Suggestions for large 24V charger (like 80A DC charge or more?)

daveola · July 29, 2019, 02:37:16 PM

Has anyone used Powermax chargers? The amazon reviews make it sound like they fall apart if they work at all, but I've seen these at a great price. Probably one of those "too good to be true":

https://www.amazon.com/Powermax-PM3-50-24LK-Power-Supply-Converter/dp/B01NBRCA85/ref=sr_1_1?keywords=powermax+24v&qid=1564435997&s=gateway&sr=8-1#customerReviews

50A at 24V for $250?!?

stevet903 · July 30, 2019, 05:10:41 AM

Here's an Iota 40A for $213

https://www.solar-electric.com/iota-engineering-dls-27-40-x-battery-charger.html

Seems to have good reviews.

daveola · July 30, 2019, 12:22:13 PM

That looks like it might be my solution!

Does anyone know if I can run it in parallel with my SW4024 charger if I have two separate AC voltage sources?

It would be nice if there was a way to also selectively limit the input to 15A (30A VDC output) for when I only have a NEMA 15A outlet to plug into, but I don't think that's an option with this charger.

bevans6 · July 30, 2019, 02:50:46 PM

Two separate AC sources are irrelevant to the charging function, the chargers don't care. You can run chargers in parallel at the same time if they are not "smart" chargers. If they are, they tend to fake each other into thinking the bank is fully charged when it isn't. Remember that you can have a charger with infinite ampacity, but if you don't have a load that needs the current, it won't flow. You mention you have a large battery bank and AGM batteries - while they can accept a high charge rate, they don't need it. One thing is that you have links to both "chargers" and "converters". In the RV world a converter is often optimized to supply steady 13.6 volt source to house loads, and oh by the way charge the batteries. A charger is optimized to charge the batteries, and can supply quite high voltages to do it - enough to piss off some common house loads. The two are not equal.

I must have missed it - how big is your battery bank, and are they indeed AGM batteries? What type?

peterbylt · July 31, 2019, 11:30:16 AM

Quote from: daveola on July 29, 2019, 02:37:16 PM
Has anyone used Powermax chargers? The amazon reviews make it sound like they fall apart if they work at all, but I've seen these at a great price. Probably one of those "too good to be true":

https://www.amazon.com/Powermax-PM3-50-24LK-Power-Supply-Converter/dp/B01NBRCA85/ref=sr_1_1?keywords=powermax+24v&qid=1564435997&s=gateway&sr=8-1#customerReviews

50A at 24V for $250?!?

I have the smaller version, PowerMax PM4 45A 110V AC to 12V DC 45 Amp.

https://www.amazon.com/PowerMax-PM4-55A-Converter-Battery/dp/B01ER3LH3O/ref=sr_1_fkmrnull_2?keywords=PM4%2B55A&qid=1556659129&s=gateway&sr=8-2-fkmrnull&th=1

When I bought new start Batteries, I moved the old 8D's to be my temporary house batteries (a year ago), this Power supply/ charger, works great, keeps the batteries charged and supplies all the 12-volt power I need for the lights and water pump.

Will probably need to upgrade the batteries when/if I get an Inverter.

Peter

daveola · July 31, 2019, 01:43:02 PM

Quote from: bevans6 on July 30, 2019, 02:50:46 PM
You can run chargers in parallel at the same time if they are not "smart" chargers. If they are, they tend to fake each other into thinking the bank is fully charged when it isn't... One thing is that you have links to both "chargers" and "converters"... I must have missed it - how big is your battery bank, and are they indeed AGM batteries? What type?

1) Good point - so I probably can't use one of these with the charger in my Trace SW4024 at the same time. I'll probably just try to find a large enough single charger to do the work then

2) Also a good point - I'm looking for a charger, not a converter, so I'll have to pay more attention to that

3) The bank is quite large and indeed AGM. I have 10 group 8D AGM batteries, which I believe can take somewhere between 60-80A during bulk, though I admit it's been a bit since I did the math on that. I do know that my SW4024 often maxes out at it's 31A max charge.

Gerry H · July 31, 2019, 03:30:01 PM

I have had an Iota DLS 27-25m w/IQ-4 on my starting batteries (4 group 31) for almost 10 years and no problems, I'm quite happy with it and would highly recommend this company. I also have an Iota DLS-55 13.4V @55 amps on my 12V house system. These may not be the best out there, but are cost effective and so far reliable. The best will cost more $. Iota has done the job for me at a good price and I would buy again if they fail and they all will fail at some point.
Best of luck. Gerry H

bevans6 · August 01, 2019, 05:36:54 AM

Going from the Trojan data sheet for 8D AGM dual purpose batteries, they are 230 AH @20 hr. The maximum bulk charge rate is 20% of that, so if you have 10 batteries in series/parallel for 24 volts, you have 1150 AH @20 hr so the maximum absorption charge rate is 230 amps at 28.8 volts. Which is a lot of amps. That's 6624 watts, or 55 amps at 120 volts AC before losses. The question is - how often will you drain your house bank to the point that it will draw that kind of current? And for how long will it draw that? The answer is it will switch to absorption charging as soon as the bank reaches a pre-set voltage limit (in the example, 28.8 volts), and at that point the charging is current limited. The bulk charge stage might only last 10 minutes before it starts absorption charging and the charge current is dropping.

Bottom line is you ain't gonna get too large a charger, and if anything you'll be limited by the power you can put into a charger. Lower capacity chargers will increase the bulk time, and absorption will take longer as well because it will initially be limited to the maximum the charger can put out, not the regulated current limit of 20% of capacity.

Bulk charging is variable voltage, current limited charging. In this example, a battery bank at 50% SOC would start out at 24.5 volts, and be charged at 230 amps until the battery voltage reached 28.8 volts.

Absorption charging is constant voltage, variable current charging. In this example, as soon as the battery bank reaches the set point of 28.8 volts, voltage is kept constant at that level and current begins to fall as the battery absorbs the energy and "pushes back" at the charger. In a realistic scenario, with a 50 amp charger the voltage will sit at 28.8 volts and 50 amps for a decent period of time as the battery bank catches up to the capacity of the charger, and thein current will fall off to a couple of amps. As soon as the current falls to a set point, the charger switches to Float charging.

Float charging is when the battery bank has reached 100% SOC, or very near that. It is constant voltage, variable current, with the voltage set to 27.2 volts. Charge current will vary, but will be very low.