Mailbag October 2024 special mailbag item

Today a special mailbag post about a product that i received today (oct2024) :

It was delivered by a company i heard of just a few days ago when i received an email containing
"We are glad to inform you that VANGUARD LOGISTICA has entrusted us, Nacex Internacional, with the delivery of your parcel."

The package was send as a gift yo me from Spain. For some year i am a happy customer of  "Openbank" a bank based in Spain where you can a have bank account that not only gives an interesting savings account interest rate, you also don't need to pay a monthly fee for your account.

With the debit card you can pay in most countries worldwide or withdraw cash from an ATM (on the internet you can indicate in what counties the card will work). And sometimes you can also win prizes (e.g. by using your bank card [ https://www.openbank.nl/acties ] ). A disadvantage of this bank account is that using iDeal is not (yet) possible and money transfer with a dutch bank normally takes around a half (work) day.

Several days ago i was contacted by the Openbank that i had won a free Sony WH-1000XM5 headset .

At first i did not believe that hat bank had contacted me  so i contacted them using the contact information i had from the bank to verify the message. And yes it was true, i was one of the (if i remember well 27) winners that had won this expensive headset.

And today i received my  WH-1000XM5  ( For more info about this headset see e.g. https://tweakers.net/pricewatch/1815448/sony-wh-1000xm5-zwart.html )

Here some more photos:

Mailbag September 2024 -Part2- DVI video connection for the FT710

This Mailbag September 2024 part-2- blogpost is a combination of a mailbag video and info about the FT710 video output. (Yes i know i published this 7th of October, i have little backlog in my mailbag postings.)
The Yaesu FT710 has a small touchscreen. One of the nice features of the FT710 is that also a monitor can be connected using DVI-D cable to display this screen. There are also report from FT710 users that use an DVI-D to other video format cable. However this is not recommended by Yaesu as it can damage the FT710 (Also a mouse can be connected via USB)
I already use a monitor (via HDMI and a HDMI switch) for my laptop a Raspberry PI and other devices that also has an (unused) DVI-D input.

	In a local shop i found a DIV cable for 2.50 euros/ So i did buy it. However... This was not the right DVI cable. The four pins next to the horizontal pin should not be there .........
	DVI-D cable from china (AliExpress)
	This is the correct DVI-D connection (AliExpress cable above)
	For my FT710 a cheap  simple computer USB mouse (less than 2 Euro at the Action in The Netherlands).

And the result...
I can (also) display the Yaesu FT710 screen on my monitor screen.

Using the Monitor input selector switch (on my monitor) and a small HDMI switch i can select between different devices that can be shown on the monitor:

Monitor Input Selector	HDMI switch	Device selected
VGA	-	(currently) nothing connected
DVI	-	Yaesu FT710
HDMI	Input 1	Laptop
HDMI	Input 2	Raspberry Pi

When the laptop is not selected i can still see the screen of my laptop itself that i normally use as my secondary screen (when on my desk connected to the monitor). The screen of the Yaesu FT710 is always visible on the Yaesu FT710 device itself and big on my monitor screen when selected.
(For the mouse on the Yaesu FT710 i use a separate second mouse.)

Mailbag September 2024 -Part1- Yaesu FT710

Almost end of September. Time for my September mailbag posts, that will be divided in several parts. (and some will come in October) This is Part1 about the Yaesu FT710 Radio - Tranceiver.

	FT710 AESS Tranceiver Only the packaging will be shown in this blogpost.  For those who want to see the device itself, there are many pictures and YouTube videos on the internet.  I expect i will make other blogpost whowing more of this device.
	Some additional items for the Yaesu FT710
	The power supply that i did buy for the Yaesu FT710
	Antenna switch. Not really needed to use this device. However i liked it very much as this switch allows to select between multiple antenna's and multiple tranceivers. (Also a dummy load , VNA or (SDR)radios can be easy selected when connected.
	A monitor ( With DVI-D connector) can also be connected to the Yaesu FT710 . I already had a monitor with this input. More about this in the next mailbag blogpost.

