Rec: end-current cutoff at low amps

[john61ct]

I'm looking for a device that will allow high charging current at 12, say over 100A, 500 would be nice, but will open/disconnect when amps drops to a low level. Failure mode should be open.

Ideally adjustable setpoint, but fixed at 1-2A would be OK.

Ideally handles 12-48V, but just 12 would be OK.

As robust and weatherproof as possible.

Some DIY would be OK.

Any relevant suggestions welcome.

[smac999]

I think the xantrax link pros had some programable outputs. Could maybe trigger at certain soc? Or maybe even amps? You'd have to look at manual.

Looks like it's only low soc, low voltage, or high voltage.

If it had high soc it may have worked.

[john61ct]

Comes to that, biggest possible Sterling DCDC B2B charger, apparently a 180A in the works.

Or some huge solar controller, catholic in its input acceptance?


But actually I was hoping for a single-purpose low-cost component.

[Ding Duck]

Wow, that's some serious power. What will be your supply volts?
My only other thought was if you get a traction battery charger manufacturer to supply the unit without the Transformer. Essentially just use the DC backend, but input volts will need to match etc
Cheers

[john61ct]

Originally Posted by Ding Duck

Wow, that's some serious power. What will be your supply volts?

Mainly an LFP house bank, so 13.8V, bit lower when not in active use, maybe up to 14 when loads are constant.

This specific use case is for an independent "catholic" intermediary between any "dumb" DC charge source and the batteries, will likely see shore power very rarely.

And will use with other nominal 12V specs for other lead-based banks, so the low-current cutoff point ideally should be adjustable.

I'm going to be looking at Arduino-based projects to drive relays, maybe learn how to adapt some open-source code.

A Trawler forum mentioned the "Smart Alternator Regulator" (not Ample Power's)

​http://arduinoalternatorregulator.bl...5/welcome.html

[barnakiel]

I believe some Victron stuff is programmable.

Start here:

https://www.victronenergy.com/upload...nfigure-EN.pdf

Then study around.

b.

[john61ct]

They have one-way BCD diodes, ACRs, "battery protectors" for loads etc, and of course their various charge sources, but haven't seen dedicated current-based relay controls from any of the mainstream vendors.

I think Victron doesn't even do DCDC chargers like Sterling/ProMariner/CTEK, which as I said is the closest category "off the shelf".

I'm thinking now, maybe more of a components / ham radio / electronics geek DIY thing, to get the big amps will likely need to trigger an external relay.

[Ding Duck]

John, this may be suitable? Would want to be sitting down when you get a price, but possibly the nearest out of the box solution?
Good Luck
Euro Options Schaefer Euro Cassette - Industrial | Powerbox

[john61ct]

Thanks, I appreciate the effort but sorry I don't see anything there.

As I said, if I need to go with an expensive powerful intelligent DCDC charger, I'm already looking at Sterling & co, at $500+

That category happens to include the functionality I'm looking for in this post, the same way someone looking for a portable cigar lighter could buy a Ferrari.

I guess I should have made explicit: single-function, robust, cheap as possible.

Like this:
https://www.kemo-electronic.de/en/Ca...rd-12-V-DC.php

or this

http://shop.pkys.com/Victron-BP220-B...-A_p_6423.html

just based on current rather than voltage.

[Ding Duck]

Originally Posted by john61ct

Comes to that, biggest possible Sterling DCDC B2B charger, apparently a 180A in the works.

Or some huge solar controller, catholic in its input acceptance?
.

Sorry, I thought you were looking for some type of charger. If you require just a switch as per these items you suggested below, then possibly use a 3pole Contactor (with 12VDC Coil?) and parallel the main poles. You could then potentially use a 100A Contactor to switch 300A. Need to take into account the DCxx Rating, the Ith and Max DC switching Voltage per pole. Using the Arduino kit you mentioned earlier as a interface relay to operate the contactor. Current sensing from a suitable Shunt and the OP Amp circuit to give you the resolution for 1-2Amps.
Alternatively, use the Arduino/ OpAmp option to act as a BMS Input into the Victron unit for open/ Close command.

