12v Battery blowing fuse

[Chromdome35]

1st, I hope I'm posting this in the right forum, apologies if I'm not. I'm pretty new to all of this and have a situation that I need someone to explain to me.

I have a 12v 18ah SLA battery, showing 13.4V at the terminals.
I have a 12v load that will pull 3.3-8 amps that I want to connect to the battery.
Between the battery and the load will be.
Battery Clamps connected to what appears to be 14ga Wire (They are Battery clamps from one of my 12v battery chargers).
The wire coming from the battery clamps has an inline 10amp fuse
The wire from the battery terminates in an SAE connector.
The SAE connector plugs into another SAE Connector with 14ga wire terminated at a fuse block with each input having its own 10amp fuse. (polarity is verified correct)
From the fuse block the load is connected via 14ga wire.
Connected to the circuit between the fuse block and the load are a Voltage/Amp meter on the negative wire with a pigtail to the positive wire AND an On/Off switch on the positive rail with a pigtail to the negative wire (lighted switch).

The wiring layout described above (if i described it correctly) has been working fine when I used a 12v bench power supply, a different 12v 6ah battery, and a 20v tool battery connected via a power adapter.

When I connect the 12v 18ah battery, both 10amp fuses (1 inline right after clamps and 1 in the fuse block) blow immediately. The switch to the load is off, the only load that is receiving power is the voltage/amperage meter in the circuit.

Why would a 12v battery with no load other than a meter blow a fuse on connection to the circuit which works fine with other power sources???

 

[JeepDaddy]

What is the nature of your load? A motor (inductive), light (resistive), inverter (capacitive), etc.? You may have an inrush current issue.

 

[Bud Martin]

1st, I hope I'm posting this in the right forum, apologies if I'm not. I'm pretty new to all of this and have a situation that I need someone to explain to me.

I have a 12v 18ah SLA battery, showing 13.4V at the terminals.
I have a 12v load that will pull 3.3-8 amps that I want to connect to the battery.
Between the battery and the load will be.
Battery Clamps connected to what appears to be 14ga Wire (They are Battery clamps from one of my 12v battery chargers).
The wire coming from the battery clamps has an inline 10amp fuse
The wire from the battery terminates in an SAE connector.
The SAE connector plugs into another SAE Connector with 14ga wire terminated at a fuse block with each input having its own 10amp fuse. (polarity is verified correct)
From the fuse block the load is connected via 14ga wire.
Connected to the circuit between the fuse block and the load are a Voltage/Amp meter on the negative wire with a pigtail to the positive wire AND an On/Off switch on the positive rail with a pigtail to the negative wire (lighted switch).

The wiring layout described above (if i described it correctly) has been working fine when I used a 12v bench power supply, a different 12v 6ah battery, and a 20v tool battery connected via a power adapter.

When I connect the 12v 18ah battery, both 10amp fuses (1 inline right after clamps and 1 in the fuse block) blow immediately. The switch to the load is off, the only load that is receiving power is the voltage/amperage meter in the circuit.

Why would a 12v battery with no load other than a meter blow a fuse on connection to the circuit which works fine with other power sources???

"Why would a 12v battery with no load other than a meter blow a fuse on connection to the circuit which works fine with other power sources???"
I think you need to show us some pictures of your hookup.

 

[Chromdome35]

What is the nature of your load? A motor (inductive), light (resistive), inverter (capacitive), etc.? You may have an inrush current issue.

The load is a 24v to 12v 10A Buck Converter which is then connected to a 12v Seaflo Water Pump which pulls 3.3-8a I have been pumping water using this exact circuit. The same type meter & on off switch sit between the buck converter and the pump. I've been prototyping this design for a week and have had no issues until I tried powering it off a 12v battery via clamps.

My overall design is for a portable 12v water pump that will run off of the Milwaukee M18 and M12 batteries that I have. This is housed in a HF Apache 4800 case. I added an external SAE port so I could provide power from a Cigarette Lighter or Battery Clamps. I'm adding a couple of battery terminals so I can also connect it via jumper cables.

 

[Chromdome35]

"Why would a 12v battery with no load other than a meter blow a fuse on connection to the circuit which works fine with other power sources???"
I think you need to show us some pictures of your hookup.