Mailbag August 2024

August 2024 has not finished yet and i am still expecting some items!
However i already want to publish this mailbag post.
This time the items came from Amazon, (not from Aliexpress )

	Book SDR Software Defined Radio
	Book radiotoday guide to the  Yaesu FT710
s s	Screenprotectors for a Yaesu FT710 radio

Testing Outdoor 2 meter Antenna

This is a 2 meter antenna i have temporary mounted outside for testing purposes. It is connected to long thin coax cable. With the coax-cable i can reach the vna connected to my computer. So i included it in the series of quick antenna tests.

See below the result:

Testing RH770 Antenna

 Also from AliExpress i got this RH770 Antenna

The length is adjustable so it is possible to do some tuning.

I did test it on full length.

Testing Abree AR771 Antenna

I also have 2 Abree AR771 Antenna's from AliExpress

They both look the same. See picture above. (Perhaps it are fake clones). Below the results of these two antenna's.

Testing another Aliexpress Antenna

Below the results of the measurement of another Antenna. 

I did buy this antenna some time ago on AliExpress.

Testing Quansheng Antenna

When testing the gate fence antenna (see a previous post) i also wanted to compare the measured result with some other antenna's. This is the result of a quick measurement of an antenna that came with of one of my Quansheng 2m/70cm radio's.

Gate fence electronics dismantling -2- Testing gate fence antenna

Testing a gate fence antenna with a vector network analyzer. This is a picture of the antenna of the original receiver for the fence controller after some cleaning. ( See previous blogpost)

As i have a vector network analyzer (vna) i wanted to test the antenna to check on what frequencies it can be (re)used. I soldered an sma connector to the coax wire, calibrated the vna and did a quick scan over a relative broad range.

See below the results displaying Smith chart, Quality factor and swr (VSWR). The lower the swr the better. The minima in the swr curve give an indication of optimal frequencies.

I also did the same quick scan on some other antenna's and post the blog reports with the results.  Therefore this blogpost is in fact part of two different series of blog posts.

-1- Dismantling the electronics of a gate fence. ( #GateFence )
-2- Some antenna's quick tested ( with a vector network analyzer (vna) ).

Gate fence electronics dismantling -1- Main control and rx board

In this post some pictures of electronics in a 220 Volt gate controller to control 220 Volt motors.After many years of service this device was not working reliable anymore and i needed to replace it. This blogpost is also to document the old situation.

Top left you see a transformer top right are battery holders (not used) . In the middle of the picture you see the main controller board. Also you  can see a part of the antenna. However this remote control was not used.

The cable bundle on the right form a separate circuit with cables going to a light sensor for a lamp.

In this picture the mains to the control board is disconnected .(The wires where temporary placed in additional screw terminals connected to nothing to put the fence control temporary out of service).

Original the connection was to the left two connections where also the white wire on the left is connected. The white wire is to power a 433 MHz remote control switch box (bottom left). From this control box go wires to contacts on the main controller board to external contact to open and close the gate. Below a closeup of the control board after disassembling.

On the right is the connector for the receive module. Below some pictures of this module.

As already mentioned the control board is completely replaced with a new (different) board. I also removed the antenna and tested it with a vector network analyzer. You can see the bottom part of the antenna in the first picture of this post top right.
Results of antenna measurements will come in a next blogpost.

Measuring Resistance of Fuses with a Milliohm Meter and Kelvin Clips -4- (Self Resettable fuse )

Recently i received this 30A self resettable fuse via AliExpress.

As you can see on the pictures on one side is printed:

A                        (i don't know yet what this means)

Suppl. Prot. 
LINE  LOAD (to mark te connections).

On the other side of the self resettable fuse has the tekst

ZHONGZUI 78 Series 30A
125/250 VAC 50/60 Hz  50VDC 
TC3OL1/U3

And symbols suggesting that the fuse had passed some tests.

