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Discussion Starter #1
Looking to get a dc to dc charger so I can charge my 72v prowler ev is (golf cart) from by 24v battery bank. Without converting to AC then back to DC. Anyone know of a product?
 

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Exactly what batteries?

And do you need termination to be automatic, or can you stand by, keep an eye out and turn it off once full?

Really no availability of shore power?

What is the 24V energy source?
 

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Discussion Starter #3
My RV is 6 24v battleborn batteries in parallel. The cart will be 6 12 volt Dakota batteries in series.

I would like the termination to be automatic. Shore power is generally not available unless I am running my generator. This is really my 5th wheel with an electric utv to ride around in.
 

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Gensets do produce nominally the same **type** of AC power as shore (grid, utility), but of course at 100x the cost, plus noise, hassles fetching fuel etc.

So are you saying you want to charge your batteries by running the genset for 7+ hours a day?

In which case no DCDC is needed, just two different mains chargers running concurrently.
 

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Or you could set up intra-connections to series-parallel three pairs to make everything 24V, each cycle, then back to 72V.

All that does is save the cost of the 72V mains charger.
 

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Discussion Starter #6
No. I do have the genset and a solar array. Just direct dc to dc simply because I can charge quicker and with more efficiency than running an AC charger. I do like your 24 volt parallel interconnection idea.
 

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Or you could set up intra-connections to series-parallel three pairs to make everything 24V, each cycle, then back to 72V.

All that does is save the cost of the 72V mains charger.
... and an inverter, since "mains" power is not available.

The original idea of a DC-to-DC charger is the straightforward solution, although it won't be cheap - if you can find it at all - since it's not a common output voltage for DC-to-DC chargers.

The next simplest solution (without reconfiguring the pack to 24 V) is any suitable AC-powered 72 V charger (not just a constant-voltage converter, but a charger programmed appropriately), and a 24 V input inverter of sufficient capacity to power it. The efficiency will be lower than an integrated DC-DC solution, but in an RV with substantial 24 V DC capacity I would want that inverter for convenience anyway.
 

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Yes, an inverter may still be needed if mains loads are needed while the genset isn't running.

But the source 24V input is coming from what?

I hope no one is thinking about pulling from the 24V bank without an actual energy input active, and a powerful one at that, really should be high enough to prevent any energy being pulled from the bank, that should just act as a buffer.

No. I do have the genset and a solar array. Just direct dc to dc simply because I can charge quicker and with more efficiency than running an AC charger.
I think not the case, or at least can't see how.

Given that you need a proper charger - automatically terminating when the bank is full

afaik that is only available powered from the AC output of the genset.

Grin Satiator is an excellent choice, and very flexible, although limited to 360W can be stacked in parallel and current user-adjusted,

in order to make most efficient use of your genset's current output, depending on what other loads may be concurrently drawing.

model# 7205 can be adjusted for nominal "36V-84V" @4-5A

#2415 is for "12-24V" max output 36V @15A
 

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You may be able to find "boost" solar controllers that can charge at nominal 72V.

A lower voltage input to the SC may be possible from a mains PSU or charger from the genset when insolation conditions are not sufficient.

In effect acting as a DCDC charger.
 

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Discussion Starter #10
Thanks all. Yes Brian My issue is finding a 24V input and 72V output. I do have an invert plenty big (Parallel victron 3000 multip with a 72v Quiq Charger and that works okay. I just waste a lot of AH going DC-AC-DC. And it’s output is only 17A.


John61ct- yes I am talking about pulling directly from the 24v bank (through a programmable DC / DC charger.) Looking to push about 50Amps into the 72V bank which is .5C
 

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yes I am talking about pulling directly from the 24v bank
50A at what voltage? Best to use Wh in this case with circuits at different voltages.

Unless you have an actual charge source

e.g. alternator, generator + mains charger or solar (amps output?)

supplying that power to the 24V side, just using that bank as a buffer, you would be wasting a **very** large percentage of that power, much more than running DC-AC-DC through a decent inverter.

> through a programmable DC / DC charger

Pretty sure does not exist.

Also note, lead batteries will take seven hours at best to get to 100% Full, which is required for longevity, at least most cycles.

And 0.2C is likely the highest CAR that bank can manage, even in the early Bulk stage, and then it will rapidly decline.

Link to the specs?
 

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OK, so "Dakota batteries" are also LFP?

If so, ignore the CAR issue above.

Wow, even if you don't care about the inefficiency, going from bank to bank will require some major current-limiting circuitry.

Look for 24-24V DCDC try Sterling.

Then the switching-infra wiring from 72V to 24V layout will keep costs reasonable.

But really, powering a 72V nominal mains charger from the genset is the way to go, since that's how you're refilling the 24V bank as well.
 

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It's not accurate, but my rule of thumb is that we lose at least 10% energy in heating losses when we swap one voltage/process for another. I sure get why the OP wants to skip as many intermediate steps as possible.




I hope that others have had more luck with these boost modules than I have had.

I made up 120VDC LA battery bank, then would split to charge. They come in several configurations, and I feel that I've been burnt by at least a dozen over the last 5 years or so.

It's never been an easy to find, desolder, replace type of fix. I assume that the problem is in the ICs. It may seem that there is something wrong with my setup to continue to have similar failures. I have a decent background in electrics and electronics, and work pretty regularly with batteries and different types of chargers and charging.

I tried these with slightly-above-trickle currents and up to 10 amps, same result.

I switched back to a big forklift charger for split-bank charging, then finish off with a DIY capacitive charger for an equalizing charge.

That doesn't satisfy the original requirements of direct 24DC to 72DC, but that's what I finally had to do to get a reliable set up.

Please do share if you find a solution that lasts. I'd love to hear about it. Thanks.

Mike
 

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Run the genset.

Charge the 24V and 72V banks concurrently, or prioritize the emptier one if its charger can take all the genset output.

Grin Satiator(s) are great for the 72V, but there are cheaper Chinese-direct from Ali units that will be OK if you don't want to pay the extra for full adjustability and likely better longevity.

Sorry if I missed it, but why do you think going from one bank to another without an active source is practical?

What are the kWh capacities involved?
 
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