Blue Sea ACR and DC to DC Charger?

[Srpat]

I've been scratching my head on how to charge my batteries in my F550 shuttle bus. Planned set up is 4-600 amp hours of 6v golf cart batteries.

F550 has dual alternators that have the possibility to push a lot of amps, so the only ACR I could find was the ML series from Blue Sea that are good for 500 amps. However, it seems like the ACR will not fully charge batteries because it is not a smart battery charger.

I am considering two options. One, a small solar system that has a smart battery charging profile I like built in to the controller. Or two, an additional 10 or 20 amp dc to dc charger in addition to the ACR. But I can't find anybody that's done that before.

 

[VerMonsterRV]

First off how large are the alternators? Wet cell batteries will only accept a certain amount of charge so if you have a 100 amp alternator and a 400 amp hour battery bank (or even 600) then just wire the second alternator right to the house bank. Too high of a charge rate will damage (boil) wet cells (from the Trojan website, they list 13%). Now if you were to go to LifePO4 then all this changes as they can accept a much higher rate of charge.

You can also go with an alternator without an internal regulator and get a external multistage regulator. We did this for years on our sailboat using Balmar (crazy expensive though) gear. A good alternator shop may be able to modify your current alternator to remove the internal regulator, so that an external multistage could work. Here is a link to Defender (marine supplier) for smart regulators (there are others out there also, we also used one from Sterling). If you go this route I would try and mount the regulator in as dry/cool spot as possible to extend the life. I see now that Victron uses the Balmar products for alternators, I can say Balmar alternators are expensive but we have never had one fail.

One word of caution though, a smart regulator will put way more stress on the alternator. If your batteries are low it will ask the alternator to go full tilt until charged, not really the way an internal regulator works. A lot of the smart regulators will come with a alternator and battery temperature sensors. They reduce output if either starts to get too warm.

 

[shade]

F550 has dual alternators that have the possibility to push a lot of amps, so the only ACR I could find was the ML series from Blue Sea that are good for 500 amps. However, it seems like the ACR will not fully charge batteries because it is not a smart battery charger.

ML-ACR Automatic Charging Relay with Manual Control - 12V DC 500A - Blue Sea Systems

500 Amp magnetic latching (bi-stable) relay automatically combines batteries during charging and isolates batteries when discharging and when starting engine.

www.bluesea.com

That isn't a battery charger. Here's a good article on the subject:

Making Sense of Automatic Charging Relays - Marine How To

Making Sense of the ACR WARNING: The ACR's in this article are not for use with LiFePO4 Batteries! What is an ACR? An ACR is nothing more than a fully automatic, voltage triggered, BOTH/PARALLEL switch that closes when charging voltage is present and opens when charge

marinehowto.com

I think you're wanting to charge a 400Ah to 600Ah battery bank. If so, it will take a "small solar system" days to charge that to 100%. With dual alternators, it would also take a 20A DC-DC charger a needlessly long time to get the job done if the depth of discharge is around 50%.

With two alternators putting out considerable power, you may be able to charge your house bank directly from one of them if the load isn't too much. You could also get a higher output DC-DC charger to make the most of the alternator output for bulk charging.

 

[luthj]

First. What is the voltage of your alternator when hot? That will determine if you can get a full charge from the alternator alone.

One option is to isolate one of the alternators, and use a external regulator to turn it into a high powered battery charger. It would then be connected to the house battery bank directly.

With 400AH of flooded lead, you are not likely to exceed 150A, even when deeply discharged. The only caveat, is if your alternator voltage is in the high range (like 14.5V) then you might be able to exceed that with a big fat cable, and deeply discharged batteries. Lead batteries charge current rapidly tapers above 50% SOC. That last 2-3% of the charge will be at 2% of C.

As shade mentioned, an ACR is not a charger. Its just a voltage sensing relay. Basically a switch with some logic. It just connects the battery to the vehicles electrical system when the voltage is above a certain value. Attaching an ACR and a DC-DC would be self defeating. The ACR would just bypass the DC-DC, and you would have an expensive space heater.

 

[DiploStrat]

Scholars differ, but if you have a classic 'Murican pickup, with an alternator putting out more than 14v, charging lead acid batteries (AGM/FLA/etc.) then you probably have no need for anything other than a relay and some big cables. I ran this for years using a Chevrolet 3500 and 600Ah of AGM. As with all lead acid, the real test is the long absorb stage and, as it is unlikely that you will ever drive long enough to complete the charge, this requires solar, shore, or some other long term charger.

Battery to battery chargers offer benefits, if you need them. This is achieved at the cost of cost and a reduction in the amperage. (Which can be a benefit, see below.):

-- For lead acid, a voltage boost. This can be an issue with some Mercedes Benz and Toyotas whose alternators top out at 13.9v. (Also useful in odd cases, like my new truck, of a 24v vehicle with a 12v camper battery.)
-- For lithium, a limitation in the amperage, which can be useful as lithium batteries do not have the rising internal voltage of lead acid and tend to take the full output of the charge source until they are fully charged.)

In the instant case, as outlined in the original post, a well executed ACR installation should be ideal. Barring odd, low voltage, I would not use a B2B.