And yes i tested it with my Milliohm meter by connecting the Kelvin Clips.

The measured resistance was only 0.002 Ohm

I don't know what the resistance will be under normal use contions, however is was happy surprised with this low resistance !! 

Measuring Resistance of Fuses with a Milliohm Meter and Kelvin Clips -3- (More 12 Volt Fuses)

I received more 12 fuses and in this this blogpost i am going to present the results of the 12 Volt fuses. My intention was to publish after my post about the 250V glass fuses some evaluation of the data. However i received from Aliexpress a nice Anderson Powerpole connection block "DC 36V AP-8S 8 Channel Power Distributor For HF Radio Communication Power Supply Splitter Anderson Powerpole Screw Fixing" with more 12 Volt fuses. 

As i only had a few results of 12V fuses in my first post about the car fuses and i was curious about these Chinese fuses i gave more priority to measure the 12V fuses.

I want to do a separate blogpost about a review of this Anderson Powerpole block (and it also will appear in a mailbag blog) as i think it is a real nice power block that i bought for a decent price.  Not only does did it had a set of fuses in the block, also a spare set of fuses was included. 
So i now additional have 2 x ( 1x 40A + 3x 25A + 2x 15A + 1x 10A + 1x 5A ) fuses.

In the table below are also the results from the set car fuses already mentioned in the previous blog about the 12 V car fuses (= S1 [set1] ) and the fuse that came with the single fuse holder (= H1) . 

The measurement with this single fuse holder are not included as i wanted to focus this post on the fuse not on the fuse holder(s). 

Resettable Fuse Circuit Breaker

Via Aliexpress i also got a 12V 24V DC Car Truck Audio Resettable Fuse Circuit Breaker 30A Circuit Breaker. (see picture below) 

Resettable Fuse Circuit Breaker

A nice thing about this fuse is that you can reset it and it can be used as circuit breaker. ('Resettable Fuse Circuit Breaker'). I was curious about this fuse so i ordered one and included the result in the table below.  Pressing the circuit breaker and resetting the fuse (several times) gave each time the same resistance.
Spoiler alert: Relative to the other 30A fuse the resistance seems higher. However the resistance is still low.

Safety

Be aware that these resetable fuse circuit breakers (and also the normal 12V car fuses from AliExpress) have a bad reputation and can be unsafe.

The Carpoint fuses that i did buy at the Gamma  in The Netherlands are also made in China. (See packaging bottom right). 

Measurement

I removed fuses (one by one) from the Anderson Powerpole block and measured the resistances ( Ab to Ab7 [the number corresponds with the number on the Anderson Powerpole block ] ). I was a little difficult to remove these fuses. 

The spare fuses that came with the Anderson Powerpole block ( Ax to Ax7 ) where also measured.

The results

Table 1: Results 12V fuses (Including previous results, sorted on rated current). 

Fuse	Color	Rated Current	Measured Resistance	Calculated Voltage drop at 100 mA	Calculated Voltage drop at rated current	Calculated Voltage drop at rated current in % relative to 12 Volt
Ab7	Biege	5	0.014	0.0014	0.070	0.58%
Ax7	Biege	5	0.013	0.0013	0.065	0.54%
S1	Brown	7.5	0.009	0.0009	0.068	0.56%
Ab6	Red	10	0.006	0.0006	0.060	0.50%
Ax6	Red	10	0.006	0.0006	0.060	0.50%
H1	Red	10	0.007	0.0007	0.070	0.58%
S1	Red	10	0.006	0.0006	0.060	0.50%
Ab4	Blue	15	0.004	0.0004	0.060	0.50%
Ab5	Blue	15	0.004	0.0004	0.060	0.50%
Ax4	Blue	15	0.005	0.0005	0.075	0.63%
Ax5	Blue	15	0.005	0.0005	0.075	0.63%
S1	Blue	15	0.004	0.0004	0.060	0.50%
S1	Yellow	20	0.003	0.0003	0.060	0.50%
Ab1	Clear	25	0.002	0.0002	0.050	0.42%
Ab2	Clear	25	0.003	0.0003	0.075	0.63%
Ab3	Clear	25	0.003	0.0003	0.075	0.63%
Ax1	Clear	25	0.003	0.0003	0.075	0.63%
Ax2	Clear	25	0.003	0.0003	0.075	0.63%
Ax3	Clear	25	0.003	0.0003	0.075	0.63%
S1	Clear	25	0.002	0.0002	0.050	0.42%
Resettable  Fuse Circuit Breaker	(*1)	30	0.004	0.0004	0.120	1.00%
S1	Green	30	0.002	0.0002	0.060	0.50%
Ab	Amber	40	0.001	0.0001	0.040	0.33%
Ax	Amber	40	0.001	0.0001	0.040	0.33%

