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Old 31-07-2020, 16:30   #1
er9
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ACR or DC to DC charger?

im in the early stages of contemplating my electrical upgrade. iv'e only made a decision on my shore charger so far (Sterling ProCharge Ultra)


My original plan is two banks, a house and a small start bank. My itention is to direct all charging sources to the house bank and then trickle charge the start bank via an ACR. Since iv'e learned a bit more about DC to DC chargers i and am now wondering if a DC to DC charger would be a better option?



reason being I havn't decided yet on batteries or type for the house bank. I'm leaning towards Fireflys a tthe moment but keeping the FLA's for the start batteries. Being two different chemistries requiring different voltages would i be better off using a DC to DC charger between the banks so i can program the voltage settings for the start bank chemistry individually or would an ACR still suffice?


it seems like a nice option to be able to mix chemistries between banks.
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Old 01-08-2020, 09:35   #2
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Re: ACR or DC to DC charger?

The 14.4v for fireflys is perfectly ok for flooded starter as well.

Either will work fine.
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Old 01-08-2020, 09:56   #3
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Re: ACR or DC to DC charger?

Well you won’t trickle charge with an ACR, you will charge at whatever rate 14.4V gives you, current limit will only be what the charge source can provide, but as the start battery should always be highly charged, it shouldn’t draw much current, lead acid batteries self regulate current draw by acceptance rate.
Automobiles output 13.8 to 14.2V continuously, they are only single stage, and of course automotive start batteries last about 5 years on average. 14.4 is a little high, but not by much, or may cause you to add water a little more often should be the only down side.
Technically a DC to DC charger would be better, but an ACR will be fine.

You will be overcharging the start battery, but it should tolerate it as it’s not a severe overcharge, and well start batteries aren’t real expensive things anyway.
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Old 01-08-2020, 10:50   #4
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Re: ACR or DC to DC charger?

DC-DC charger for change of chemistry (eg LFP house bank and AGM start). ACR for connecting between banks of similar chemistry - Firefly to FLA would probably qualify for enough of a change. If you went AGM for start, you'd probably be okay with ACR as I believe the Firefly is very close to AGM.

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Old 01-08-2020, 11:06   #5
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Re: ACR or DC to DC charger?

If I'm not mistaken, the ProCharge Ultra has outputs for two banks. Just hook the second bank output to the start batt and Bob's your uncle. No need for either ACR or batt2batt.
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Old 01-08-2020, 11:21   #6
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Re: ACR or DC to DC charger?

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If I'm not mistaken, the ProCharge Ultra has outputs for two banks. Just hook the second bank output to the start batt and Bob's your uncle. No need for either ACR or batt2batt.

i was just thinking the same thing. the 60 Amp version has three outputs. I was wondering why i couldn't just use a second output from the charger to the start bank and use a battery chemistry module (Sterling Power) in the line to the start bank. this way i could set the voltages into the house bank and start bank independent of each other.



my understanding of all of these devices and how they all work together is still a little fuzzy though so still trying to wrap my head around it all.
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Old 01-08-2020, 11:46   #7
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Re: ACR or DC to DC charger?

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If I'm not mistaken, the ProCharge Ultra has outputs for two banks. Just hook the second bank output to the start batt and Bob's your uncle. No need for either ACR or batt2batt.
That only works when the shorepower charger is used, it doesn’t work away from the dock unless a generator is running.
Assumption is that a charging solution is desired when motoring or when Solar is charging.

The ACR will work and is likely the least expensive option. I have never heard of the Sterling module, but bet it’s essentially a DC to DC charger, what else could it be? But it only works with shorepower, and that alone makes it less than optimum
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Old 01-08-2020, 11:58   #8
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Re: ACR or DC to DC charger?

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my understanding of all of these devices and how they all work together is still a little fuzzy though so still trying to wrap my head around it all.
An ACR is simply a combiner, it connects banks whenever voltage is above a certain point, Usually higher than the resting voltage of a fully charged bank of course, but it simply connects two banks, it’s an on and off switch is all.

A DC to DC charger is a charger, more advanced and needed when voltage requirements are significantly different.

A Firefly is an AGM battery, for example firefly wants 14.4 absorption voltage, Lifelike wants 14.3 +or- .1 so 14.4 is fine.

But also remember that it’s not really as critical as we want to make it, not for a single simple starter battery, for instance you can put either a flooded or an AGM battery in an automobile, adjust nothing and either works fine.
The automobile works at a voltage above float but below absorption. You only really need three stage charging when deep cycling, and when your trying to recharge as fast as possible without harm But starter batteries will live a long life at something around 14V + or - .5v or so, and of course a starter battery should never be deep cycled
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Old 01-08-2020, 12:06   #9
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Re: ACR or DC to DC charger?

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That only works when the shorepower charger is used, it doesnít work away from the dock unless a generator is running.
Assumption is that a charging solution is desired when motoring or when Solar is charging.

The ACR will work and is likely the least expensive option. I have never heard of the Sterling module, but bet itís essentially a DC to DC charger, what else could it be? But it only works with shorepower, and that alone makes it less than optimum

interesting i wasnt aware of that.



initially the charge source will be solely shore power but i would be adding a Sunpower 350 watt panel to an arch a year or two down the line, and eventually more solar if/when i can figure out where to add it, possibly a hydro generator in the far future.
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Old 01-08-2020, 12:13   #10
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Re: ACR or DC to DC charger?

