# 100 watts from your cigarette lighter?

Discussion in 'Amateur Radio News' started by WJ6F, Jul 29, 2020.

1. ### WJ6FHam MemberQRZ Page

Since I have already done a few videos on mobile installs I thought I would throw this one in too. The MFJ-4403 Transceiver Voltage Conditioner! The MFJ-4403 Voltage ConditionerIs a pretty amazing item in that it not only protects your radio, but it will also allow you to plug into a cigarette lighter and run your radio at 100 watts SSB! The MFJ-4403 has six 4.16 Farad capacitors and blade fuses at the input and output. In this video I show that you can in fact use the MFJ-4403 Voltage Conditioner to make a contact using 100watts while plugged into a cigarette lighter.

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2. ### KC8UDHam MemberQRZ Page

I've been running my Icom IC-706 for years through a cigarette lighter plug with no problems since I replaced the 10 amp fuse in the fuse box with a 20 amp fuse. Used to blow the 10 amp fuses when the radio was up to full power.

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3. ### WA6JJMHam MemberQRZ Page

Have you tried the voltage conditioner at 100 watts on cw??

4. ### PA0MHSXML SubscriberQRZ Page

Let's do some math here. The energy stored in a capacitor is 0.5 * C * V * V. So at 13.5V, these caps store roughly 1500 Joule which equals 1500 Ws. This sounds like a lot of energy and it is. However, suppose they charge up to 13.5V and under full load, the voltage at the cigarette lighter socket drops to 12V. In that situation, the caps only "bridge" the drop from 13.5V to 12V. That's 1.5V.
The amount of energy used from the caps is then 18J or 18Ws. 18 Watt during one second. Or 100W during 0.18 second. That begs the question if that device does anything at all but drain your wallet.

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5. ### W0PVHam MemberQRZ Page

TWENTY FIVE FARADS! Holy cow, thats a lot of short term energy storage in such a small box!

Today few cars are equipped with actual cigar-lighters. Instead they have "accessory power outlets" and there is a slight but significant mechanical difference in the respective sockets, depth spec of plug center pole, etc.

In theory this makes a cigar-lighter socket work with either a heating element or an accessory plug, but a cigar-lighting heater ought not activate if inadvertaently plugged into an accessory socket unless pushed in really hard which can be a safety issue as accessory sockets may not be designed to handle the heat load (plastic).

The amp capacity of a modern socket varies too. My Mazda accessory socket is fused at only 10 amps. My old Thunderbird cigar-lighter socket was much more. But the problem plugging a 100w radio into either is not ampacity, but VOLTAGE DROP.

At low load there was 12v at the socket. Receiving and QRP rigs can work just fine. But with more QRO, at instantaneous peak loads, > 10a / 100w input, this could drop to less than 10v. The wire guage, intermediate connectors, etc, for an accessory socket, are just too wimpy.

This voltage drop can cause bizarre reactions in many rigs. Distorted audio, if not outright just shut off or power cycling. Serious damage could probably occur if prolonged. Plus that conducted high peak load power distortion can propagate throughout the vehicle to other devices and systems causing dimming lights or even other much worse weird problems, engine or brake electronics malfunctions.

Large capacitance banks have been commonly applied for years in automotive high-end audio installations. Sometimes called "stiffening caps" they provide isolation and peak power capability for outboard power amps that supply bass woofer speakers, often remotely mounted under seats or in the trunk, which is a long wire run from the primary power source battery / alternator.

Certainly its best to add a large gauge wire power feed directly from the battery post into the cabin or trunk for QRO radios / amps, but this is impractical for RENTALS. When flying and renting a car I like to take a small HF rig along with a triple-mag mount and a fist-full of Hamsticks or little Hustler whips. And with poor propagation today, the five watts of a FT-817 alone just doesn't hack it, bring the lite IC-7300.

Expecially for enabling that to work better, this nicely packaged little MFJ unit seems like a good deal.

73, John, WØPV

Last edited: Jul 30, 2020
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6. ### KC4LRRXML SubscriberQRZ Page

I used one for a while. It worked well on eliminating ignition noise.
Stay Safe,
RJ
KC4LRR

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7. ### KF5LJWHam MemberQRZ Page

This kind of crap gives ham radio operators a really bad name. This is exactly why pros consider hams CB operators. They have no clue what they are doing.

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8. ### GM0UOUHam MemberQRZ Page

Sounds good KC
GMOUOU

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9. ### AC0GTHam MemberQRZ Page

I wonder how this compares to something far cheaper, like this from Powerwerx: https://powerwerx.com/dc-line-noise-filter-powerpole-connectors

The MFJ voltage conditioner can claim handling higher power, polarity protection, fuses, and a few other bits but I can buy 3 or 4 of those noise filters from Powerwerx for the same price. With Powerpole plugs there should not be any swapping of polarity. Assuming the car socket, the radio cord, or any other bits between the radio and battery have the correct fuses then the fuses and lights in the MFJ box adds nothing.

If someone wants polarity checking then there's a cheap and quick fix for that too: https://powerwerx.com/testbuddy-powerpole-led-polarity-tester

This looks like a relatively large and expensive box for what it does. If it had more Powerpole outputs, perhaps another switch to power up the outputs separately, a volt meter, breakers instead of fuses, and/or whatever, then it might be something I'd consider even if it cost a bit more.

10. ### K3XRHam MemberQRZ Page

The 20 amp fuse is great if the wire can take it without melting down. There may be some but I've never encountered a lighter plug that was fused higher than 10 amps. Do you suppose there's a reason for that?

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