Summary

Higher rated fuses seem to have a lower resistance.

Between 12 Volt fuses of the same rating is not much variation in the resistance.

The 30 A Resettable Fuse Circuit Breaker seems to have a higher resistance (and higher voltage drop) than a standard 30A 12V fuse.

Also, compared to the 250 Volt fuses in my previous post these 12V car fuses have a much lower resistance !!!

Measuring Resistance of Fuses with a Milliohm Meter and Kelvin Clips -2- (250V Fuses measurement results )

Ensuring the integrity and reliability of 250V fuses is crucial for maintaining the safety and functionality of high-voltage electrical systems. In this post, I'll share my experience measuring the resistance of 250V fuses using an affordable milliohm meter equipped with Kelvin clips, highlighting the key considerations and benefits of this method.

Why Measure Fuse Resistance?

Regularly measuring the resistance of 250V fuses is essential for several reasons:

1. Ensuring Reliability:

Over time, fuses can develop higher resistance due to aging or exposure to harsh conditions.

2. Troubleshooting:

Identifying a fuse with abnormal resistance can help diagnose and prevent circuit issues.

3. Preventive Maintenance: 

Regular measurements allow for the replacement of fuses before they fail, avoiding potential downtime or damage.

Tools Needed

For this task, I used:

- Milliohm Meter:

 Capable of measuring low resistance values accurately.

- Kelvin Clips: 

Four-wire probes that eliminate the influence of lead and contact resistance, providing precise measurements.

The Measurement Process

Here's a quick overview of the process:

1. Calibration:

Ensure the milliohm meter is calibrated using the shorting clip and zeroing function.

2. Connecting Kelvin Clips: 

Attach the clips to the fuse, ensuring a solid, clean connection at opposite ends.

3. Taking the Measurement: 

Power on the meter and read the displayed resistance value.

Voltage Drop Across the Fuse

For a milliohm meter with a measurement current of 100 mA, the voltage drop across the fuse can be calculated using Ohm's Law (V = I × R).

Example Calculation:

- For a measured resistance of 0.005 ohms: 

  - Voltage Drop: V = 100 mA × 0.005 ohms = 0.5 mV

- For a measured resistance of 0.002 ohms: 

  - Voltage Drop: V = 100 mA × 0.002 ohms = 0.2 mV

Change in Resistance Due to Heating

When a fuse is subjected to higher currents, it can heat up, causing its resistance to change:

- Initial Resistance:

The resistance at room temperature is relatively low.

- Heating Effect:

Higher current flow increases temperature, raising the resistance.

- Increased Resistance:

This change can be significant, especially for currents near the fuse’s rated limit.

Measured resistance

I having a long time a box with slow 250V glass fuses with values 50 mA, 160 mA, 200 mA, 315 mA, 500 mA, 800 mA, 1 A, 2 A, 2.5 A. It would be nice to use these fuses as a test-set. 

