Longwei power supply problem Model LW-K3010D - Page 1
Forum section: electronics / repair

author: SherylinRM
author_rank: Contributor
timestamp: June 05, 2021, 02:37:09 am
content: HelloIt was suggested by half wave of DIY Solar Power Forum that you may be of some help to me.I have the Longwei Power supply 30 volt 10 amp device.It refuses to charge above 26.50 volts for some reason.Nothing has changed from the other times I have used it to charge my batteries.Thank you for any help you may be able to give me.EDIT: I realize I should have mentioned it is the LW-K3010D.Thanks again for any help in this matter.

author: bdunham7
author_rank: Super Contributor
timestamp: June 05, 2021, 12:44:33 pm
content: So there are two digital displays (Volts and Amps), two knobs and then two lights next to them--green for Volts and red for Current. If you connect your batteries and turn both knobs all the way up, what is indicated on the displays and lights?

author: SherylinRM
author_rank: Contributor
timestamp: June 05, 2021, 01:15:15 pm
content: 26.50 volts and 0 amps

author: SherylinRM
author_rank: Contributor
timestamp: June 05, 2021, 01:17:02 pm
content: How the heck would I add an additional boost converter module and what is it?It does not need to go above 29.2 volts. So maybe I don't need the booster.

author: bdunham7
author_rank: Super Contributor
timestamp: June 05, 2021, 01:40:55 pm
content: Quote from: SherylinRM on June 05, 2021, 01:15:15 pmOK, and the two lights? I'll assume the green one is on and the red one (current) is off. If that's not right, tell me.It seems as if there isn't any output.How about if you disconnect the battery and just leave nothing connected to the front of the power supply? What are the readings then--again both knobs turned all the way up?

author: bdunham7
author_rank: Super Contributor
timestamp: June 05, 2021, 01:51:13 pm
content: Quote from: Mechatrommer on June 05, 2021, 01:42:48 pmI'm not so sure that would be "less stressful" to the PSU because it would have to put out more current. Anyway, we don't know if the PSU here is putting out any power in the first place.

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 03:23:14 am
content: Quote from: bdunham7 on June 05, 2021, 01:40:55 pmOk so when just turned on and nothing attached the green light comes on and the readings are all at zero with both knobs at zero and also when turned all the way up.But a strange thing. The fan comes on which it never did before until it got hot.

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 03:26:07 am
content: The readings when attached were 26.50 and it stopped when it got there. Even though I originally set it for 29.2 volts and highest amps which is 10.Hopefully this clears things a bit.When it stopped the voltage said 26.50 and the amps said zero and only the green light was on.This was when I had it attached to the batteries.

author: bdunham7
author_rank: Super Contributor
timestamp: June 06, 2021, 03:29:00 am
content: Alright, it just doesn't have any output. The voltage you were seeing was from the battery. It's broken. The fan coming on could indicate some fault or maybe something is getting hot now, but unless there is some resettable circuit breaker on the back or a fuse, I don't see any way to revive it unless you want to dive into the somewhat dangerous and frustrating world of repairing cheap, high-energy switch mode power supplies. If you do take it apart for any reason, please be very careful--there is very high voltage inside, higher than in a wall socket or home electrical panel. That voltage can remain even if the unit is turned off and unplugged.

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 03:38:24 am
content: Quote from: bdunham7 on June 06, 2021, 03:29:00 amI seen someone shoot across the room from touching an old TV set once. He barely lived and was not right afterwards.I also was electrocuted once [long story] and it is not fun.So I think I will pass on opening it up unless it is an easy fix like resistor or diode or such.Thanks for your help.Any ideas for a good replacement? Links? I need it to go to 29.2 volts and shut off when it reaches there.Thanks again.

author: bdunham7
author_rank: Super Contributor
timestamp: June 06, 2021, 04:18:09 am
content: All of those lightweight SMPS 30V/10A supplies are cheap junk and not ideal for battery charging. Some are designed poorly enough that they will instantly fry when connected to a battery because they allow high sinking currents--they just aren't designed for battery use. The ones that don't blow up right away are often marginally built and don't last long when putting out full power for extended times. Out of all the cheap junk, this Kaiweets model might be good enough--and there's a return policy and warranty if it isn't:https://www.amazon.com/KAIWEETS-Adjustable-Switching-Regulated-Interface/dp/B085S34NNW/ref=sr_1_5?dchild=1&keywords=kaiweets+power+supply&qid=1622952185&sr=8-5Do you need 10 amps charge current? There are some like these that have lower maximum currents (4 amps in this case) and weigh a ton, but will last a million years or so.https://www.ebay.com/itm/184150581811?hash=item2ae03ae233:g:XTYAAOSwngJeLzEy

