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Old 09-20-2020, 03:15 PM   #1
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Default Renogy DC-DC 20/40/60A notes

Renogy DC-DC 20/40/60A notes

Just a few of things that can be easily missed when researching Renogy's DC-DC 20/40/60A chargers. It's all in the manual that you can download from Renogy. Feel free to correct my comments if your experience with the units prove otherwise.

#1 - LC connection - that connection is used to limit current. Charging amperage is limited to 12.5% of the rated input for the 20A and 40A models and 50% for the 60A model. The 60A model can function like a 30A model for example.

#2 - Watt rating - that's how you can figure out the max amps in at various voltages.

Max Rated Output Power:
20A model 250 watts ... 250W/20A = 12.5V
40A model 500 watts ... 500W/40A = 12.5V
60A model 750 watts ... 750W/60A = 12.5V

so at 14.4V I'd assume that means:

20A model 250 watts ... 250W/14.4V = 17.36A
40A model 500 watts ... 500W/14.4V = 34.72A
60A model 750 watts ... 750W/14.4V = 52.00A

#3 - Up to 50% greater input amperage needed (copied from manual)

Quote:
When charging converter is sending full charge, the amperage consumption will be 50% greater on the input side.
20A model : 20A + 50% = 30A
40A model : 40A + 50% = 60A
60A model : 60A + 50% = 90A

-------------------

I've looked at the specifications for several DC/DC units and for the price, I like the Renogy units (North American availability).

If LC (50% current limit) can be triggered on the fly via a switch then I'd probably get the 60A model as it would be an easy way to give the alternator a break if it's running too hot.
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Old 09-20-2020, 03:40 PM   #2
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Can they remotely be turned off by a remote dash switch, also? IMO, that would be a very, very, useful feature. If you have monitor, you would just watch the amps for AGM batteries or amps and volts for lithium and shut off all charging when the batteries got full. Would be nice to have it all in one package of current limit, on/off and output on remote. For AGM, as long a you can turn the charging off, a fixed voltage output with no timout or float would be slick as you just let it go until you see the right amps.
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Old 09-20-2020, 03:50 PM   #3
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The D+ connection turns it on/off. That would typically be connected to a point that's on when the ignition is on. A switch on that would turn it off.
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Old 09-20-2020, 03:59 PM   #4
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Originally Posted by markopolo View Post
The D+ connection turns it on/off. That would typically be connected to a point that's on when the ignition is on. A switch on that would turn it off.

Thanks, Mark, sounds like that would work for using a single alternator or a parallel twin setup, but probably not for a standalone, but on those you should be able to just disconnect the field with a switch.


We are hearing more often of people who want to add batteries or increase alternator size for older systems that would need some current limiting to prevent tripping or wire overheating so this could work well for them and provide a disconnect if wanted. A B to B would also prevent any separator closing and sucking up all the solar output. Sounds like it could be good solution to consider.
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Old 09-20-2020, 04:28 PM   #5
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Weird thought popped up.


Can you even use a B to B charger on a standalone alternator system? All the install instructions seem to show a starting battery also in the system so that would be the reference on the alternator. If you don't have that, the alternator may self destruct.
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Old 09-20-2020, 04:38 PM   #6
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Renogy units must have a battery in the circuit.

Quote:
Important Note: The Alternator will not be connected directly to the input of the DC-DC. The alternator must be integrated with the starter battery and this circuit is connected to the input starter source terminals on the DC-DC.
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Old 09-20-2020, 06:18 PM   #7
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Good info Marco. I've never understood why the low charge setting on the 20A and 40A models is only 12.5% and not 50% like their new 60A model. But then, I've never used it and don't plan to.

I have the 40A Renogy DC to DC charger. It charges at a full 40 amps (+/- 1-2 amps depending on fluctuations) so it must draw more from the alterntor to account for resistance or inefficiencies as Marco states. I thought it would be more efficient and not need to pull 50% more, but I've never attemped to measure and wouldn't know how to anyway.

The charger uses the ignition signal to turn on. I put a simple on/off switch in-line and leave it off most of the time. I mostly turn it on when leaving a boondocking situation so that my 2x100Ah lithium batteries are charged by our next stop. Usually after the engine and alternator are warmed up and we are hitting the road in ernest. I've mentioned on previous posts that if running the dash air and idling in traffic, I ocassionally noticed a voltage drop to low 12's or even high 11's voltage unless I add gas. Imediately once we're underway, voltage returns to normal range. I have the OEM single 160A alternator on my Chevy 3500 with 6.0L.
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Old 09-20-2020, 06:50 PM   #8
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Good info Marco. I've never understood why the low charge setting on the 20A and 40A models is only 12.5% and not 50% like their new 60A model. But then, I've never used it and don't plan to.