My box with fuses (open)

I first did think it was needed to measure each fuse several times. However during my first (not documented) test i discovered that remeasuring a fuse id almost gave no variation in the result. (max 1 or 2 in the last digit).  The variation between different fuses of the same rating was much bigger. Therefore i decided to measure all the fuses once and put the results in a table (1).

However there were some limitations: 

- According to the manual, the resistance is measured with a testing current of about 100 mA. ( i did not check this yet.) Therefore i decided to skip to 50 mA fuses as they would be blown an not measured.

- The fuses are relative old. I expect at least 25 years. The nice thing is that it is a set of in total more than 140 fuses of different values and the aging effect of the fuses is included.

- The box with fuses had at (least) two sources. A box with fuses that i did buy many years ago and a similar box with fuses that i received some year ago from someone else. I did merge the content of these boxes a year ago to save some space.

- I noticed some fuses had a resistance far above 1 ohm. (And i expect some of these fuses where bad. I measured with a multi-meter around 200 Ohm and some above 10 Mega Ohm and even some fuses that made no connection at all. I removed these fuses from the box with fuses, kept them apart and did not include the results. I expect the fuses that made no connection at all are blown fuses and i did throw them away.  

- All my 2.5 A fuses had corrosion and the measured resistances where above 1 Ohm. I don't know if this is normal or this was due to aging and/or the corrosion. The strange thing is that all the 2.5 A fuses that had visible corrosion and almost none of the other fuses.  I don't know the source of the corrosion. Perhaps the fuses are of a different material or there was humidity that mainly reached the 2.5 A fuses and not the other fuses. Therefore i excluded all of the 2.5 A fuses.

Results

Below a table with the measured resistance , the calculated voltage drop at 100mA and the voltage drop at the rated current.

