Please recommend a quality 12V lead acid battery tender that's not too RF noisy - Page 1
Forum section: electronics / projects

author: Jester
author_rank: Frequent Contributor
timestamp: March 03, 2022, 02:21:37 pm
content: Application is to charge a 7A/hr 12V lead acid battery that will be the supply for a LoRa transceiver, so I want to avoid chargers that are either RF noisy or unsafe.Edit: OTS (Off The Shelf)Can anyone recommend something decent?Thanks,J

author: cdev
author_rank: Super Contributor
timestamp: March 03, 2022, 02:37:31 pm
content: You might need to fix the RFI yourself. Ive done it.Use of the appropriate ferrite materials and if that's not enough, bypass caps.

author: tunk
author_rank: Super Contributor
timestamp: March 03, 2022, 02:48:21 pm
content: An old fashioned charger with a transformer, rectifier and smoothing capacitor?You may be able to find something designed for small/motorcycle batteries.

author: SeanB
author_rank: Super Contributor
timestamp: March 03, 2022, 05:10:00 pm
content: You still get linear chargers for these batteries, normally used in the security industry, and they come in 1A and 2A versions. Normally need a 14-16VAC supply to operate, and have basically a bridge rectifier, smoothing capacitor and 1 or 2 LM317 regulators as active device, with a small pot to adjust output voltage, and a connector for the battery.

author: TheMG
author_rank: Frequent Contributor
timestamp: March 03, 2022, 07:29:55 pm
content: I would just use a linear regulated power supply, adjust the voltage for the correct float charge level for the battery.Most of the small battery tenders (and even larger batteries chargers too) you're likely to find at least on the consumer market these days are likely to be SMPS and with just the bare minimum EMI filtering to pass regulations (if it even passes at all, some are quite questionable).

author: tautech
author_rank: Super Contributor
timestamp: March 04, 2022, 12:48:29 am
content: Quote from: SeanB on March 03, 2022, 05:10:00 pmYep, piss easy to make and with their inbuilt protection you don't even need heatsink them.Veroboard, small bridge, tranny, some protection diodes, resistors, caps and a miniature 10 turn trimmer.....done !

author: MarkF
author_rank: Super Contributor
timestamp: March 04, 2022, 02:36:47 am
content: Quote from: tautech on March 04, 2022, 12:48:29 amHere is that circuit from the web:Three choices of resistors (in red) and their charging currents and voltage set pot (in blue).

author: tautech
author_rank: Super Contributor
timestamp: March 04, 2022, 02:52:16 am
content: Yeah nice touch adding an extra bipolar and LED for power indication however an extra diode in series with the battery is a good idea too.

author: Jester
author_rank: Frequent Contributor
timestamp: March 05, 2022, 01:24:11 pm
content: I updated my original post, to state: Off the shelf.You would think that someone must sell a small say 500ma or 1A linear wallwart type supply?I see Tripp Lite offers smaller 12V linear supplies aimed at the CB and HAM radio market, however they state not suitable for battery charging and they are not exactly cheap at about $80.You would think a safe low cost 10VA linear wall wart type supply would have enough of a market to support such a product. I must be really bad with my goggle search efforts.

author: tunk
author_rank: Super Contributor
timestamp: March 05, 2022, 01:36:34 pm
content: Would this work:https://www.princessauto.com/en/12v-automatic-float-charger/product/PA0008729188

author: Jester
author_rank: Frequent Contributor
timestamp: March 05, 2022, 02:24:16 pm
content: Quote from: tunk on March 05, 2022, 01:36:34 pmI think this would very likely qualify as RF noisy

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 05, 2022, 03:53:27 pm
content: Quote from: Jester on March 05, 2022, 02:24:16 pmIf it uses a linear wall wart, there should be no problem. Assuming there's a problem in the first place, that is. LoRa is well into the UHF band (unless you have a nonstandard implementation on a lower band) which is not likely to get interference from switching power supplies. Also, wouldn't there most likely be a switching regulator on the board?

author: Jester
author_rank: Frequent Contributor
timestamp: March 05, 2022, 04:32:48 pm
content: Quote from: NiHaoMike on March 05, 2022, 03:53:27 pmI doubt that Princess Auto charger is linear.The 5V on board regulator on my board is actually linear. You might be right 450MHz is a long way from a good switch mode, but perhaps not far enough from the harmonics of a cheap as dirt and non FCC compliant junk power supply that seem so prevalent these days.On a side note we recently had our garage door opener replaced and the installer stated that they NEVER use LED bulbs in the overhead unit because they have such a noticeable impact on sensitivity. I’m pretty sure they operate around 450MHz. I guess the receive signal is limited with the typical coin cell transmitters.

author: tunk
author_rank: Super Contributor
timestamp: March 05, 2022, 05:10:35 pm
content: The size (from the photo) and weight (0.8lbs) suggests that it's linear.

author: Jester
author_rank: Frequent Contributor
timestamp: March 06, 2022, 12:17:22 pm
content: Quote from: tunk on March 05, 2022, 05:10:35 pmtunk, good eye, you are correct.The float voltage is 13.0V up to about 100ma, above that current it becomes obvious this is not a switcher. Looks like they are using a single diode for rectification.This is what I was looking for, did not expect to find one so close to home.In the link you provided they did not have a close up of the wall wart part or label, the actual unit is labeled Input 120Vac (not universal input)This appears to be the Canadian available equivalent of the $10 Harbor Freight chargerhttps://www.harborfreight.com/automotive/battery-tools-accessories/battery-chargers-maintainers/automatic-battery-float-charger-64284.htmlFrom the reviews, it seems if you get a good one (90+%), they are trouble free for years and years, if you get a bad one, throw it away.Thanks, this is what I was looking for.

author: Circlotron
author_rank: Super Contributor
timestamp: March 06, 2022, 12:25:17 pm
content: Proper float voltage is 13.65 @ 20 deg C.

author: Jester
author_rank: Frequent Contributor
timestamp: March 06, 2022, 12:41:41 pm
content: Quote from: Circlotron on March 06, 2022, 12:25:17 pmUnderstood, looks like the $10 charger is not temperature compensated and was designed to be safe at higher temperatures. This is actually ideal for this application because it's going to Texas, so the float voltage might be on the low side in winter but close to ideal in summer.

author: cdev
author_rank: Super Contributor
timestamp: March 07, 2022, 09:05:37 pm
content: I have two Centech 69955 models that look identical with only two very minor cosmetic differences.. And they were both very RF noisy.Radiating lots of HF+VHF noise. The (almost, there still is a bit of noise) "cure" was wrapping the power and output leads around two large ferrite beads, each, using a total of four big ferrite beads per charger.Quote from: Jester on March 05, 2022, 02:24:16 pm

author: Cicada
author_rank: Regular Contributor
timestamp: March 08, 2022, 05:47:17 pm
content: Here is a linear charger.https://www.ti.com/lit/ds/symlink/uc2906.pdfThere are not many such solutions today.Switch mode ones can be noisy if you don't handle them properly if that is possible at all.

author: Jester
author_rank: Frequent Contributor
timestamp: March 08, 2022, 07:03:50 pm
content: Quote from: cdev on March 07, 2022, 09:05:37 pmWell that’s interesting, they look similar to the Princess Auto one in the link from tunk. The princess auto variety are definitely linear (see the waveforms in my previous post), so no RF.That’s odd because the image I found for the 69955, appears to use the same linear wall wart ( rated 120Vac), not 85-250V. I’m wondering if Centec changed their design to now use a switcher?Do you recall what frequency the Centec was radiating?