I have the 40A Renogy DC to DC charger. It charges at a full 40 amps (+/- 1-2 amps depending on fluctuations) so it must draw more from the alterntor to account for resistance or inefficiencies as Marco states. I thought it would be more efficient and not need to pull 50% more, but I've never attemped to measure and wouldn't know how to anyway.

The charger uses the ignition signal to turn on. I put a simple on/off switch in-line and leave it off most of the time. I mostly turn it on when leaving a boondocking situation so that my 2x100Ah lithium batteries are charged by our next stop. Usually after the engine and alternator are warmed up and we are hitting the road in ernest. I've mentioned on previous posts that if running the dash air and idling in traffic, I ocassionally noticed a voltage drop to low 12's or even high 11's voltage unless I add gas. Imediately once we're underway, voltage returns to normal range. I have the OEM single 160A alternator on my Chevy 3500 with 6.0L.

You may want to pick up a clamp on DC ammeter so you can check all of this kind of stuff. Just clamp around the wire so very easy. If the 50% more in than out current is correct, and you the van may be taking 30-40 with full AC running you are getting fairly high.


Your van can with a 160 amp alternator? Ours was stock with a 145 amp in 07.
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Old 09-20-2020, 09:57 PM   #9
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Quote:
Originally Posted by booster View Post
You may want to pick up a clamp on DC ammeter so you can check all of this kind of stuff. Just clamp around the wire so very easy. If the 50% more in than out current is correct, and you the van may be taking 30-40 with full AC running you are getting fairly high.


Your van can with a 160 amp alternator? Ours was stock with a 145 amp in 07.
I may ask my mechanic to check next time I have it in for service, but that's not very often with the dependable 6.0L. I get oil changed at a local quick lube that has a pit to avoid putting it on a lift.

I didn't get a sticker for my AS Avenue Suite, but one on the internet for the prior model year ('2010 chassis) said 145A. But I ran the model number on my '2011 alternator and it checked out to be the 160A model.

Better, but still just adequate.
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Old 09-20-2020, 10:03 PM   #10
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Originally Posted by rowiebowie View Post
I may ask my mechanic to check next time I have it in for service, but that's not very often with the dependable 6.0L. I get oil changed at a local quick lube that has a pit to avoid putting it on a lift.

I didn't get a sticker for my AS Avenue Suite, but one on the internet for the prior model year ('2010 chassis) said 145A. But I ran the model number on my '2011 alternator and it checked out to be the 160A model.

Better, but still just adequate.

The alternator may have been replaced also. They did show a 160 amp alternator available later for the ambulance package. Now I think they even have a 220 amp version.
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Old 09-20-2020, 10:18 PM   #11
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The alternator may have been replaced also. They did show a 160 amp alternator available later for the ambulance package. Now I think they even have a 220 amp version.
I always assumed my alternator was original, but I bought my rig used (5 yrs. old) so who knows. I would definitely look into the 220 amp if I needed to replace. Any negatives to go to the next size bigger alternator if I'm not going to tax it any more than my present one?
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Old 09-27-2020, 06:42 PM   #12
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I am curious if anyone knows, can you just use any cheap Chinese solar controller as a DC-DC charger? Don't they take whatever power they can get in (under their limit) and then provide that to the battery they are designed to charge? Are they not a TON cheaper than Renogy?
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Old 09-27-2020, 08:27 PM   #13
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Originally Posted by israndy View Post
I am curious if anyone knows, can you just use any cheap Chinese solar controller as a DC-DC charger? Don't they take whatever power they can get in (under their limit) and then provide that to the battery they are designed to charge? Are they not a TON cheaper than Renogy?
I don't think so. Renogy now makes some combined solar controller/DC to DC chargers, but again the cost is $250-$300. I don't see how a solar controller can do two completely different things unless the combined components are built into the product.
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Old 09-27-2020, 08:41 PM   #14
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Just because they sell a box that combines both functions doesn't mean that they don't use the same components. If a solar controller takes 14 volts from the alternator and outputs a controlled charging current for your defined battery that would be a DC to DC charger I am pretty sure.

I don't know of any cheap 60 amp solar chargers and if you have a 200 amp alternator you will probably wanna get a big chunk of that into your lithiums. I was originally inspired by a guy who used a 120v inverter to power his RVs charger while driving to isolate the two sides so his chassis and coach batteries didn't see the same charge profile when they were different kinds of batteries.

