Do I need a diode using a bench power supply for charging battery ? - Page 1
Forum section: electronics / beginners

author: hary
author_rank: Contributor
timestamp: July 02, 2020, 12:39:33 pm
content: HiHere is my quetsion :Do I need a diode using a bench power supply for charging battery ? Is it risky to charge battery with bench power supply without adding a diode in the circuit to avoid current flowing back from battery to the supply in some situation ?

author: Ian.M
author_rank: Super Contributor
timestamp: July 02, 2020, 01:33:58 pm
content: Maybe!Unless you are 100% certain your bench PSU is by design protected against damage from applying a voltage source to its output when its switched off or otherwise has its input power disconnected, and wont draw too much current from the battery if switched off or otherwise powered down, you need a diode. However adding a non-ideal diode brings its own set of problems if you need to get close to 100% charge into the battery.

author: ArthurDent
author_rank: Super Contributor
timestamp: July 02, 2020, 04:39:44 pm
content: At one job I had at a weather station on top of a mountain they had a data logger that was powered by a 12 volt car battery that was always on charge from a Astron power supply. After they had 2 of the power supplies burn up in a short period of time I was asked to find out why. The data logger was quite a distance from the battery and power supply and thunder storms were common on the summit and mains power could be somewhat iffy so they needed the battery for backup.What was happening was that transients were induced in the long wires connecting the battery to the data logger and the power supply connected to the battery had a protective circuit (an SCR 'crowbar') to protect any device connected to the supply from overvoltage. These spikes caused the SCR to fire shorting the supply output but with the battery connected directly to the output, something had to give, and that was the runs on the circuit board which were vaporized. The solution was to put a diode in series with the new supply output to prevent any voltage being fed back into the supply. Now you could use a mosfet connected as an extremely low forward drop diode and not have to worry so much about full charge.The Riden RD6006 has a battery charge function which can be helpful

author: hary
author_rank: Contributor
timestamp: July 02, 2020, 05:18:26 pm
content: Thanks for the response.But How can I know about a specific power supply model.For my personal use, I use some little Riden DP5005 or so, and they have this very useful feature for me as I often have to deal with battery.But at my work, I don't think they would order from AliExpress.And they'll like something that look more "professionnal".I was maybe thinking something like thishttps://www.welectron.com/Siglent-SPD1305X-Benchtop-Power-Supplyor thishttps://www.reichelt.com/fr/fr/laboratory-power-supply-0-60-v-0-6-a-2x-usb-peaktech-6227-p270048.html?PROVID=2788&gclid=CjwKCAjwi_b3BRAGEiwAemPNU3jmylTXhFwN-azHtSvFDLBJhhei0Lr3m4e5iULOHdrZjmwRreJ-oRoCS0UQAvD_BwE&&r=1I absolutely need the battery charging protection feature.Otherwise, I'm pretty sure, it won't last, it will be burn after a month or so by one of my colleague or even me by mistake.But that feature is't cleary advertised !

author: wizard69
author_rank: Super Contributor
timestamp: July 02, 2020, 06:37:48 pm
content: Well to n extent it depends upon the supply. However since most power supplies are not designed to be battery chargers there is a (very) high risk of blowing out the supply! This actually happened in the tech classes I took many moons ago, somebody wanted to charge a battery and turned off the power supply before disconnection. zap. So yeah it does happen and can lead to significant damage.Quote from: hary on July 02, 2020, 12:39:33 pm

author: hary
author_rank: Contributor
timestamp: July 02, 2020, 06:57:25 pm
content: So I'll insist with my company to get a Riden RD6006, even if it's sold as a kit !

author: David Hess
author_rank: Super Contributor
timestamp: July 03, 2020, 08:35:27 pm
content: Quote from: hary on July 02, 2020, 05:18:26 pmCheck the schematic included in the documentation. You selected your power supply because it came will full documentation including a schematic, right? RIGHT?