I will try to get some pictures for you

 

[chrisski]

I think The water pump is the reason the fuse blows. Probably draws a bit more than 4 amps as it spins up. Also, perhaps a longer run of 14 AWG wire loses voltage causing the motor to try to pull more amperage to make up for the loss. Also, buck converters do not perfectly turn power and have some wasted power, probably adding to the draw.

 

[Chromdome35]

Here is a wiring diagram I put together to show how it's wired up.

Using a Milwaukee M18 12ah Battery, I get the following numbers with the pump turned on. The meter on the left reads the input. The switch on the left turn on the power to the buck converter. The Meter on the right displays the output from the Buck converter. The switch on the right turns the pump on.

My thought process was since I'm building this to allow a number of possible inputs, I wanted to see the incoming voltage before I turned on the buck converter. Once the buck converter is on, if the output voltage is in range, I can then turn on the pump.

This is a picture of the power input side

The two external inputs are SAE connectors in both polarities, there are also battery adapter inputs for Milwaukee M18 and M12 Batteries

From the input fuse block to the buck converter

From the Buck Converter to the output fuse block and pump

I hope this helps.

 

[Chromdome35]

Is it ok to post this in another forum with more activity? I really would like to understand what I'm doing wrong.

 

[Hedges]

Try a 12V bulb in place of the fuse (car tail lamp or head lamp.)
Open circuit, we don't expect a fuse to blow. There might be a short (light will turn on), or surge current to charge capacitor of switching supply. or supply backwards.
I wouldn't expect anything to happen with switch off. Ground goes to switch? For a light? Any chance that's hooked up wrong?

Disconnect battery, connect ohm meter instead.

 

[chrisski]

Some cheaper fuses I looked at are 12 volts, and may not take 18 volts. Looks like you only fused the 18 volt side, so perhaps these are the cheaper, less expensive fuses.

I was looking at the MAXI fuses yesterday, and some of those fuses were audio and said 12 volts only. Blade fuses in general like you’re using should be 24 volts, but that’s one of two things I can think of. I want a fuse good for both a 12 volt system and a 24 volt system, so I needed a 32 volt fuse to cover 29 or 30 volts for absorption mode. If I equalize the batteries, I will get 33 volts, so I will need to pull that fuse first.

In place of the motor, I will also recommend putting a different 12 volt load. Whether it’s a light bulb, or another low amperage 12 volt fan Should work. If the fuse does not blow, I would start to suspect the motor, either for surge current, or its bad. You could test that on a 12 volt side.

If the fuse still blows with the other 12 volt load attached, I would put another 18 volt load on. That is a little harder to find an 18 volt load, but I have a couple of RV lights that are 10 volt - 24 volts I could use. If the fuse does not blow, I would expect your DC-DC converter. Your 18 volt / 12 volt voltage and amperage seems fine.

If the fuse still blows with the 18 volt load attached, I’d suspect either a short as mentioned or perhaps the fuse itself is only rated for 12 volt.

With the Maxi fuses I was looking at yesterday, the lower voltage fuses had less metal in them in an S Pattern, and the higher voltage fuses had more metal and the pattern looked different.

 

[chrisski]

Also, the few fuse boxes I’ve done, the main input screw for negative and positive going straight to the battery. Looks like you have the voltage / current measuring device routed measuring main power than going in to the fuse box. Perhaps you can measure the from power off the fuse.

If I’m looking at your wiring correctly, the current measuring device is not-fused and if there is a short, would be a runaway.

 

[Chromdome35]

Thank you for the responses!

Since I wanted to handle multiple inputs I used the 1st fuse block in reverse so that each input would have its own fuse. Coming off the input fuse block, I didn't add another fuse as it would effectively be putting one fuse right after another, is that not the correct thinking? What would best practice be to handle this?

I tested the input block with 18v and 12v Milwaukee batteries and with a bench power supply providing variable DC Voltage and Amperage. They all worked flawlessly. The only issue I've had is when I connect the 12v 18ah battery...then a fuse blows. This is without the switch to the buck converter being on so the only load would be whatever the meter is pulling.