I am more thinking about limiting the amount of current sent to my lithium pack when it's hungry. Don't wanna burn up my RVs 120 amp alternator, I can always plug it in or let it charge off solar. If I do find myself in a situation where I am regularly in need of filling the battery during a day of driving I'll look into a 2nd alternator. For now I just want things to proceed as they always have only with a battery that I will have for decades instead of years and I have a bunch of cheap chargers from various solar projects.
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Old 09-27-2020, 08:50 PM   #15
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Just because they sell a box that combines both functions doesn't mean that they don't use the same components. If a solar controller takes 14 volts from the alternator and outputs a controlled charging current for your defined battery that would be a DC to DC charger I am pretty sure.

I don't know of any cheap 60 amp solar chargers and if you have a 200 amp alternator you will probably wanna get a big chunk of that into your lithiums.

I am more thinking about limiting the amount of current sent to my lithium pack when it's hungry. Don't wanna burn up my RVs 120 amp alternator, I can always plug it in or let it charge off solar. If I do find myself in a situation where I am regularly in need of filling the battery during a day of driving I'll look into a 2nd alternator. For now I just want things to proceed as they always have only with a battery that I will have for decades instead of years and I have a bunch of cheap chargers from various solar projects.

This has come up several times in the past, and I think the best reason that I have heard is that solar panels generate very clean 12v, or higher, power while alternators can often have 6-10% or more ripple on the DC. The electronics need to be designed to handle that kind of power and solar controllers aren't.


If you are looking to limit current, the solar controller won't do it anyway. It will just burn up if you send it more than rated power.


A B to B charger, limiting split charge relay, smart alternator is needed to limit the current from the alternator, which certainly is a good thing to do IMO.
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Old 09-27-2020, 08:51 PM   #16
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"If a solar controller takes 14 volts from the alternator and outputs a controlled charging current for your defined battery that would be a DC to DC charger I am pretty sure."

What am I missing here? Whenever does a solar controller interact with an alternator? Other than not allowing current to back flow into solar panels.
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Old 09-27-2020, 08:58 PM   #17
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Got it Booster, so they are not isolated and will simply burn up if hooked from the chassis circuit to the coach circuit when the coach battery needs to be charged. That's what I was asking. Saved me burning up one of my spare solar controllers.

Perhaps I'll go back to putting one of my cheap inverters onto the power coming from the chassis to power my coach's converter.

Rowie, I was asking about using a solar controller as a DC-DC controller, read back a few messages
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Old 09-27-2020, 09:31 PM   #18
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Originally Posted by markopolo View Post
If LC (50% current limit) can be triggered on the fly via a switch then I'd probably get the 60A model as it would be an easy way to give the alternator a break if it's running too hot.
An alternate solution might be the Battle Born Lithium Isolation manager:

https://www.amazon.com/Battle-Born-B.../dp/B07DY8S815

This will let the battery take full power from your alternator for 15 minutes and then disconnect for 20. This way the manager will see if the resting voltage indicates the lithium battery is charged. If not it reconnects the battery to your chassis electrical system. Always watching that the voltage isn't too much for the lithium battery or too little indicating the alternator isn't keeping up.
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Old 09-27-2020, 10:07 PM   #19
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An alternate solution might be the Battle Born Lithium Isolation manager:

https://www.amazon.com/Battle-Born-B.../dp/B07DY8S815

This will let the battery take full power from your alternator for 15 minutes and then disconnect for 20. This way the manager will see if the resting voltage indicates the lithium battery is charged. If not it reconnects the battery to your chassis electrical system. Always watching that the voltage isn't too much for the lithium battery or too little indicating the alternator isn't keeping up.

Personally, I am not a fan of thermal cycling electronics off a high limit, which is really what this would do, I think. Thermal cycles are much harder on things than just turning them down to what they can handle without getting too hot. You will net just about the same amount of power, based on what the Balmar gets when cycling. When you are on a single alternator, it isn't good to abuse it unless you carry a spare, IMO.
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Old 09-29-2020, 11:45 AM   #20
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If in Canada the price for the 20A & 40A models on Amazon.ca isn't too bad right now.

20A CDN$129.99
40A CDN$179.99
60A CDN$249.99

Looks to be taxes included & free Prime shipping.

Given that these units are boost/buck (step up/step down) the 40A probably meets the needs of most people that have single stock alternator equipped vans. The 40A might put as much as a 60A load on the system (according to the manual). The 60A might put as much as a 90A load on the system so maybe too much for several hours continuous run time.
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