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24v battery, 24-12 40a step down buck converter, DC devices not working...

Owen Parker

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Jul 24, 2021
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I'm new at this but have a pretty solid basic understanding. Troubleshooting seems to be the weakness. Finally connected my 24v 280ah battery to the electrical system in the van. All the 120 stuff works as expected (except the transfer switch but we'll leave that to another time). Problem seems to be the 12v dc panel. Mostly. I have the usual fare, lights, usb charger, pump, 2nd fuse block, etc. Nothing is working except the pump. I tested every single device on the bench before installing in the van, so I am a tad surprised.

Basically, a fused wire runs from the lynx distributor to a 24v-12v 40A buck converter. Wires from that feed the dc panel in the distribution box. When I check the voltage at the connection point of the panel, I get 12.2v. Seems lowish, but 12v is 12v I'm surmising. I added proper DC fuses and nothing came on except the pump. Boo. I checked the power at the pos & neg posts for the usb charger and 12.2v. Hmm. I disconnected the usb charger from the panel and connected it to an external 12v power supply. Worked like a charm. Checked the power and it was 13.4v. Hmm So, device works, power getting to the panel is supposedly good. I'm stuck wondering what else to check. I'm left to guess the buck converter is tamping the volts down a tad too low, or ??? Can anyone suggest anything else to check?

If the 24-12 converter is too low, I have no idea what else to use to convert the 24v down to 12v for all my DC stuff. I'd appreciate any suggestions on alternatives as well. It is a couple grand too late to switch to 12v battery, so let's not suggest that! :)

TIA
 
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Check all your connections down stream from your DC/DC converter. Make sure they are tight. *edit* and upstream too while you’re at it. Maybe the converter is being starved of current and your 12v is output is collapsing.

Or maybe your converter is just bad? Voltage could fall flat on its face when you put any kinda load on it. The 12v devices are like nah brah that voltage is too low and won’t work but the pump don’t care none. It just spins slower.

Can you measure the output voltage of the converter while the pump is running?
 
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I use a 48v to 12v step down converter and I recall it keeping voltage pretty close to 12.3v. I believe you should be using around a 25a fuse from the Lynx to the step down's 24v input. Are you running the 12v handoff through a fused distribution block? If so, try bigger fuses. I use 25a for cigarette lighter and USB PD chargers, and 15a for everything else smaller like LED lights and fans. I recall running into issues with some devices when fuses were too small. Does your 12v distribution block also have a negative bus or are you handling that elsewhere?

What fuse size are you using for your pump? The fact that the 12v pump works leads me to believe that the step down converter is OK.
 
If voltage measures steady the only thing I believe is polarity. Main connections might be right but check right into the device.

Do you have a small 12v incandescent lamp to verify power? This will not verify polarity but will indicate voltage drop of a poor connection. Automotive test lamp is perfect.
 
Ok, I decided to connect my 12v power supply I use for testing on the bench to the dc panel pos & neg terminals. Turned off the battery completely first for safety sake. When I turned on my power supply, every damn thing came on and worked perfectly. So there's that. Checked voltage and it was 13.74v.

Fuse for the pump is 5A. Pump was running much slower before the switch. It draws 1.1A when running, so the voltage measured 12.6 when running with working p/s.

It looks like this one is definitely not working as expected although it is putting out 12.2v. I have no idea if that is how they are supposed to work or not. Should I assume I got a bad one and get another just like it? I purchased it from Amazon using a link from Will's list so I know it is supposed to work.
 
It is putting 12.2V at 1A load, but what voltage is it putting with 5A load? Like 5V :) ? Post a link to the DC to DC converter that you are using. It is either bad or by design, it is for low current.

And just to make sure there is no huge voltage drop on your wires and connections - measure both the PS output on the PS itself with the pump running and not running. Then measure the voltage with the pump running and not on the pump itself. Share the results.
 
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Ok, I decided to connect my 12v power supply I use for testing on the bench to the dc panel pos & neg terminals. Turned off the battery completely first for safety sake. When I turned on my power supply, every damn thing came on and worked perfectly. So there's that. Checked voltage and it was 13.74v.

Fuse for the pump is 5A. Pump was running much slower before the switch. It draws 1.1A when running, so the voltage measured 12.6 when running with working p/s.

It looks like this one is definitely not working as expected although it is putting out 12.2v. I have no idea if that is how they are supposed to work or not. Should I assume I got a bad one and get another just like it? I purchased it from Amazon using a link from Will's list so I know it is supposed to work.

Yeah next step would be to test another known good 12v converter.
 
