DC-DC charger current limiting

[sunrise]

Hi folks,
I recently installed a Victron Orion-Tr 12/12-18 DC-DC smart charger on my travel trailer. it's connected to TV (SUV) via 7pin trailer cable and the fuse in the TV is 20A - that's why I purchased the 18a charger - I do not want the charger to draw too much current that trip the fuse.
Well, that didn't work, it already trip the fuse several times - it turned out the 18a is just that the charger will be able to put out 18a continuously, I did a bit more research on this and found that the charger could draw 25A for a brief amount of time (~10s), enough to trip the fuse. So for now I had to go to charger settings to lower the absorption voltage from 14.4 to like 13.6, to limit the current, but this only works if the battery still has enough juice in it, if it is nearly fully discharged then the voltage difference would still cause a current too high.
Is there any inline device that I can use to limit the current? seems like it's going to be hard to find a resistor rated at 15a, plus it's probably going to generate a lot of heat. I do not want a separate wire from the alternator, It's a mid-size SUV and it's very hard to run wires from alternator to hitch. I would be pretty happy to have a 12-15amp charging current.

Thanks in advance.

 

[geoffire]

I'd reach out to Victron. That unit might have a constant current mode when the battery is very low so so if you add an inline resistor or whatever it will still push the same current.

 

[grizzzman]

Fuses are generally rated at 1.25 IE 25 amps with time as a factor. My bet is the 25 amps is much longer than 10 sec. Why not upgrade the wiring to take advantage of the units capability?

 

[sunrise]

Fuses are generally rated at 1.25 IE 25 amps with time as a factor. My bet is the 25 amps is much longer than 10 sec. Why not upgrade the wiring to take advantage of the units capability?

DC/DC charging isn't going to be my main source of charging, I have Converter for shore power charging @50a, and 250w (rooftop) + 120w(portable) solar. I need dc/dc charging during raining days and night time, so the fridge isn't going to drain the battery.

Upgrading wire is just a lot of hassle(running additional wires on both my TV and Trailer), and it's also an additional step (plug) every time I hitch and unhitch.

 

[sunrise]

Fuses are generally rated at 1.25 IE 25 amps with time as a factor. My bet is the 25 amps is much longer than 10 sec. Why not upgrade the wiring to take advantage of the units capability?

It's definitely less than 10s, I was looking at the Victron app while I turn on the running light (triggers charger on) I think the fuse was blown in like 3 seconds, So it's probably higher than 25a? Or the fuse was underrated? I bought a box of assorted ones from amazon.

 

[sunrise]

I'd reach out to Victron. That unit might have a constant current mode when the battery is very low so so if you add an inline resistor or whatever it will still push the same current.

That's a good point. likely.

 

[sunrise]

Do you guys think putting this between fuse and DC-DC charger would limit the current to 15A?

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[Bud Martin]

So there is no setting for Victron to set the maximum charging current?

 

[sunrise]

So there is no setting for Victron to set the maximum charging current?

Nope, you can set absorption and float voltages, but the current is also affected by SOC

 

[Bud Martin]

my MPP solar I can set what the maximum charging current will be limited to from 10A all the way to 80A, so if my SOC is at about 10% (12V) the charging current I can set it to what I want if I do not want fast charging.

 

[geoffire]

Running another wire really isn't that difficult, but if you really don't want to you could just install a slightly larger fuse (25A?). I'm a little surprised you can't program a lower output, but I guess at that price point...

I believe those units have a DC-DC boost converter for when the input voltage is lower than needed for the desired 18A output. So, the lower the input voltage the more amps it will draw to supply the desired output. Does this vehicle happen to have a "smart" alternator? If so in many cases your system voltage will dip down pretty low. I don't know how the unit behaves then, but it might still be trying to provide 18A at 13.6V or whatever (244w) - if the input is say 11V. That's 22.25A + whatever inefficiencies (maybe as low as 80%), so that's a plausible (but very much worst case estimate) 27.8A right there.