author: wizard69
author_rank: Super Contributor
timestamp: July 03, 2020, 08:45:07 pm
content: Not at all. If this is for a commercial operation force them to buy a batter charger designed for the job at hand. I can imagine any company being in a position where they can't buy a proper battery charger. Beyond that there are liability issues to consider. This isn't a situation where a hobbyist is working at his bench.Quote from: hary on July 02, 2020, 06:57:25 pm

author: janoc
author_rank: Super Contributor
timestamp: July 03, 2020, 09:18:20 pm
content: Quote from: hary on July 02, 2020, 06:57:25 pmWhy not get an actual, proper charger for your battery? Which actually includes also various safety features against overcharging the battery, charging a damaged battery, overheating and starting a fire?Buying a bench power supply to charge batteries is a very dumb (and potentially really expensive!) idea.

author: ledtester
author_rank: Super Contributor
timestamp: July 04, 2020, 12:35:04 am
content: Quote from: Ian.M on July 02, 2020, 01:33:58 pmWould a power supply with remote sensing solve this problem - i.e. when using it as a charger, add the diode (say at the positive terminal) and sense at the cathode of the diode?

author: ArthurDent
author_rank: Super Contributor
timestamp: July 04, 2020, 02:48:30 am
content: Quote from: ledtester on July 04, 2020, 12:35:04 amGenerally there is a limit to the voltage difference between the output terminal and the sense terminal for that output terminal, generally less than 1 volt. Exceeding that value could damage the sense circuitry in the supply and this limit could be exceeded if the battery was feeding voltage into the supply through the sense leads while the output terminals were isolated by a diode. It would be safer to compensate for the fraction of a volt diode drop from a mosfet connected as a near ideal diode.https://www.edn.com/power-supply-remote-sense-mistakes-remedies/

author: JustMeHere
author_rank: Frequent Contributor
timestamp: July 04, 2020, 03:11:33 am
content: It's not a bad idea. If you see a spark when you hook it up, you probably should.I've done this with a TP3005. I had a spark w/o the diode.

author: Gregg
author_rank: Super Contributor
timestamp: July 04, 2020, 04:02:02 pm
content: From a comparison chart copied from Banggood's website it appears that the Riden DPS5005 is rated to charge batteries.I have a Riden DPS3012 set up to float 4 large flooded lead acid spare cells on a friend's off grid setup; this little power supply has been in use for three years constantly without issue. The input is 24V nominal and the output is 9.06V; I have 10A automotive style fuses on both the input and output.

author: hary
author_rank: Contributor
timestamp: July 04, 2020, 05:24:32 pm
content: Actually, the main purpose for that power supply isn't for charging battery.It's meant to test an embedded system that works on battery.When it's plugged to the main, the charger will charge the battery. When unplugged, the system will run on its own battery.But as I need to test the charging "algorithm" and the battery management depending on voltage level (lead acid battery), I need some kind of way of simulating the battery voltage changing and see if the system switch off as expected when the voltage is too low, or allow the system to start if the battery is ok.So if I power the system from the bench power supply, when plugged in the main, in case of simulating a dead battery, the main supply will inject power back to the bench power supply.That's the reason I wanted a bench power supply that can charge battery without any problem.

author: Trader
author_rank: Frequent Contributor
timestamp: February 04, 2023, 03:45:35 am
content: I'm using a PSU to charge a 6V VRLA battery and, since I don't know if my PSU has backfeeding protection, I'm using a 1N5822 (Schottky diode with low drop-voltage).But I found that using an Ideal Diode (2 MOSFETs with a control circuit around them) could be better.Any opinions?

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 12:06:56 pm
content: as a side note, FWIW, I have yet to see a PSU (at least of the CC/CV capable ones) that would be damaged by backfeeding from the battery. I have, however, seen ones drawing significant current, for example, 50 mA. The lowest I have seen was 2 mA, and a typical DC/DC buck module from Aliexpress will draw about 14..20 mA.(all current values were measured with ~12-13V batteries)Quote from: Trader on February 04, 2023, 03:45:35 amThis works and gets rid of the guesswork concerning the possible PSU damage or the parasitic battery drain, but, however low the diode voltage drop is, it is still non-zero. It wouldn't be much of a problem if it was only non-zero (just crank up the CV setting, and you're fine, right?), but it's also not constant and depends on current, thus making it impossible to set a precise final voltage, unless the PSU has a dedicated set of wires to sense it right at the battery terminals.Quote from: Trader on February 04, 2023, 03:45:35 amIt will definitely be better. Please share the circuit you have in mind (or maybe even tested?). I would be interested to try one myself.