Table 1: Measured resistances with calculated voltage drops

Result /  measurement Number	mA	Measured  resistance	Calculated Voltage drop at 100mA	Calculated Voltage drop at rated current
1	500	0.447	0.04470	2.235
2	500	0.477	0.04770	2.385
3	500	0.446	0.04460	2.230
4	500	0.434	0.04340	2.170
5	500	0.520	0.05200	2.600
6	500	0.461	0.04610	2.305
7	500	0.510	0.05100	2.550
8	500	0.536	0.05360	2.680
9	500	0.462	0.04620	2.310
10	500	0.432	0.04320	2.160
11	500	0.502	0.05020	2.510
12	500	0.482	0.04820	2.410
13	500	0.452	0.04520	2.260
14	500	0.465	0.04650	2.325
15	500	0.424	0.04240	2.120
16	500	0.456	0.04560	2.280
17	500	0.469	0.04690	2.345
18	500	0.461	0.04610	2.305
19	160	0.579	0.05790	0.926
20	160	0.570	0.05700	0.912
21	160	0.537	0.05370	0.859
22	160	0.640	0.06400	1.024
23	160	0.409	0.04090	0.654
24	160	0.658	0.06580	1.053
25	160	0.664	0.06640	1.062
26	160	0.531	0.05310	0.850
27	160	0.613	0.06130	0.981
28	160	0.568	0.05680	0.909
29	160	0.677	0.06770	1.083
30	160	0.581	0.05810	0.930
31	160	0.604	0.06040	0.966
32	160	0.619	0.06190	0.990
33	160	0.494	0.04940	0.790
34	160	0.615	0.06150	0.984
35	160	0.689	0.06890	1.102
36	160	0.557	0.05570	0.891
37	160	0.409	0.04090	0.654
38	160	2.900	0.29000	4.640
39	1000	0.088	0.00880	0.880
40	1000	0.089	0.00890	0.890
41	1000	0.092	0.00920	0.920
42	1000	0.087	0.00870	0.870
43	1000	0.089	0.00890	0.890
44	1000	0.089	0.00890	0.890
45	1000	0.087	0.00870	0.870
46	1000	0.089	0.00890	0.890
47	1000	0.087	0.00870	0.870
48	1000	0.094	0.00940	0.940
49	1000	0.091	0.00910	0.910
50	1000	0.096	0.00960	0.960
51	1000	0.089	0.00890	0.890
52	1000	0.087	0.00870	0.870
53	1000	0.089	0.00890	0.890
54	1000	0.092	0.00920	0.920
55	1000	0.091	0.00910	0.910
56	1000	0.090	0.00900	0.900
57	1000	0.090	0.00900	0.900
58	315	0.700	0.07000	2.205
59	315	0.562	0.05620	1.770
60	315	0.761	0.07610	2.397
61	315	0.706	0.07060	2.224
62	315	0.852	0.08520	2.684
63	315	0.805	0.08050	2.536
64	315	0.607	0.06070	1.912
65	315	0.723	0.07230	2.277
66	315	0.681	0.06810	2.145
67	315	0.612	0.06120	1.928
68	315	0.646	0.06460	2.035
69	315	0.884	0.08840	2.785
70	315	0.760	0.07600	2.394
71	315	0.719	0.07190	2.265
72	315	0.871	0.08710	2.744
73	315	0.766	0.07660	2.413
74	315	0.681	0.06810	2.145
75	315	0.620	0.06200	1.953
76	315	0.759	0.07590	2.391
77	315	0.602	0.06020	1.896
78	2000	0.039	0.00390	0.780
79	2000	0.039	0.00390	0.780
80	2000	0.039	0.00390	0.780
81	2000	0.042	0.00420	0.840
82	2000	0.038	0.00380	0.760
83	2000	0.037	0.00370	0.740
84	2000	0.035	0.00350	0.700
85	2000	0.703	0.07030	14.060
86	200	0.331	0.03310	0.662
87	200	0.485	0.04850	0.970
88	200	0.545	0.05450	1.090
89	200	0.405	0.04050	0.810
90	200	0.486	0.04860	0.972
91	200	0.584	0.05840	1.168
92	200	0.490	0.04900	0.980
93	200	0.573	0.05730	1.146
94	200	0.472	0.04720	0.944
95	200	0.442	0.04420	0.884
96	200	0.446	0.04460	0.892
97	200	0.508	0.05080	1.016
98	200	0.515	0.05150	1.030
99	200	0.429	0.04290	0.858
100	200	0.489	0.04890	0.978
101	200	0.395	0.03950	0.790
102	200	0.491	0.04910	0.982
103	250	0.268	0.02680	0.670
104	250	0.517	0.05170	1.293
105	250	0.382	0.03820	0.955
106	250	0.388	0.03880	0.970
107	250	0.385	0.03850	0.963
108	250	0.340	0.03400	0.850
109	250	0.348	0.03480	0.870
110	250	0.366	0.03660	0.915
111	250	0.249	0.02490	0.623
112	250	0.322	0.03220	0.805
113	250	0.338	0.03380	0.845
114	250	0.405	0.04050	1.013
115	250	0.263	0.02630	0.658
116	250	0.361	0.03610	0.903
117	250	0.350	0.03500	0.875
118	250	0.247	0.02470	0.618
119	250	0.349	0.03490	0.873
120	250	0.322	0.03220	0.805
121	250	0.342	0.03420	0.855
122	250	0.371	0.03710	0.928
123	250	0.292	0.02920	0.730
124	800	0.151	0.01510	1.208
125	800	0.136	0.01360	1.088
126	800	0.139	0.01390	1.112
127	800	0.127	0.01270	1.016
128	800	0.133	0.01330	1.064
129	800	0.131	0.01310	1.048
130	800	0.141	0.01410	1.128
131	800	0.128	0.01280	1.024
132	800	0.128	0.01280	1.024
133	800	0.133	0.01330	1.064
134	800	0.136	0.01360	1.088
135	800	0.143	0.01430	1.144
136	800	0.127	0.01270	1.016
137	800	0.128	0.01280	1.024
138	800	0.135	0.01350	1.080
139	800	0.136	0.01360	1.088
140	800	0.132	0.01320	1.056
141	800	0.147	0.01470	1.176
142	800	0.132	0.01320	1.056

Some of the fuses gave results that made me doubt if the fuse had indeed the current rating i expected. However i did check the rating it on the fuse! 