That unit does have an enable pin, I'm sure there's a way to rig something up so if the voltage drops below a certain level to disable the device. Well hell, if you're doing that you could just monitor current directly and do the same. Honestly I'd just put in a 25A fuse and go about my business.

 

[sunrise]

Running another wire really isn't that difficult, but if you really don't want to you could just install a slightly larger fuse (25A?). I'm a little surprised you can't program a lower output, but I guess at that price point...

I believe those units have a DC-DC boost converter for when the input voltage is lower than needed for the desired 18A output. So, the lower the input voltage the more amps it will draw to supply the desired output. Does this vehicle happen to have a "smart" alternator? If so in many cases your system voltage will dip down pretty low. I don't know how the unit behaves then, but it might still be trying to provide 18A at 13.6V or whatever (244w) - if the input is say 11V. That's 22.25A + whatever inefficiencies (maybe as low as 80%), so that's a plausible (but very much worst case estimate) 27.8A right there.

That unit does have an enable pin, I'm sure there's a way to rig something up so if the voltage drops below a certain level to disable the device. Well hell, if you're doing that you could just monitor current directly and do the same. Honestly I'd just put in a 25A fuse and go about my business.

I can't say the 25a fuse thing didn't cross my mind, especially when I have a box of them right there, I didn't do it because in the fusebox there are so many thin wires bundled together enter and exit the fuse box, I am worried if the charging wire overheated and melt the insulation of itself and some other wires, it might cause serious and hard to fix damage of my TV.

 

[mikefitz]

The Victron 12 12 18, will attempt to maintain the output at 18 amps in the bulk stage. Due to inefficiency and the voltage drop along the supply path from the vehicle battery/alternator, the input current to the Victron will be higher to compensate for these losses. The only safe and reliable solution is to add a suitable fuse at the battery and run an additional suitable rated cable cable to the connection point. The additional cable could replace, or be added to, the existing cable to the trailer connector on the vehicle
This will not be a problem for a vehicle electrical technician or a reasonably skilled DIY.

Mike

 

[HaldorEE]

The Victron 12 12 18, will attempt to maintain the output at 18 amps in the bulk stage. Due to inefficiency and the voltage drop along the supply path from the vehicle battery/alternator, the input current to the Victron will be higher to compensate for these losses. The only safe and reliable solution is to add a suitable fuse at the battery and run an additional suitable rated cable cable to the connection point. The additional cable could replace, or be added to, the existing cable to the trailer connector on the vehicle
This will not be a problem for a vehicle electrical technician or a reasonably skilled DIY.

Mike

I just assumed the Orion-TR Smart would be as configurable as other Victron equipment. I am a bit troubled by this.

It has BlueTooth for configuration, but can't be controlled by a BMV-712 wireless Victron.Connect.

There is no way to control the max charging amps or the max input amps. It seems like a step back in functionality compared to the Victron MPPT Smart Chargers which makes no sense. The Orion-TR Smart is a newer design than the MPPT.

Victron better step up their game. My invert/charger, solar charger and battery monitor are all Victron, but I haven't got the DC-DC controller yet. I may hold off on getting that part and take another look at alternatives. Victron could fix this with a firmware update. I hope they do so soon.

 

[LandLocked]

The manual for the Orion-TR Smart DC-DC Charger (Section 5.1) shows that this product has a complicated behavior that can't be understood from the specs along. After studying Figure 8 for a while, I think this charger does have some ability to throttle the input current---demonstrated by the sloping portion of the Icharge (purple) plot (between times "2" and "3"). The caption describes that ramp down of Icharge as:

2 → 3: If VIN ≤ Vshutdown, the charge current will be reduced to prevent VIN to drop below Vshutdown.

Victron designed this feature in the context of "engine shutdown detection", rather than to address large voltage drop in the input cabling. But, I wonder if appropriate settings of the parameters in Figure 8 might possibly allow this charger to throttle input current in the OP's situation.

I have been looking for a DC/DC charger with the ability to directly adjust the maximum input current, but I have not found such a device.