author: blackdog
author_rank: Frequent Contributor
timestamp: February 04, 2023, 02:01:39 pm
content: Hi,Yes always include and diode in series for your safetyy!Modern batteries get more and more energy and many quickly forget this and how dangerous it can be.People are walking away from the installation that charges the batteries etc.Of course I am aware, that some power supplies can stand it if you reverse the + and -, but there are not many of them, especially in the hobby circuit.Even if you would not reverse the polarity of the battery to be charged, it can still go well wrong.If the power supply is turned off power transistor can get a reverse voltage, not every power supply has a diode built in for this.Another example, the battery is 24V and the power supply is set to 5V, BANG! if you don't use a diode.And I know of other situations that can cause battery charging to go wrong....Charge batteries with chargers made for that!Still use a Power Supply, then include a suitable diode!Charge Li-Ion? use a suitable charger!I know many who disregard this advice, on a Dutch forum the same discussion, and then find it strange that their Power Supply burns out....Comments like this then come along, if I include a diode I can no longer charge exactly to 4.25V,that's what I mean, take a suitable charger and not your Power Supply.But, do what you yourself find suitable, I choose safety, this to keep my measuring equipment in one piece and then my LAB does not burn down.And now let's wait for the first one to come forward with the comment that he has been doing it for years without a diodeand has never had any problems, good for you!Kind regards,Bram

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 02:16:02 pm
content: Using equipment not exactly designed for the job is not inherently unsafe. It only puts additional responsibilities on the user to keep the process safe, most important of which is a full understanding of exactly what processes take place and what constraints have to be met to stay in the safe operating area. When charging a lithium battery, for example, there are not many of them, pretty much limited at:- do not exceed max allowed voltage per cell (and min voltage for discharge);- do not exceed max allowed current, both charge and discharge;- make sure that the temperature stays within the allowed range and that the battery charged at a low ambient temperature is not then stored at a much higher temperature being still fully charged.As long as these conditions are met, the battery does not care if it is being charged with a designated charger. It's up to the user to make sure that they are met, either by utilizing his (her?) own knowledge and experience, or by relying on those of the charger manufacturer's.

author: blackdog
author_rank: Frequent Contributor
timestamp: February 04, 2023, 03:14:33 pm
content: Hi shapirus,The issue is not whether the battery is aware of how it is being charged.The issue is that the person connecting a battery to a Power Supply is aware of what dangers it can pose if he or she does not think about what they are doing.Much of humanity is pretty lazy,I'll do it this way, oh well for that one time it can be done the quick way, etc.And YES!- do not exceed max allowed voltage per cell (and min voltage for discharge);- do not exceed max allowed current, both charge and discharge;- make sure that the temperature stays within the allowed range and that the battery charged at a low ambient temperature is not then stored at a much higher temperature being still fully charged.Just look at the many youtube videos that will make your neck hairs stand up.Most people often become aware of the consequences when confronted with them.This question is in the beginners section and I think it is good to point out to beginners, what the safe practice is for charging batteries.Kind regards,Bram

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2023, 03:20:25 pm
content: In my opinion, definitely no diode needed.But there are some total and utter crap "bench power supplies" that die on a battery load, or pre-biased capacitive load. But even if you use the diode, these con devices will die from any other random cause anyway, so the sooner they self-destruct, the better, so you can claim for money back and learn the lesson what to buy.Quote from: blackdog on February 04, 2023, 02:01:39 pmDangerous "advice." DIODE IS NOT A SAFETY DEVICE. A diode easily fails as a short circuit. If in doubt about the quality of bench supply, use afuse(in addition to / instead of a diode), which is an actual safety device. With a battery that can source a lot of current, a fuse with high interrupt rating is recommended; a sand-filled type for example (always read the datasheet).Of course, one can not leave a bench power supply charge a li-ion cell without monitoring.Charging batteries with lab supplies is their normal intended use, but you need to know exactly what you are doing, and monitor the battery pack, acting as a battery management system yourself.