Table 2: Summary of measured resistances  (Some outliers are removed.)

Fuse rating (mA)	Average resistance	Min resistance	Max resistance
160	0.5797	0.409	0.689
200	0.4756	0.331	0.584
250	0.3431	0.247	0.517
315	0.7159	0.562	0.884
500	0.4687	0.424	0.536
800	0.1349	0.127	0.151
1000	0.0898	0.087	0.096
2000	0.0384	0.035	0.042

 

Fuses with a higher rating seem to have a lower resistance, however even in this box with fuses not always!  I decided to already publish the measured results with a quick summary. In an upcoming blog-post i will do a more in depth evaluation of the results.

My box with fuses (closed)

Conclusion

Measuring the resistance of 250V fuses with a milliohm meter and Kelvin clips is a straightforward yet powerful method to ensure the health of your high-voltage circuit protection devices. Regular checks can help you catch potential issues early, maintaining the integrity and safety of your electrical systems. It was also a good exercise to measure these fuses to check the health and variation between these fuses. This affordable and accurate setup is a valuable addition to any toolkit, providing peace of mind and reliable performance.

Stay tuned for more insights and results from my ongoing experiments and measurements and a more in-depth evaluation of these measured results. Happy measuring!

Measuring Resistance of Fuses with a Milliohm Meter and Kelvin Clips -1- ( Car fuses )

In the world of electronics, ensuring the integrity of fuses is crucial for the safety and reliability of circuits. Fuses act as protective devices, preventing excessive current from damaging components. Over time, however, fuses can degrade, leading to increased resistance, which may compromise their effectiveness. Today, I'll share my experience measuring the resistance of some 12 Volt car fuses using an affordable milli-ohm meter equipped with Kelvin clips. This method provides accurate results, essential for maintaining optimal circuit performance.

Why Measure Fuse Resistance?

Measuring the resistance of fuses serves several purposes:

1. Ensuring Reliability: 

Over time, fuses can develop higher resistance due to aging or exposure to harsh conditions. Regular checks ensure they are still effective.

2. Troubleshooting: 

Identifying a fuse with abnormal resistance can help diagnose and prevent circuit issues.

3. Preventive Maintenance:

Regular measurements allow for the replacement of fuses before they fail, avoiding potential downtime or damage.

Equipment Needed

For this task, I used the following equipment:

- Milliohm Meter: 

A device capable of measuring low resistance values accurately. I used a YMC01 2R handheld Milliohm Meter. For details see my previous blogpost. According to the manual this meter uses a testing current of about 100 mA (i did not check this),

- Kelvin Clips:

 Four-wire probes that eliminate the influence of lead and contact resistance, providing precise measurements. These where included with my meter.

- Fuses:

 For the first test i used some some new 12 Volt Car fuses.

Also i tested a fuse in a fuse holder.

Below a table of the color codes of the car fuses.

The Measurement Process

Here’s a step-by-step guide to measuring fuse resistance with a milliohm meter and Kelvin clips:

1. Calibration

Before starting, it’s essential to calibrate the milliohm meter. Follow these steps:

- Turn on the meter and allow it to stabilize.

- Use the provided shorting clip to connect the Kelvin clips together.

- Zero the meter according to the manufacturer’s instructions. This step ensures that the meter reads zero when there’s no resistance. My cheap meter does not have a zeroing function. H

2. Connecting Kelvin Clips

Attach the Kelvin clips to the fuse. Ensure a solid, clean connection:

- Place the clips at opposite ends of the fuse to measure the resistance accurately.

- Make sure there is no dirt or oxidation on the fuse terminals that could affect the reading.

3. Taking the Measurement

With the Kelvin clips properly connected, take the reading:

- Power on the meter.

