On Sun, Mar 20, 2022 at 3:34 PM EV List Lackey via EV <ev@lists.evdl.org> wrote: > > It sounds like your charger has an electrolytic capacitor across its output. > > Could you add a precharging circuit across the contactor?
I thought of this but wanted something as simple as possible. Of course, a diode has heat dissipation to consider and who knows how long it will last. I have more responses about this idea after Lee Hart's email below. I like Bill D's suggestion of the 5-pin connector for its simplicity. I just haven't found a 5 pin connector yet so I think I'll stay with the NEMA L6-20 I have and work on some sort of pre-charge. On Sun, Mar 20, 2022 at 5:11 PM Alan Arrison via EV <ev@lists.evdl.org> wrote: > > Wouldn't the voltage drop confuse the charger, especially when it gets > to the constant voltage point near end of charge? I need to verify what voltage the internal BMS starts to balance but I think it is still before the ending voltage the battery will see. On Sun, Mar 20, 2022 at 5:54 PM Matt Lacey via EV <ev@lists.evdl.org> wrote: > > The charger won't know about the voltage drop, it would just reduce the > CV voltage by 0.7V or so > > The bigger problem is the charger may not start, if there's no voltage > present on it's output. Many of these batteries' BMS will cut off the output so the voltage across the terminals is 0V. Because of this, the chargers need to attempt to charge even with 0V on the output. This is why I purchased the Dakota Lithium charger. I now wish I had hunted for a soft-start charger. On Sun, Mar 20, 2022 at 9:32 PM Cor van de Water <cor.vandewa...@gmail.com> wrote: > > David, > Why are you unplugging the charger? I'm mounting the charger in the golf cart. It doesn't always go back to the same place on the campus it is used on so it needs to be able to charge wherever it is at. I have an extension cord with a NEMA L6-20 plug on the end so the extension cord isn't "borrowed" for other uses and can remain in the golf cart, and so the plug can handle more plug-unplug cycles. I also don't want a standard extension cord used in case the end is worn out and causes something to melt or catch fire. The smaller battery than the lead-acid pack leaves a nice storage space under the seat for it. Also, the documentation specifically states to not leave it plugged in and connected to the battery for more than 16-24 hours after the charge is finished. This is, I'm sure, just to make the charger cheaper to make. If your question was about why I'm disconnecting it from the battery pack, David Roden is correct. It is due to the constant 0.12A drain on the battery when it isn't hooked up to AC power. On Mon, Mar 21, 2022 at 10:08 AM Lee Hart <leeah...@earthlink.net> wrote: > > > Hi David, > > I'm emailing you directly because the EVDL no longer accepts posts from > Earthlink. I'm still around and reading it! I just can't post to the EVDL. > > It's fairly common for poorly designed chargers to put a constant load > on the battery. They need to monitor the battery voltage anyway, so it > saves money to "borrow" the battery voltage to also power the charger's > electronics. They assume that the charger will always be plugged in; so > it will be "maintaining" the battery once it is fully charged. > > David Roden had the right idea to fix this. Add a relay with a 120vac > coil, and a contact in series with the charger's output. When AC is > applied, it pulls in the relay, which connects the charger to the pack. > > But as he says, the output circuit of the charger must have a big filter > capacitor that draws a high peak current if you immediately close the > output relay. The fix for this is to include a "precharge" or "inrush" > limiter. The simplest way to do this is with TWO relays. > > Relay#1 is a small relay with a 120vac coil and a low-power NO (normally > open) contact. Its coil is across the AC input to the charger, so it > pulls in when the charger gets AC power. Its contact has a resistor in > series, connected between your pack and the charger output. The resistor > is chosen to provide 0.1 to 1 amp to "charge up" the output circuit > inside the charger. An old-style tungsten light bulb is a convenient > resistor, and also indicates that the circuit is working. :-) > > Relay#2 is a power relay, with a coil voltage to match your pack > voltage, and a contact good for 15 amps or more. If your golf cart has a > 48v pack, then use a relay with a 48v DC coil. Or, you can use a 24v DC > relay with a resistor in series with its coil so it sees 24v when "on". > Relay#2's coil (and its series resistor, if needed) connect across the > charger's output; so it will be "on" when the charger is operating. The > contact of relay#2 connects the battery pack to the charger output, thus > shorting out relay#1's contact and precharge resistor. > > Here's how it works: When the charger has no AC power, both relays are > off. When you connect AC to the charger, it also pulls in relay#1. Its > contact connects the precharge resistor from pack to to charger output, > thus gently charging up the charger's output capacitor and control > circuit. When the charger's output voltage gets high enough to start > charging, it also turns on relay#2, to short out the contact of relay#2 > and its precharge resistor. From this point, normal charging takes > place, with no loss in a series diode. > > Hope this makes sense! > Lee Hart I think I follow what you are saying and if I do, this is simpler than finding a time delay relay. Let me see if I have it: 1) Charger and Relay #1 get AC power at the same time. The contacts of Relay #1 connect the precharge resistor. 2) The coil of Relay #2 is across the output of the charger. When the charger starts or the precharge increases the voltage sufficiently, Relay #2 pulls in, shorting out the precharge resistor. Hopefully there is a long enough delay in the charger starting up. I'll have to time this and see. Since Relay #2 is held in by the charger/battery voltage, what will release the relay when charging ends since the battery voltage will back feed the coil? I guess relay #1 could be a double pole with one pole in series with the coil of Relay #2. Thanks for the responses so far. David D. Nelson _______________________________________________ Address messages to ev@lists.evdl.org No other addresses in TO and CC fields UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub ARCHIVE: http://www.evdl.org/archive/ LIST INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