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 03:22:02 pm
content: Quote from: blackdog on February 04, 2023, 03:14:33 pmYes, this is precisely what I meant referring to the knowledge of the processes that are taking place. Another issue here is that the user must not only think that he/she has the knowledge, but actually have this knowledge.OTOH, it's not rocket science. Know what to avoid, know what to do, know what to measure and how to measure properly, know the Ohm's law, ideally have a fire-proof metal case handy (if you're playing with Li-ion/LiPo stuff), make sure you know what you're doing and you'll be good to go. How do you get experience if you don't do anything?

author: blackdog
author_rank: Frequent Contributor
timestamp: February 04, 2023, 03:52:39 pm
content: SiwastajaYou are the first!In my opinion, definitely no diode needed, That's nice advice, did you really think before typing it here?Dangerous "advice." DIODE IS NOT A SAFETY DEVICE.,Another comment that hasn't really been thought about I think,A 1N4148 is not a part you are going to use e.g. for a charging current of say 4-Ampere, for that you use a diode that can handle well over the charging current needed and also the difference voltage between the battery and the power Supply.Include an extra fuse for safety, my blessing you have, basically a good idea.Who told you this:Charging batteries with lab supplies is their normal intended useJust a small peace from een KeySight power supply, with only one possibility of what could go wrong ...Reverse Current LoadingActive loads connected to the power supply may actuallydeliver a reverse current to the power supply during a portionof its operating cycle. An external source can not be allowedto pump current into the supply without loss of regulation andpossible damage to the output capacitor. To avoid theseeffects, it is necessary to preload the supply with a dummyload resistor so that the power supply delivers current throughthe entire operating cycle of the load devices.And a little more general info on this topic from KeySight:https://edadocs.software.keysight.com/kkbopen/what-can-cause-a-power-supply-output-voltage-to-exceed-its-setting-583423316.htmlKind regards,Bram

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2023, 04:48:51 pm
content: "possible damage to the output capacitor" just means they have a capacitor at output, which is obvious, and if you apply a battery voltage which exceeds the voltage rating of that capacitor, it might get damaged. Quite obviously, the battery voltage must be within the range of the supply.Also one can claim that the inrush current of suddenly connecting a battery could damage the output capacitor, but the current is exactly the same when just shorting the output of the supply.The difference is here:Bullcrap power supplies blow up when you connect a battery,andthe manual probably says nothing about it (if there is a manual at all).Keysight supply will definitely not blow up, but theyneverthelesscover their bases in their manual. Instead of having to specify stuff like "external battery voltage must be between xx - yy V", they just say don't do it.And loss of regulation? No shit Sherlock, that's obviously what happens, unless it's a two-quadrant supply. Loss of regulation does not mean damage.Some lab supplies have a configurable OVP with possibly some hard limit beyond the maximum output voltage. Know your equipment.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2023, 04:56:24 pm
content: Quote from: blackdog on February 04, 2023, 03:52:39 pmI told you. Some of us do this professionally instead of passive aggressive shitposting. Uses of lab supplies are various. They are pretty useless if you have to construct special circuits for every basic need. Prebiased loads are completely normal and not limited to batteries. Just any normal DUT can have tens of thousands of uF of input capacitance.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2023, 04:58:22 pm
content: Quote from: blackdog on February 04, 2023, 03:52:39 pmIt would be nice if you read your own links...It is possible for an external source of power (such as a battery, charged capacitor, inductor with changing current, or another power supply) to cause the voltage to go above the setting. The OVP will respond to this condition as outlined above. If the external power source can provide more current than the rating of the power supply and an SCR circuit is used in the power supply, it is prudent to put a fuse in series with the external source of power to prevent damage to the power supply SCR and/or output circuit from excessive current.TLDR: nothing about diode. Use a FUSE.Another question for you, what do you think the current will be when the output capacitor with ESR=X and voltage=Y is connected to a battery with ESR=Z and voltage=Å? Hint: the fact that you set the current limit at 4A is meaningless. Question: what do you think happens to your 4A rated diode? Do you know how to interpret SOA curves?