 

[LandLocked]

A sentence on page 10 of that manual is interesting:

As seen in “engine shutdown detection sequence 1→3”, VIN will be lowered by Vcable. When the alternator voltage drops fast (smart alternator) the charge-control needs some time to reduce charge current and keep VIN at Vshutdown.

I wonder if the OP's fuse is blowing immediately after the Orion turns on (at max power), before the Orion has time to throttle its input current. Perhaps a slow-blow fuse on the input circuit (TV's trailer power circuit) would give the Orion time to throttle?

 

[RyG]

A little late to the game, but I too want to know when Victron will make this presumably software-only upgrade.
When charging from my alternator, I need to limit the current more than when charging from shore power. I do this by putting the unit in "power supply" mode and manually setting the voltage to limit the current seen through the shunt. This is obviously an iterative process to keep an eye on the current and then manually upping the voltage to eventually reach 100% SOC.

 

[Short_Shot]

This is an interesting post.

First, I agree that it would be nice if the victron unit could limit current to a user configurable value. I don't know if the hardware can do so though.

Second,

Funny that I had a guy insisting left right and sideways that this charger doesn't do exactly this and yet here is someone else showing it. Wish I'd found this post then.

Unfortunately the factory wiring in most vehicles is explicitly designed to cause a voltage drop to artificially limit the amount of current going to a trailer.

It's only designed for minimal maintenance charging and is usually grossly undersized for anything more than 5-10 amps, and as you've seen this 18a charger will draw much more than 18 amps because of the voltage drop it causes.

With a lead acid battery this voltage drop is no problem. I normally see a maximum of 8-9 amps with a low battery and rather soon it settles down to only 1-2 amps, depending on my alternators current output. This of course is safe for the wiring.

I suspect a similar current limiting effect will occur with the lithium battery but I haven't had a chance to test it.

I'm pleased to see you measured 25a too, because I recall figuring that would be roughly my expected draw with my undersized factory tow wiring.

 

[A.Justice]

My Renogy 40a DC/DC pulls ~52a on the input side from a 12v source. At first I thought it was horrible inefficiency, but I realized it was stepping 12v up to 14.4v, which is ~18% higher, and causes (ignoring inevitable voltage drop) an ~18% increase on input power draw.

My DC to DC charger is inches from the 12 volt power source as well. So I have very little voltage drop. I imagine if the charger is in a trailer, The voltage drop will be much more extreme, especially with the small wiring on top of step-up losses. There is also a DC surge from the input side when the charger is turned on, it spikes to 65a ( which is an additional 22% more power, for a total of 40% more than the rated charging load).

An 18 amp charger + about a 20% loss between step-up and voltage drop = ~22a pulled from the battery. I would plan your wiring and fuses for around 30a (slow blow to protect against the 40% overpower brief surge), which leaves a margin of safety.

There's no way you're going to be able to power that through your existing 7 pin.

 

[Short_Shot]

My Renogy 40a DC/DC pulls ~52a on the input side from a 12v source. At first I thought it was horrible inefficiency, but I realized it was stepping 12v up to 14.4v, which is ~18% higher, and causes (ignoring inevitable voltage drop) an ~18% increase on input power draw.

My DC to DC charger is inches from the 12 volt power source as well. So I have very little voltage drop. I imagine if the charger is in a trailer, The voltage drop will be much more extreme, especially with the small wiring on top of step-up losses. There is also a DC surge from the input side when the charger is turned on, it spikes to 65a ( which is an additional 22% more power, for a total of 40% more than the rated charging load).

An 18 amp charger + about a 20% loss between step-up and voltage drop = ~22a pulled from the battery. I would plan your wiring and fuses for around 30a (slow blow to protect against the 40% overpower brief surge), which leaves a margin of safety.

There's no way you're going to be able to power that through your existing 7 pin.

Man.

After the way that other guy berated me (in another thread about this) you'd think all of us are wrong about how these pull more current than they put into the charge side because ohms law and stuff.

I'm feeling real smug right now.