- Read the displayed resistance value. The milliohm meter should provide a precise measurement free from lead resistance thanks to the Kelvin clips.

Voltage Drop Across the Fuse

For your milliohm meter with a 0-1 ohm range and a measurement current of 100 mA, you can calculate the voltage drop across the fuse using Ohm's Law (U = I × R).

Example Calculation:

1. Voltage drop at 100 mA : 

   - 100 mA = 0.1 Ampere

   - Measured Resistance: 0.004 ohms

   - Voltage Drop: U = 0.1 A × 0.004 ohms = 0.0004 volts (0.4 mV)

2. Voltage drop at current rate:

   - Fuse rating (e.g. 15 Ampere )

   - Measured Resistance: 0.004 ohms

   - Voltage Drop: U = 15 A × 0.004 ohms = 0.060 volts (30 mV)

2. Relative Voltage drop at current rate:

A voltage drop of 0.060 volts is at 12 Volt the relative voltage drop of 100% * 0.060/12 = 0.50 % 

Change in Resistance Due to Heating

When a fuse is subjected to higher currents, it can get hot, causing its resistance to change. This phenomenon is due to the temperature coefficient of resistance, which describes how the resistance of a material changes with temperature. For most metals, resistance increases as temperature increases.

Key Points:

1. Initial Resistance:

 The resistance of a fuse at room temperature is relatively low.

2. Heating Effect: 

As current flows through the fuse, it heats up. The amount of heat generated is proportional to the square of the current (P = I²R).

3. Increased Resistance: 

As the temperature of the fuse rises, so does its resistance. This change can be significant, especially for currents near the fuse’s rated limit.

Example:

If a fuse rated for 1A is subjected to a current close to its limit, it will heat up. The resistance can increase noticeably, potentially doubling or tripling depending on the fuse material and the current applied.

My Measurement Results

For this first test a set of 12 Volt Car fuses (see pictures above) and a 10A fuse with a fuse holder was used.

Table with Results:

Fuse	Rated Current	Measured Resistance	Calculated Voltage Drop (100 mA)	Calculated Voltage Drop at rated current	Calculated Voltage drop at rated current in % relative to 12 Volt
10A (without fuse holder)	10   A	0.008	0.0008	0.08	0.67 %
10A fuse in fuse holder	10   A	0.007	0.0007	0.07	0.58 %
Brown	7.5 A	0.009	0.0009	0.0675	0.56 %
Red	10   A	0.006	0.0006	0.06	0.50 %
Blue	15   A	0.004	0.0004	0.06	0.50 %
Yellow	20   A	0.003	0.0003	0.06	0.50 %
Clear	25   A	0.002	0.0002	0.05	0.42 %
Green	30   A	0.002	0.0002	0.06	0.50 %

Interpreting the Results

- Expected Values:

 Typically, a good fuse should have a very low resistance, often just a few milliohms.

- Anomalies: 

If a fuse shows significantly higher resistance than expected, it might be compromised and should be replaced.

Summary

These resistances are measured with the Milliohm meter. I expect all with around the same current of 100 mA. A higher current will heat up the fuse wire and change the resistance and to get real good conclusions other measurements will be needed. 

The measured resistances of these car fuses where very low (below 0.01 milliohm).

I only had two red 10A fuses (and for the other fuses only one) I measured a resistance of 0.0008 and 0.0006 for these fuses (and 0.0007 ohm for the first red fuse using the fuse holder),

The fuse holder did not add a significant resistance.

The lower rated fuses seem to have a slight higher resistance.

Measuring fuse resistance with a milliohm meter and Kelvin clips is a straightforward yet powerful method to ensure the health of your circuit protection devices. Regular checks can help you catch potential issues early, ensuring your electronics remain safe and functional. By investing in this affordable yet accurate setup, you can maintain the integrity of your circuits and prevent unexpected failures.

Stay tuned for more insights and results from my ongoing experiments and measurements. Happy measuring!