Check all your connections down stream from your DC/DC converter. Make sure they are tight. *edit* and upstream too while you’re at it. Maybe the converter is being starved of current and your 12v is output is collapsing.

Or maybe your converter is just bad? Voltage could fall flat on its face when you put any kinda load on it. The 12v devices are like nah brah that voltage is too low and won’t work but the pump don’t care none. It just spins slower.

Can you measure the output voltage of the converter while the pump is running?
Voltage running into converter is 26.86v. Coming out is 12.2. I did have to use butt connecters to connect the device to the lynx distributor. I'll have to undo and redo that, but I am one of those ridiculously meticulous people, so my money is on that not being the issue, but, only one way to find out... That is the only possible wiring issue as everything else is tightened to spec...
 
It is putting 12.2V at 1A load, but what voltage is it putting with 5A load? Like 5V :) ? Post a link to the DC to DC converter that you are using. It is either bad or by design, it is for low current.

And just to make sure there is no huge voltage drop on your wires and connections - measure both the PS output on the PS itself with the pump running and not running. Then measure the voltage with the pump running and not on the pump itself. Share the results.
This is the device I am using:

I imagine I got a bad one, but the pec does not say anything more than 24v-12v 40a. I'll contact them and see about getting a new one and maybe a spare as well...
 
Reading comments, I think it is supposed to be putting out basically what it is. I'm not sure what else to purchase? Anyone have any idea?
 
The appropriately sized Victron DC/DC converter. Oh and a small 9ah battery to put on the output so handle and surges and be nice to your converter. Also has the added benefit of making the system redundant.
 
I'm almost certain you have bad wiring. Follow the instructions about measuring the voltage at the converter output and the panel output under load.

Your PS had 13.7V output with no load, the pump was drawing 1.1A and was running at 12.6V from what you said. There is likely 1V loss between your PS and the pump at 1A.
 
How about a smaller converter? Just use it to charge a small battery and let the battery handle the larger loads.
 
I'm almost certain you have bad wiring. Follow the instructions about measuring the voltage at the converter output and the panel output under load.
The converter is a very simple device. input is a wire from lynx dist. attached using butt connectors. Output is two wires using 3 way wagos. If the wiring is an issue, it is a bad butt connector. I'll definitely check that before replacing the usint.
 
Your PS had 13.7V output with no load, the pump was drawing 1.1A and was running at 12.6V from what you said. There is likely 1V loss between your PS and the pump at 1A.
 
How about a smaller converter? Just use it to charge a small battery and let the battery handle the larger loads.
Sorry Chris, but you lost me with this suggestion... You mean insert a battery and use the 12v feed to charge it and use the battery to power the DC 'stuff'?
 
use a 12v SLA battery in parallel with your DC/DC. The Victron is nice for that because you can set an appropriate float voltage.

Let’s say your lights, LEDs, USBs, and other acronyms use like 10 amps max continuous (this is just a guess) so a 15ish amp converter will be fine?

I’m just assuming your higher 12v loads are intermittent so can use the battery to bridge the current gap between your continuous loads and peak loads. Then when your loads drop the DC/DC converter pumps it’s extra current back into the battery.

And since this is in a van you could also use your alternator to keep the 12v battery charged.
 
I'm almost certain you have bad wiring. Follow the instructions about measuring the voltage at the converter output and the panel output under load.

Your PS had 13.7V output with no load, the pump was drawing 1.1A and was running at 12.6V from what you said. There is likely 1V loss between your PS and the pump at 1A.

Ah, so the voltage should NOT have changed when the pump started running? Yeah that makes sense given I was taking the measurement at the input terminals. I don't think I understand how that would help me since the input being too low to start with, but if there is a wiring issue with the pump... I think I just realized a trouble 'area'. The pump started running as soon as I added the fuse when there is an on/off switch wiring into that loop, supposedly. That is definitely something to look into LOL I'm still not sure my big problem will change, but the whole point is to test all the electrical system, so, thanks for the patience.
 
use a 12v SLA battery in parallel with your DC/DC. The Victron is nice for that because you can set an appointment float voltage.

Let’s say your lights, LEDs, USBs, and other acronyms use like 10 amps max continuous (this is just a guess) so a 15ish amp converter will be fine?

I’m just assuming your higher 12v loads are intermittent so can use the battery to bridge the current gap between your continuous loads and peak loads. Then when your loads drop the DC/DC converter pumps it’s extra current back into the battery.

And since this is in a van you could also use your alternator to keep the 12v battery charged.
Ok, Chris, I'm following. I do have a victron 12|24 dc to dc charger already. I'll have to check the total amperage. I figured 40A was going to be more than enough...
 
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