author: Trader
author_rank: Frequent Contributor
timestamp: February 04, 2023, 05:51:42 pm
content: Quote from: shapirus on February 04, 2023, 12:06:56 pmThe Lead-Acid Battery, usually is fully charged when the current stabilizes at 0.01C (my battery is 7Ah, so doesn't decrease more than 70mA).I verified that my 1N5822 from 3mA to 100mA has basically the same drop-voltage 290mV, so I set up the charging voltage to 7.79V, and when full-charged, the voltage will be up to 7.5V (I'm doing a Cycle charge [7.2V to 7.5V], not a Float charge [6.9V]).Quote from: shapirus on February 04, 2023, 12:06:56 pmI didn't develop one yet but look for an "ideal diode" on eBay/Aliexpress, there are a lot of models, and cheap (just 2 MOSFETs, capacitors, very simple).

author: Trader
author_rank: Frequent Contributor
timestamp: February 04, 2023, 06:03:52 pm
content: About using a Battery Charger instead of my PSU: I'm a hobbyist, I like to explore and learn, the PSU is fine if you respect the already cited rules:- do not exceed max allowed voltage per cell (and min voltage for discharge);- do not exceed max allowed current, both charge and discharge;- make sure that the temperature stays within the allowed range and that the battery charged at a low ambient temperature is not then stored at a much higher temperature being still fully charged.In fact, with a PSU I can have much more control of the Voltage and Current, and since I just do this eventually, isn't necessary to buy a 6V/12V/24V charger, and I guess that even those chargers are not so good in following those rules.

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 06:10:50 pm
content: Quote from: Trader on February 04, 2023, 05:51:42 pmmeh, thanks. Moral: whenever you want to DIY something, rest assured, AliExpress is always ready to spoil the fun

author: Trader
author_rank: Frequent Contributor
timestamp: February 04, 2023, 06:29:43 pm
content: Quote from: Siwastaja on February 04, 2023, 04:58:22 pmThis is interesting. I'm using a Diode to avoid the back feeding when turning the PSU off with a battery connected to it, other posts on this thread related to burning PSUs because of the Back-Feed.I'm sure the fuse won't protect the backfeeding, and about the current, I just measure the resistance of my PSU when off and it's 920 ohms (maybe there is a correct way to measure its impedance), but in a 24V battery this is just 26mA, so, the fuse will be useless and the diode can handle it very well, even a surge.This is an interesting topic, I won't buy a charger because most of them are crap, maybe I can develop a circuit to charge batteries with limited voltage and current (like the PSU), and this back-feeding issue must be handled.(https://www.st.com/resource/en/datasheet/1n5822.pdf)

author: blackdog
author_rank: Frequent Contributor
timestamp: February 04, 2023, 07:38:20 pm
content: Hi,I also keep in mind this is a topic in the beginners section of this forum.Safety has many faces, also with Power Supply's.I develop Power Supply's and try to think about what can go wrong if the user has a moment of not thinking before doing.A beginner usually does not have a professional Power Supply from KeySight which I have shown some info from.The average hobbyist does not have a thick Thyristor across the output of his Power Supply and does not have all those safety measures that the fancy Power Supply's from Harrison, HP, KeySight and some others, usually all have.If you are going to charge with e.g. a current of say 4-Ampere then you are not going to take a diode just that can handle 4-Ampere, then you choose something that can handle say 20-Ampere or moreand again think about the reverse voltage of the diode.It is often beneficial to use a dual Schottky diode to keep the voltage drop low across the diode.Also consider cooling of the diode at higher currents.Again, so also keep in mind the reverse voltage of your diode!The series diode is primarily intended to ensure that you do not send energy back into the Power Supply to do damage.If you still want to use your power supply to charge batteries, then including a good fuse in series is an extra layer of safety.ExampleBelow is a not complete description of how to connect and charge a car battery for charging.The point is to give you a direction on how to carry it out, additions I would love to hear.Measure the voltage of the battery you want to charge e.g. a car battery.This measures e.g. 11.3V, you use a thick Schottky diode(heatsink?) and you use a fuse suitable for your application.Turn on your Power Supply and set it to e.g. 12V for this car battery and also set the maximum current you want to charge it with, then connect the plus pole in the Power Supply last.This way is to keep the difference between the battery voltage and the Power Supply Voltage as small as possible so that large surge currents do not flow,if your Power Supply has a large capacitor across its output terminals, this is common with smps power supplies.Slowly increase the voltage of the Power Supply until it charges with the current you want, but also measure the voltage at the battery terminals.Be sure not to exceed the maximum voltage for the battery you want to charge.Make sure you can quickly disconnect the battery or Power Supply if calamities occur.If your battery is charging, don't hang out with the neighbors for dinner.Check the temperature, charge current and the battery voltage regularly.Battery voltage is different from de Power Supply voltage if using a diode and fuse!Kind regards,Bram

