Preventing Voltage Spikes

I recently added some 12V ports to the bed so I can power a car fridge, but it looks like the fuse in the power cord for the fridge blew after the first use. I suspect that maybe the engine crank may have spiked the power; the 12v ports are connected directly to the battery. Is there anything I can install that could prevent these power spikes from happening?

 

Was the fridge plugged in before you started the truck? If so, unplug and plug it in after starting the truck.

 

yes. trying to see if there's any solution for keeping the fridge plugged in

 

I understand.

 

Youll likely need more battery reserve to not have to unplug the fridge. Theres no spikes when you fire up the truck, only dips. Lower voltage might be causing a higher current (Amps) draw and blowing the fuse.

 

I'm not an electrical engineer but I'd think a capacitor inline would keep the power constant since you have a short term reservoir of juice to steady out the voltage/current. I thought subwoofers do the same thing for the same reason essentially.

 

What is the watt rating on the fridge?
What size wire and length are you running?

Using the Volts x Amp = Watts formula, we can then properly size a setup for the wire and fuse needed. Being its a 12v, I'm going to assume its something like a 50 watt fridge?

 

This guy knows what he’s talking about.

 

When engine fires and starter is not disengaged yet, it works as unregulated alternator. For that matter all sensitive electronics shuts down briefly while engine starts to avoid damage by overvoltage.

 

I didn't know that. Hang on....I want to get my wife to see this. She calls me Mr. Smarty Pants.

 

Yeah it's a 50 watt fridge. I have 12AWG running from the battery all the way to the bed. Length is about 20 feet I'd say, at most 25 feet

 

I've seen mentions of capacitors, but how do I calculate what size capacitor I should use?

 

Be careful with a capacitor in any modern vehicle as it will introduce a voltage spike that might damage sensitive electronics.

What size fuse is blowing? Can you provide a link to the fridge? At 50 watts and 12 volts it's pulling a tad over 4 amps I assume running.

 

First off, the line needs to be properly fused really close to the battery terminal to prevent a catastrophic fire. If the fuse is far away, you have zero protection in the unfused length. Secondly, sounds like the wire size might be too small for your distance from the battery. Next, if you want to use a capacitor, you can research how a diode can be used to prevent reverse current flow. Lastly, why not just have a switch in the cab that triggers a fused relay near the battery to feed power to your auxillary outlets. Personally, I would probably buy a 12AWG exterior extension cord and chop it up to use the double insulated wire inside a flex loom to run the power and ground connection from an engine bay fused relay to the outlets. Keep the loom and wires away from high heat sources and prevent flexing & abrasion by securing along its length with plenty of black cable ties. Google image tab for 12 volt relay wiring diagram and power with inline fuse holder directly from battery post. 12v relay and inline fuse holder can be had from auto parts store or Amazon for around $15, Relay trigger switch cost just depends on your choice of switch. You really don't want to be draining your starting battery when the truck isn't running. Starting from a weak battery will lead to a prematurely destroyed starter. So, depending on your needs, a secondary battery might be a much better option.

Edit: Wire size is fine. Just read your post.

 

would a diode even help in this situation? from what i’m hearing on here it sounds like a voltage drop is causing the fridge to draw more amps causing the fuse to pop (10amp). there’s actually two fuses in place: a 10amp in line fuse at the battery (previously 40amp due to bad math) as well as a fuse inside the fridge dc cable head (10amp)

 

First, glad to hear you fused the line at the battery. Secondly, a diode will not help with your fuse blowing, only to prevent damage to sensitive electronics from reverse currents. Your best option is to use a switched relay to power the fridge with or without an auxillary battery. With the start battery only, turn off the fridge when the truck isn't running.

 

If you are using 12 AWG wire you are safe to use up to a 20 amp fuse to protect the wire from the battery to the fridge. I'd try a 15 and see if that holds. That's for solid wire. Stranded will handle more current. A diode will reduce the voltage about .7 VDC.

 

I think the problem is the fridge wire is probably like 18AWG maybe even smaller.

 

Fridge wire is 16AWG

 

Which fuse is blowing?

 

He is probably losing a bunch at the plug due to poor contacts which is causing the fuse to blow inside the cigarette lighter type plug.
The fridge really really shouldn't be drawing current from the starting battery when the truck isn't running and regardless of wire sizes or fuse ratings, nothing changes that fact.

 

I have this switch for the winch and secondary battery in bed:

$36 Blue Sea Systems 9003E e-Series Battery Switch, On/Off, Red

https://www.amazon.com/gp/product/B000MMC914 For winch the wire goes directly from this switch, for battery I have this isolator kit:

$63 Dual Battery Isolator Kit - 12 Volt 140 Amp Voltage Sensitive Relay - Complete VSR Double Battery Automatic Charger - Fits Trucks, ATV, SUV, UTV Boats and More - Safe, Water and Vibration Resistant

https://www.amazon.com/gp/product/B07N15Z5GP/ It shuts off when main battery voltage drops below secondary battery voltage. Also it allows to disable that function in emergency need when the main is dead and you need to start the engine using the secondary battery.

 

Not true of any starter with an overruning clutch in the starter drive, which has been the industry norm since way before the Tundra was ever a twinkle in Akio Toyoda‘s eye.

 

True but any permanent magnet motor will induce a voltage spike when the magnetic fields collapse.

 

Fwiw, my fridge is hard wired to the battery and I haven't had any issues. I have 4 ga wire running to a fuse block behind the rear seats for the stereo. Then I pulled a smaller than it should be wire to a 12v female "cigarette port", then plug my BougeRV into that. It was a quick wire up and try before a trip, but it's worked flawlessly for over a year so I kept running it.

What size fuse is blowing? Sorry if I missed that part

 

It was the fuse inside the plug that was blowing. To be fair, I don't really run the fridge off the starting battery when the car is off. Maybe for like a minute before I get in to start the car. I may end up just wiring in a relay; I've done so for all of the lights I set up.

 

Regardless of relay or not, those chinesium plugs have lousy current conductors and could contribute to an early death of your fridge. Good luck!

 

Bosch starter in a model year 2005 in a car brand that gen3 tries to mimic in 2024 still causes overvoltage.

 

I meant what amperage fuse is it?

 

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