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An ACR is simply a combiner, it connects banks whenever voltage is above a certain point, Usually higher than the resting voltage of a fully charged bank of course, but it simply connects two banks, itís an on and off switch is all.

A DC to DC charger is a charger, more advanced and needed when voltage requirements are significantly different.

A Firefly is an AGM battery, for example firefly wants 14.4 absorption voltage, Lifelike wants 14.3 +or- .1 so 14.4 is fine.

But also remember that itís not really as critical as we want to make it, not for a single simple starter battery, for instance you can put either a flooded or an AGM battery in an automobile, adjust nothing and either works fine.
The automobile works at a voltage above float but below absorption. You only really need three stage charging when deep cycling, and when your trying to recharge as fast as possible without harm But starter batteries will live a long life at something around 14V + or - .5v or so, and of course a starter battery should never be deep cycled

thanks. that must be why i see ACR's spec'd so often in wiring diagrams by people who know what they are talking about -vs- DC to DC chargers. the ACR is attractive also as its 1/4 the price of the DC to DC charger.



the reality is im most likely going to have either all FLA's or a combo of AGM/FLA's for the next decade give or take until lithium becomes more mature and the prices drop some. so it sounds like i shouldnt be overly concerned about that combination.
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Old 01-08-2020, 12:24   #11
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Re: ACR or DC to DC charger?

I recently rewired my boat for long term cruising. Went with LFP for house bank and AGM for engine start, generator start, and bow thruster/windlass. Frankly, did not make financial sense to go LFP for point loads, and LFP is not particularly good for engine start as the BMS is typically programmed to throttle CCA. And then there is the cost differential.

I went with a DC-DC charger between them. I have dual Balmar alternators charging for about 200 amps rating, plus ACRs between the AGM banks to isolate the engine start battery. As A64pilot said, this is for underway - using a multi-bank battery charger has two issues. First, it requires an AC input (shore power or generator). Second, not all muti-bank chargers are created the same. From memory, the good ones are worth the extra money as they truly isolate the batteries. But it is a steep premium.

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Old 01-08-2020, 13:29   #12
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Re: ACR or DC to DC charger?

Well, just for a simplicity point of view, I'd skip either the ACR or the DC-DC charger.

Just install a Off-1-both-2 battery switch. Hook the house battery to "1" and the engine battery to "2". You just leave that switch on "1" most of the time, and put it on "2" occasionally to make sure that battery is still charged.

Hook your charger (and alternator output, and solar output) to the load side of the switch and you can direct all charging to either batteries or both.

No extra electronics, no extra wiring.

BUT, you have to manage it yourself. No black boxes, no automation.
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Old 01-08-2020, 13:30   #13
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Re: ACR or DC to DC charger?

I’m nearly certain that my Sterling Pro Charge Ultra has three charge outputs, I’m also nearly certain that they in fact are really just three wires with diodes connected to a single output, the only thing they add to a single output is the diodes.
It will not push more power to a higher discharged bank or any of that, the bank if an LA bank will do that automatically, thats how lead acid banks work, the lower the SOC, the greater current it will accept.

So most chargers with multiple charge points, aren’t really what a lot of people think they are. The diode prevents a discharged bank from discharging a more highly charged bank when the charger is off, other than that it’s just one charger.
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Old 01-08-2020, 17:21   #14
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Re: ACR or DC to DC charger?

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Well, just for a simplicity point of view, I'd skip either the ACR or the DC-DC charger.

Just install a Off-1-both-2 battery switch. Hook the house battery to "1" and the engine battery to "2". You just leave that switch on "1" most of the time, and put it on "2" occasionally to make sure that battery is still charged.

Hook your charger (and alternator output, and solar output) to the load side of the switch and you can direct all charging to either batteries or both.

No extra electronics, no extra wiring.

BUT, you have to manage it yourself. No black boxes, no automation.
I dont like that arrangement. That's what I have now and it's a pain to manage. I'd prefer to automate it and not have to think about. I'm sure it will be way more efficient than me at managing the charging schedule. When I get to the boat all I'll have to do is turn on the power and it's all taken care of. Now if I could just get a phone app to do it all from half way around the world and deliver my boat remotely, fully automated...
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Old 01-08-2020, 17:45   #15
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Re: ACR or DC to DC charger?

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I dont like that arrangement. That's what I have now and it's a pain to manage. I'd prefer to automate it and not have to think about. I'm sure it will be way more efficient than me at managing the charging schedule. When I get to the boat all I'll have to do is turn on the power and it's all taken care of. Now if I could just get a phone app to do it all from half way around the world and deliver my boat remotely, fully automated...
Well of course. Almost everyone wants to let the little blackboxes take care of their battery charging and I don't expect to change anyone's view.

I just have to keep putting my opinions about simplicity and self reliance out there, if for no other reason that to let some people know they CAN think outside of the box.

By the way, I know that your wish for automated boat tending, with an App, from around the world, was tongue in cheek, but think about the implication, would you really rather have an automatic boat sailing by itself while you sit on your couch? Why not just give up the boat and watch You tube videos?
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