author: shapirus
author_rank: Super Contributor
timestamp: February 04, 2023, 08:03:19 pm
content: Quote from: blackdog on February 04, 2023, 07:38:20 pmThis should be generalized for ALL components, not just diodes, as follows:- read the datasheet for the component which you are going to use in your circuit and make sure that you: a) understand what it says; b) keep the component within the recommended operating conditions range, including those boring thermal requirements.

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 05, 2023, 09:43:51 pm
content: Quote from: shapirus on February 04, 2023, 12:06:56 pmYou may easily find such PSUs with a simple test. Take a powerful enough and charged battery (e.g. >=12 Ah) and set the PSU output voltage much lower than 12-13 VDC, e.g. 3-5 VDC (lower voltage like 1-2 VDC may work even better).

author: shapirus
author_rank: Super Contributor
timestamp: February 05, 2023, 10:02:04 pm
content: Quote from: Vovk_Z on February 05, 2023, 09:43:51 pmMaybe. I didn't think of this scenario. What I did test was to keep the battery connected to the PSU's output terminals with the input terminals being unpowered while the PSU's output voltage was set to the battery charge end / float value (e.g., 13.6 V for a 4s LiFePO4 battery).In practice this is what happens when a battery is being charged, or, having reached the CV level, is staying in buffer mode, and the PSU/charger input gets powered off, e.g., in case of mains power outage. Worst case that I have seen so far when this happened was ~50 mA draining from the battery back into the charger.

author: Trader
author_rank: Frequent Contributor
timestamp: February 05, 2023, 10:49:46 pm
content: Quote from: Vovk_Z on February 05, 2023, 09:43:51 pmThis isn't so clear to me, how can I verify if the PSU has back-feeding protection, measuring the current in reverse? But why this reverse current wouldn't damage the PSU?

author: shapirus
author_rank: Super Contributor
timestamp: February 05, 2023, 11:05:02 pm
content: Quote from: Trader on February 05, 2023, 10:49:46 pmWhy would it? It could, potentially (I have never seen this, but it doesn't mean it can't happen), but sometimes this current will, for example, simply light up a LED or something. It's actually an interesting question, I wonder where those 50 mA went in that PSU/charger that I mentioned. It didn't seem that this current did any harm, but still it was dissipated in something beyond lighting up that LED. Could also be in poorly chosen (too low) resistors in the feedback divider, for example. Maybe something else too.

author: nightfire
author_rank: Frequent Contributor
timestamp: February 05, 2023, 11:32:07 pm
content: Quote from: blackdog on February 04, 2023, 07:38:20 pmQuestion: Does "plus pole last" mean that the intended sequence would be:1) minus pole of battery2) minus pole of power supply3) plus pole on battery4) plus pole on power supplyI mean, in car charging or giving starting help the minus should get connected last, if I remember correctly- would love to understand the underlying mechanisms in the PSU!

author: Trader
author_rank: Frequent Contributor
timestamp: February 06, 2023, 04:41:03 am
content: I just bought these cheap Ideal Diodes:https://s.click.aliexpress.com/e/_DCVtEoDOne of the reviewers said:QuoteI guess the Drop Voltage is related to Current, not Voltage, so, seems that ~1A is ~50mV. I'll use ~0.5A, maybe the drop will be ~25mV, what's great for me.

author: shapirus
author_rank: Super Contributor
timestamp: February 06, 2023, 09:58:39 am
content: Quote from: Trader on February 06, 2023, 04:41:03 amBeware, there are two kind of "ideal diodes": one protects agains reverse polarity, the other also blocks reverse current. From what I have found in terms of circuits, the latter is a little tricky to implement with discrete components, and there are ICs which do the job of controlling the switches. Looking at the photos of what you bought, I think that it's the first type. When they arrive, check what they actually do and whether they block reverse current. If they do, let us know, I'll then order some tooand probably try to reverse-engineer them, since they use a minimal number of components which is interesting.