I checked the voltage at the battery terminals, 13.4v, and at the clamps when I attached them, 13.4v, and at SAE connecter at the end of the wire, 13.4v.

I will troubleshoot it today, using the advice offered in this thread and report back.

Again, thank you for your assistance.

 

[chrisski]

Next thing may be to bypass the switch and amp meter to the buck converter. Maybe one of those switches is bad

I was trying to understand why they meter needed two negative inputs. The meter should just need one input.

Actially as I think about it, there should be one ground wire at the switch and two red wires. The black for the common ground, a red for the light, and a red to power the load. The schematic will say for sure.

 

[Chromdome35]

Next thing may be to bypass the switch and amp meter to the buck converter. Maybe one of those switches is bad

I was trying to understand why they meter needed two negative inputs. The meter should just need one input.

Actially as I think about it, there should be one ground wire at the switch and two red wires. The black for the common ground, a red for the light, and a red to power the load. The schematic will say for sure.

The switch and the meter are visible in the 5th picture down, there are two red's and one black going into the back of the switch. The schematic for the meter shows 2 negative inputs and one positive input. I'm in the middle of my honey-do list, I'll work on this as soon as i can and report back.

This is the meter schematic

This is the meter I'm using
https://www.amazon.com/gp/product/B075V2WTT8/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

 

[Chromdome35]

Update: I went through each connection and step of the circuit with a meter to test them. Everything was fine. Then I went to Autozone and bought some quality fuses, PROBLEM SOLVED. I was using the fuses that came with the fuse block straight from China. When I swapped them out the problem disappeared.

I added a set of through-the-wall battery terminals so I could attach jumper cables to it. I also added a switched USB outlet and Cigarette Lighter Output. My thought being, if you were using a power source like a 12v battery or jumper cables, you could charge a device at the same time.

I have powered it today with the following inputs

1) Milwaukee M18 Battery (3Ah, 5Ah, 8Ah, 9Ah, and 12Ah)
2) Milwaukee M12 Battery (1.5Ah, 2Ah, 3Ah, 4Ah, and 6Ah)
3) !2v 18AH SLA Battery
4) Jackery Cigarette Lighter Output
5) My trucks Cigarette Lighter Output
6) Jump N Carry JNC 660 Jumper Cables
7) Jump N Carry Cigarette Lighter Output
8) Jumper Cables to my truck's battery

I'm going to make an SAE adapter cord to accept a connection to the Jackery 100W Solar Panel. If my understanding is correct, I should be able to pull enough power at 12v to easily power the pump.

I'm also planning on making a few more SAE adapter cables to connect to MC4, Anderson, and XT60 connectors.

I need to clean up the wiring, a few wires are too long and I need to clean up the routing. It will drive me crazy if it doesn't look neat.

Thanks, everyone for your help!

 

[Substrate]

Glad you found it. My first thought was all those SAE connections, which depending on manufacturer can be the wrong polarity, even though it looks right, so best to check the entire run of the string if you have a bunch of them together.

Example: Some guys using little Harbor Freight solar panels with clamps and sae connectors would swap to a different set of sae connectors and clamps, and suddenly found themselves in reverse polarity, even when "red to red" and "black to black" was stringently followed! I absolutely HATE sae connectors, not just because of random manufacturer polarity hookups, but also because they are piss-poor connections that get worse over time with high-resistance, corroded contacts etc and the resulting voltage drops and heat generated at those connectors.

If you can find some way to replace them, even pigtail soldering and heatshrink would be better...

Re your SLA batteries - most likely AGM's:
Have you seen any docs or printed labels on them about not exceeding a certain amount of charge current for them, like not exceeding 0.25 to 0.3C? (Which in an 18ah * 0.25C = would be about 4.5a max)

Very conveniently it so happens to be the other way around on discharge: If you try to pull more than 0.25C from them, the voltage drop is pretty bad (peukert effect in lead-acid), and your run-time will be very short, even though you may have plenty of capacity left. If your run-times are too short, and you still need to pull that type of current (you mentioned up to 8a), then I'd recommend at least an upgrade to a 35ah agm so your voltage drop won't be so bad due to Mr. Puekert.