Like this:
https://www.kemo-electronic.de/en/Ca...rd-12-V-DC.php

or this

http://shop.pkys.com/Victron-BP220-B...-A_p_6423.html

just based on current rather than voltage.

[john61ct]

Yes, exactly, I think I may need to start to learn how to start doing stuff at this level. Was an ICT guy in a past life, just need to get back on the horse.

Encouraging to know something related to Amps measurement exists already!

Thanks for the help, and sorry if my OP spec asking for such recommendations wasn't clear.

[Ding Duck]

This may be a simple solution to the current sensing side of the equation.
Have a look at the Allegro ACS758 / 759 Hall effect Current sensor. They do up to 200A in a combined unit, but options to go to 1000A. The 200A version is about $10 on ebay from China. Plenty of You Tube stuff on integrating these into Arduino.
All you have to do then is to decide on how your going to control the output.
Cheers

[Maine Sail]

Originally Posted by john61ct

I'm looking for a device that will allow high charging current at 12, say over 100A, 500 would be nice, but will open/disconnect when amps drops to a low level. Failure mode should be open.

Ideally adjustable setpoint, but fixed at 1-2A would be OK.

Ideally handles 12-48V, but just 12 would be OK.

As robust and weatherproof as possible.

Some DIY would be OK.

Any relevant suggestions welcome.

Nothing like this any longer exists in the marine market. The chargers used in the marine market, and most others, are voltage regulated not current regulated.

The reason for this is very simple. On boats or off-grid or RV we almost always have loads running while charging, be it from wind, solar, alternator, fuel cell or shore charger. Because of these house loads, and the fact that they are all CV based charge sources, using tail current as a primary means of charge transition to float or charge termination is not going to be safe on a large scale.

This is why charger manufacturers stick to CV regulation with egg-timers, "smarter" CV duration determination algorithms or even yer smarter algorithms with user controllable adjustments of CV duration, which can and may include tail current as a one of the data points, but not primary.

Charger makers, regulator manufacturers etc. are highly leery of moving towards current based transitions because it would require external shunts or current sensors and we all know how many shunts actually get installed correctly. It is simply a liability issue and most charger manufacturers I talk to don't want that kind of liability.

A land based charger maker sets charge termination at 5A for a specific battery eg; a floor scrubber machine. Crafty boat owner Darryl researches and buys one then installs it on his LFP bank on his boat. One day Darryl forgets, leaves the fridge on and goes home. The 5A charge termination current regulated charger now never shuts off. Because the fridge was drawing more than 5A, the charger stays live & never transitions, the battery cooks, burns boat and marina, and you guessed it the charger maker is the one that's going to be on the hook....

Heck even with just a single AC connection and two DC wires, plus grounding, I see chargers installed incorrectly all the time. The last manufacturer I knew of developing current based regulation, for the marine market, pulled the plug on it about 4 years ago. Liability.....

The other problem you have, other than the OFF trigger, point will be the ON trigger point. In an ideal world this would all be done via the charger and any BMS would just be additional insurance.

[john61ct]

Thanks for that detailed explanation RC!

I plan to have the Load circuits separate from the Charging buss, and several control points and monitoring points with shunts on each.

And will do my best to avoid being a Darryl, recognize my tendency to be too crafty 8-)

And paying an expert pro for advice where necessary, and definitely safety surveys after major changes, are part of the build strategy.

Possibly including if needed a hold-harmless note releasing him from liability. I hear there's a good outfit up in Maine 8-)

[a64pilot]

I know my Magnum inverter charger is able to be set to drop out of Absorption to float at a set number of amps.
However I believe it then drops into float, I know you want off, but if you set float voltage low enough, would that be acceptable?