Even with a 200Ah overnight discharge and big cables, you are unlikely to see a charge rate of much over 100A for more than thirty minutes with lead acid. The internal voltage will rise rapidly and your typical, long term rate will be around 50A. (Which will have you cussin' 'cause your 400A alternator still take HOURS to charge your batteries. Is this a good time to extol the virtues of lithium? )

YMMV

N.B. The marine link above is very good. Worth noting, however, that the suggestion of connecting the alternator directly to the camper (or "house") battery, while excellent, is not usually possible on a truck, given the complexities (and warranty issues) of modern vehicle. It is the better way to do things, if you can, as the camper battery is larger and does more work than the starter battery. As a practical matter, this is not much of an issue if your wiring is large enough - typically 0AWG.

 

[john61ct]

Sorry did not read the thread

I've been scratching my head on how to charge my batteries in my F550 shuttle bus. Planned set up is 4-600 amp hours of 6v golf cart batteries.

F550 has dual alternators that have the possibility to push a lot of amps, so the only ACR I could find was the ML series from Blue Sea that are good for 500 amps. However, it seems like the ACR will not fully charge batteries because it is not a smart battery charger.

I am considering two options. One, a small solar system that has a smart battery charging profile I like built in to the controller. Or two, an additional 10 or 20 amp dc to dc charger in addition to the ACR. But I can't find anybody that's done that before.

An ACR is just an open / close relay based on charge source being present, aka VSR, combiner.

It does not have any stages, no change in voltage, no termination no Float.

If you and the bank specs are OK with that the BSS ML is the best on the market, bulletproof.

If your target bank needs a different voltage and is worth coddling to get longer lifespan, then you need a DCDC charger.

Personally I reco getting one lets you adjust your setpoints to custom values, Sterling BB series or maybe Kisae.

But most with a bank under a grand do fine with an ACR,

 

[pugslyyy]

As we are converting from AGM to LiFePO4 batteries we are swapping out the Blue Sea ACR for the Sterling 120A DC-to-DC charger. You can program it for all battery types, and it has temperature sensing for the house battery. All in all it is a more robust charging solution for any type of battery. Other companies make DC-to-DC chargers, but Sterling makes the highest capacity (that I've found).

What we do is replace the Blue Sea ACR with a 150A fuse, and then install the DC-to-DC charger in the house battery bay.

 

[john61ct]

Yes for an expensive LFP bank, DCDC for sure.

Those bigger Sterlings BBW series, require the add-on pendant to user-customize setpoints.

The BB line, max 60A input, does not.

The former are also noisier, designed to mount outside.

 

[pugslyyy]

Yes for an expensive LFP bank, DCDC for sure.

Those bigger Sterlings BBW series, require the add-on pendant to user-customize setpoints.

The BB line, max 60A input, does not.

The former are also noisier, designed to mount outside.

The controller makes programming easier, but you can also do it with just a magnet.

 

[john61ct]

Only within their canned choices

none if which I would use for LFP.

I'm talking about setting up a **custom** profile, where you tweak the Absorb or Float yourself to match the precise needs of your bank chemistry.

In lead you should follow the mfg datasheet.

With LFP definitely not, if you care about optimizing for longevity.

 

[pugslyyy]

Only within their canned choices

none if which I would use for LFP.

I'm talking about setting up a **custom** profile, where you tweak the Absorb or Float yourself to match the precise needs of your bank chemistry.

In lead you should follow the mfg datasheet.

With LFP definitely not, if you care about optimizing for longevity.

Interesting. How did you configure yours for LiFePO4 batteries? Battleborn's recommendations are in line with the built in LiFePO4 settings, and we actually buy it as a packaged system from them.

 

[john61ct]

In Battleborn's case the non-adjustable inaccessible BMS' balancing algorithm likely requires going to a higher voltage than I would ever allow, and holding it longer than is healthy.

But you can't even tell when it's finished.

Idiotic design IMO.

I do not recommend any drop in set up like that.

But sure, if a given charge source's canned profiles happen to match what you think is good for your bank chemistry, then as ling as you own that bank, you don't need a custom adjustment.

 

[pugslyyy]

In Battleborn's case the non-adjustable inaccessible BMS' balancing algorithm likely requires going to a higher voltage than I would ever allow, and holding it longer than is healthy.

But you can't even tell when it's finished.

Idiotic design IMO.

I do not recommend any drop in set up like that.

But sure, if a given charge source's canned profiles happen to match what you think is good for your bank chemistry, then as ling as you own that bank, you don't need a custom adjustment.

I only have a degree in electrical engineering and have never really done a deep dive into batteries. The founder of Battle Born has degrees in Physics (BS Villanova) and Engineering (PhD, Caltech), and is also a professor who teaches at UNR in the Physics department. Absent evidence to the contrary, I'm going to go with his judgment.

 

[john61ct]

They do seem good about honoring their very generous warranty, so as long as they stay in business, that's something good for sure.

Many people will be happy to just get ten years' use.

 

[luthj]

BBs goals are a bit different than Johns (I am not as conservative, but agree with most of his recommendations). John seems focused on targeting 15 years of life from a pack (daily cycling). When cells were much more expensive, this was a big deal. With cell prices dropping, and the quality of the cells improving, this is less of a concern.

BBs charge target of ~14.6V is fine if you stop immediately upon reaching that target. No float, and allow the bank to coast down to the mid 90s SOC under normal house loads. Sitting at that voltage for any appreciable length of time does unneeded damage to the cells. If you are only looking at 3-5 years before you replace the pack, or if you only use the pack a few months a year, you may never notice the difference if the pack is stored properly.

Personally I would be more conservative with my charge voltages, but as always there are lots of variables to consider.