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 04:36:25 am
content: Quote from: bdunham7 on June 06, 2021, 04:18:09 amAs for needing 10 amps. My cells are 280 amps. So yeah, ten amps as a minimum would be nice LOL.At 4 amps it would take at least 70 hours to charge if I let them go to zero LOL.Thanks for the link.So you think that this one is a good one then?https://www.amazon.com/KAIWEETS-Adjustable-Switching-Regulated-Interface/dp/B085S34NNW/ref=sr_1_5?dchild=1&keywords=kaiweets+power+supply&qid=1622952185&sr=8-5

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 04:43:21 am
content: Ok then so what IS a good decent one then?Links? Price?Thank you everyone.

author: bdunham7
author_rank: Super Contributor
timestamp: June 06, 2021, 04:45:36 am
content: Quote from: SherylinRM on June 06, 2021, 04:36:25 amI wouldn't go that far...we're still talking about thrifted designs here.I saw a 20A model, but I don't know anything else about it. The connections on the back look good.https://www.amazon.com/Triple-Output-Continuously-Adjustable-Hand-held-Equipment/dp/B089W5CP5L/ref=sr_1_3?dchild=1&keywords=mp3020d&qid=1622954569&sr=8-3

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 05:10:23 am
content: I live on disability so I can't keep buying a new one every couple of months. I would rather pay once and then be able to use it for a few years.I need it for my mobility scooter batteries.I bought lifepo cells for my mobility scooter. I love the power and the range I have now. But having a heck of a time trying to get them charged though.EDIT: Anyone have a reliable power supply they have used for a couple of years or so for charging batteries?

author: bdunham7
author_rank: Super Contributor
timestamp: June 06, 2021, 01:39:34 pm
content: I had assumed (silly me) that you were charging a 24V lead-acid battery bank as part of a solar power or off-grid power system. Charging any sort of lithium battery is a bit trickier and can be dangerous if something goes wrong. LiFePo4 batteries are a bit safer, but usually special purpose chargers are used. Do you have a link to something describing the exact batteries that you have? I would assume you have 8 in series for the voltage, but 280Ah seems impossibly huge for a scooter. If I know exactly what you have, I might have a better idea.

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 03:10:58 pm
content: Quote from: bdunham7 on June 06, 2021, 01:39:34 pmI have 8 cells.Each cell is an EVE cell.Each cell is a lifepo cell.Each cell is 280 amps.Each cell is 72mm thick, 205 mm tall and 175 mm wide.Each cell is called a 3.2 volt cell.Each cell can take up to 3.65 volts before damage.Each cell can go down to 2.5 volts before damage.Each cell is safe to operate to a high temperature of 35C.Each cell can operate safely down to - 18C.Not sure what else to add.They are 8 in series lifepo cells for 24 volts at 280 Amps per cell.Didn't know there was another way to say this.

author: bdunham7
author_rank: Super Contributor
timestamp: June 06, 2021, 03:38:31 pm
content: OK, I looked them up. That's an impressive battery pack! Is there a BMS (Battery Management System) that does cell balancing and protection?As for chargers, obviously you need all the current that you can get. You're limited to about 30A if you run it from a standard wall plug. The inexpensive 20A one I linked earlier may work, or there are these purpose-made 8S LiFePo4 chargers that might be better. I have no specific experience with either so I can't vouch for them personally. Batteryspace has been a decent vendor for me and they may be able to answer questions or make recommendations.https://www.batteryspace.com/smart-charger-15a-for-25-6v-8-cells-lifepo4-battery-pack---ch-lf24v15-pfc.aspxhttps://www.aliexpress.com/item/4000903076536.html?spm=2114.12057483.detail.3.26c14e5bBDSQFw

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 08:32:44 pm
content: Quote from: bdunham7 on June 06, 2021, 03:38:31 pmLOL heck no. You have to buy one of those separately. And I sadly got the Daly which is turning out to be crap.Thanks for being honest.Yeah even 20 amps would be fine. It takes me a week of casual riding to lose all the charge. And so a couple of days of charging is not too bad.Thanks for the links.Been trying locally to find a decent charger. But either the battery places don't do lithium. Or they sell things like the Longwei for $120.Nice fellow Canadians eh?EDIT: That second link looks like it might be a good one as they have dedicated chargers for lifepo.If anyone has had dealings with this company or these products, please speak up.Thank you.

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 08:53:58 pm
content: Quote from: bdunham7 on June 06, 2021, 03:38:31 pmThere is a guy named Steve that makes his own BMS that became popular. His company is called Overkill.While expensive as heck for me, I am going to have to save for a while and try to get one of his BMS's.Even if you screw it up you can send it back for a full refund. Now how good is that guarantee eh?

author: SherylinRM
author_rank: Contributor
timestamp: June 06, 2021, 08:58:26 pm
content: In case you wanted to know.The link for overkill ishttps://overkillsolar.com/He even has a redidit to try to answer peoples question as well.