty switch to shut off the “high-current” positive from the start battery. There is a delay, but I don’t know if it is “timer-based” or voltage-based…or both. Often I just leave that switch “on” so that it wakes itself up and puts itself back to sleep on its own, but I can keep it asleep with the switch. I will admit, the one burnt wire (and fuse, and switch) I’ve had in 6 years was at that switch. I don’t know if my 30amp switch failed first, or the fuse didn’t melt fast enough, or what. I replaced the switch and inline fuse and holder with similar or identical, and it’s been working since (probably just jinxed myself)…the switches are from Autozone or O’Reilly’s and were not impressive. The inline fuse was equally unimpressive, but I thought the wire gauge could handle way more than 20a.
 
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I want someone with direct Renogy experience to answer Sea’s question. I don’t have direct Renogy experience.

But what I “thought” was that there would be a “high” current positive wire, and maybe a “high” current neg (or chassis ground), which the actual charge current is passing through, but also a separate (3rd) “on-off” wire telling the Renogy when to wake up…the “ignition-on” wire. When “asleep” the Renogy doesn’t draw power from the starter battery. Some brands have a voltage sense on the main + connection, others rely on the separate “on-off” signal (ignition-on) to wake up. But what I was trying to suggest is, if it does have a 3rd wire, you DO connect it to an ignition-on signal, but ALSO have a switch on that same wire so that even if ignition is on, you can force it to remain asleep. What makes most sense to me is if the DC-DC unit has a “time-delay”, so that once you start the engine, it waits a little while before “waking up” allowing the alternator to first recharge the start battery before energy is diverted to the house battery. I presume Renogy has that built in delay, but I thought it also relied on a 3rd ignition-on wire. On my CTEK, at least the older version, doesn’t have the “3rd” wire, so I used a heavier-duty switch to shut off the “high-current” positive from the start battery. There is a delay, but I don’t know if it is “timer-based” or voltage-based…or both. Often I just leave that switch “on” so that it wakes itself up and puts itself back to sleep on its own, but I can keep it asleep with the switch. I will admit, the one burnt wire (and fuse, and switch) I’ve had in 6 years was at that switch. I don’t know if my 30amp switch failed first, or the fuse didn’t melt fast enough, or what. I replaced the switch and inline fuse and holder with similar or identical, and it’s been working since (probably just jinxed myself)…the switches are from Autozone or O’Reilly’s and were not impressive. The inline fuse was equally unimpressive, but I thought the wire gauge could handle way more than 20a.
Have a Renogy DC-DC converter; yes it has a delay before it enables the alternator voltage to start charging the house batteries. The instructions state you can run an "ignition" wire of 18 AWG to an always energized positive terminal so that the DCC knows the house voltage at all times. Yes, you should fuse and have a disconnect on that 18AWG wire. My setup is in a 2020 Ford Transit with the main positive input to the DCC connected to the Customer Connection Point (CCP) per the Ford BEM documentation with 4 AWG wire, and negative input (also 4AWG) run to the chassis ground bus near the rear doors.
 
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12vinstalls: could you expand on that? Sounds like you are saying there is no +5v requirement…but why is your panel v so low??? I thought panel voltage was supposed to be relatively high in all conditions, only current low in low light. What panel & controller are you talking about?
 
This creates voltage drop and you will never achieve full charge of the battery.
not true, its not a constant voltage drop, eventually the battery will fully charge , and then be over charged.

There is some danger of using 'cable resistance' to control charge rate as, a) there is no charge termination when the battery is full, b) there is a significant difference in charge current for a discharged and almost full battery, c) without some test equipment and skills its difficult to implement such a system safely.

a separate 20A DC/DC charger
that would be my suggestion for a 70 amp alternator, dont go any higher. Note the input current to a DD to DC charger will be higher than the output for certain battery states, say 25 amps for a 20 amp unit. There is not a lot of overhead with a 70 amp alternator perhaps producing 50 amps at engine idle speed.

Mike
 
12vinstalls: could you expand on that? Sounds like you are saying there is no +5v requirement…
The mppt doesn’t have much to act on if voltage output is close to battery voltage. Open circuit voltage in low light may actually match the label but it has not much current to offer. I meant you can still get some charge as my quoted numbers indicated in very poor light but mppt shines when it has excess voltage above battery static nominal voltage. Mppt really isn’t playing the game well until you give it two or three times battery voltage.
but why is your panel v so low???
Because the sun wasn’t really up yet. I’m 70-90V+ by 9am in clear full sun.
I thought panel voltage was supposed to be relatively high in all conditions, only current low in low light.
Open circuit voltage would probably still be 88+ volts per string, just no amps. With the ‘weight’ of the battery load it pulls the voltage down until there’s enough sun to make big volts at any reasonable amps.
There is a law in equation form that ALWAYS solves out: Watts = Volts times Amps.
Example in early sun:
90V at .1A=9W 9W @ 13V=0.69A
Later:
90V at 3.6A=324W 324W @ 13V=24.92A
Later still:
94.5V at 6.56A=620.5W 620.5W @ 14.6V=42.5A
What panel & controller are you talking about?
I have eight 100W panels 4S2P:
4 panels in Series (400W) twice; and 2 of those series strings Paralleled
I am running a 50A mppt charge controller
 
not true, its not a constant voltage drop, eventually the battery will fully charge , and then be over charged.

There is some danger of using 'cable resistance' to control charge rate as, a) there is no charge termination when the battery is full, b) there is a significant difference in charge current for a discharged and almost full battery, c) without some test equipment and skills its difficult to implement such a system safely.
The 'cable resistance' should only be used to limit the amps. I would not design a wire system for this but rather if the existing wire does limit the amps into a low battery at an acceptable level then it works fine.

I believe most alternators are dropping into the mid 13 volt range and should not present an issue. Worst case the BMS will protect while measurements are taken during initial use.
 
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