A more idiotproof PSU, what is this feature called so I can shop for it?

[vk6zgo]

My DSE 3800/Manson EP 925 supply is  an old style linear supply.
It is generally, pretty dire, but it does have reverse protection in the form of a diode connected from the PSU positive output terminal back to the positive terminal of the 47000uF filter capacitor situated straight after the rectifier.

If a battery is reverse connected across the PSU output, the diode will conduct, & reverse current will flow through the big electro, protecting the components downstream.
Not the healthiest thing for the electro, but it will probably survive a few short reverse charges like this over its lifetime without harm.
Certainly, it is much more rugged than the downstream components.

The diode is only a 1n5401, so it doesn't really have high enough ratings for the job, but is definitely a lot better than nothing.

[alm]

This is a really good point, and upon further consideration, there's no reason that any test lead should ever be unfused, except I figure that would make them mechanically snag on things. Figure someone could make a banana plug with an integrated fuseholder that would probably solve that, but has anyone ever done so? Doesn't look that way.

How about the series resistance, adding an error when measuring resistance and increasing the burden voltage when measuring current. Or what if the fuse blows without you noticing, then you use it to measure voltage, and your meter reads 0V?

The big brands like Fluke have fused test leads, but they have parallel resistors and other protection devices that make sure they still read voltage when the fuse is blown. They don't look like they're designed for battery charging.

My DSE 3800/Manson EP 925 supply is  an old style linear supply.
It is generally, pretty dire, but it does have reverse protection in the form of a diode connected from the PSU positive output terminal back to the positive terminal of the 47000uF filter capacitor situated straight after the rectifier.

Are there decent linear bench supplies that don't have this anti-parallel diode? The diodes are designed for a current-limited source. So usually when you reverse connect a battery, it will dump dozens of amps in this diode, blow it, and then proceed to blow other parts like transistors. That's the failure mode I have seen.

[vk6zgo]

My DSE 3800/Manson EP 925 supply is  an old style linear supply.
It is generally, pretty dire, but it does have reverse protection in the form of a diode connected from the PSU positive output terminal back to the positive terminal of the 47000uF filter capacitor situated straight after the rectifier.

If a battery is reverse connected across the PSU output, the diode will conduct, & reverse current will flow through the big electro, protecting the components downstream.
Not the healthiest thing for the electro, but it will probably survive a few short reverse charges like this over its lifetime without harm.
Certainly, it is much more rugged than the downstream components.

The diode is only a 1n5401, so it doesn't really have high enough ratings for the job, but is definitely a lot better than nothing.

I checked the schematic again, & the diode was part of a protection scheme for the case where an excessive voltage is applied to the output terminals by a battery when using the correct connections for battery charging----not protection from reverse connection.
Please ignore my previous comment.

[rsjsouza]

@vk6zgo, there is an interesting page that talks about several improvements to the Manson EP925 and it might be useful for you. I did some of these to my BK Precision BK1686 (Manson EP 920).
https://pa0fri.home.xs4all.nl/Diversen/EP925/ep925eng.htm

[Myself]

My DSE 3800/Manson EP 925 supply is  an old style linear supply.
It is generally, pretty dire, but it does have reverse protection in the form of a diode connected from the PSU positive output terminal back to the positive terminal of the 47000uF filter capacitor situated straight after the rectifier.

Are there decent linear bench supplies that don't have this anti-parallel diode? The diodes are designed for a current-limited source. So usually when you reverse connect a battery, it will dump dozens of amps in this diode, blow it, and then proceed to blow other parts like transistors. That's the failure mode I have seen.

I put this diode in some of my designs, but it's always behind a fuse (or PPTC) which will blow if the diode is forced into conduction. That's the diode's purpose, to provide a path to blow the fuse, not to just sink current until it explodes. I can't imagine providing the diode without the corresponding fuse. What are they thinking?

[alm]

A good voltage source should have a very low output impedance, so I imagine that's why they don't add a fuse to the output. They designed for current limited sources, like another bench supply, a voltage regulator with over-current protection, etc. Not for a huge cap or high-capacity low-impedance battery. That the user chose to use the bench supply as battery charger is not the responsibility of the company making bench power supplies that in the manual tell you to not charge batteries without series diodes.

There is actually another failure mode where you would need series diode: if the power to the bench supply shuts off for some reason, the battery would be reverse-biasing the pass transistor, something they often don't like either. And if the power supply has an overvoltage crowbar, triggering this, and thus shorting the battery can also give a huge fireworks. So in short, use a battery charger for charging batteries, and if you must use a bench supplies, use series diodes.

[tautech]

The only point in this thread is the careless mistake the OP made with his PSU. 
Tough lessons they are too but I have a mainboard of an X-E that I can take pics of and maybe partly RE the output stage to help with a repair.

There is some helpful info in the Service manual to help effect a repair in Ch5 HW troubleshooting.
P38 https://siglentna.com/wp-content/uploads/dlm_uploads/2019/08/SPD3000X-Series-Service-Manual.pdf
All fusing is on the Power PCB.

Control/Output PCB
Some values below that may help with a repair if the parts are too charred or vaporized.
Some control board pics attached.....2 components that may not be identifiable:
TO-220 BTA08-600C Thyristor
1N5402 power diode across each output

Further pic in next post due to forum size limits....

[tautech]

Further pic

[vk6zgo]

A good voltage source should have a very low output impedance, so I imagine that's why they don't add a fuse to the output. They designed for current limited sources, like another bench supply, a voltage regulator with over-current protection, etc. Not for a huge cap or high-capacity low-impedance battery. That the user chose to use the bench supply as battery charger is not the responsibility of the company making bench power supplies that in the manual tell you to not charge batteries without series diodes.

There is actually another failure mode where you would need series diode: if the power to the bench supply shuts off for some reason, the battery would be reverse-biasing the pass transistor, something they often don't like either. And if the power supply has an overvoltage crowbar, triggering this, and thus shorting the battery can also give a huge fireworks. So in short, use a battery charger for charging batteries, and if you must use a bench supplies, use series diodes.

That is what the diode in the D3800/EP925, which I mistakenly thought was for reverse connection protection, was actually for.
If what you suggested happens, the diode conducts, feeding the battery volts to the large electro, which charges, bypassing the downstream components.
It still assumes that you discover the problem by the time the capacitor charge reaches the applied battery voltage less 0.7v, & the diode cuts off.

I have successfully used bench supplies to charge batteries, & on several occasions successfully "let the smoke out", but meh, I "took my lumps" & moved on.

[capt bullshot]

Regarding reverse polarity protection:

This is an excerpt from the schematic of a "universal" battery charger that I've build about 20 years ago:



T1 and T2 provide reverse polarity protection on the input side,
T9 for the output side.

This part of the circuit controls T9:


One of the key features of this reverse polarity protection is: The reversed input / output is high impedance during the fault, no nothing gets toast.

http://wunderkis.de/charger/index.html

[jonpaul]

Series power diode or Schokkty  at output before FB loop

Shunt opposed diode across output for rev ol protect.

See 1960s..1980 Hewlett Packard lab PSU schematics.

Jon