Battery-to-battery charger (independant of source charge voltage)

[john61ct]

The OP's been asked to clarify, hasn't come back yet.

There are plenty of use cases where loads need to get switched to a backup bank, and devices designed to do just that.

Usually it's a noticeable transition, but should be easy enough to set up an alarm light or buzzer.

As far as that last Q goes, don't know the OP's reasoning, but I've outlined my (I think reasonable) scenario above.

[knockabout]

a large buck boost regulator will take everything it can from the charge batteries (suck the guts out of them) and maintain the charged battery at 13.88 or what ever it is set for until the charge batteries drop well below 9volts at which time the low voltage buzzer squarks until the charge batteries drop below 7.5 then the buck boost regulator shuts down / buck boost regulator seems to be a type of inverter designed for 12/24volt use they will pull constant 12volt out of 24volt systems as well

[Symphony]

would seem that the wheel house emergency battery wouldn't need to have huge Ah capacity if you're running only sat phone, VHF, and GPS

[Ding Duck]

Hi Allan, this may help in the DC Charging solution.
Australian company called Redarc. Will take 9-32V DC Input and charge your Emergency batteries. Has the usual protection so as not to flatten the House battery.
https://www.redarc.com.au/dcdc-battery-charger
Has a Ignition switch input, but just bridge this out to keep output on.
As the Radios and Nav gear is connected to the Emergency battery, loosing the house battery won't make any difference to these loads as they are already connect.
Hope this helps

[skipmac]

Originally Posted by Scot McPherson

Of course you can, the electrical component that does this is called a transformer which is two sets of coils that are intertwined but insulated from one another. You can buy or make them to step up/down voltage by any ratio you want. If you need it to be variable (i.e. you need 13.6-13.8 volts no matter what the source charge is, the transformer just need a connector that slides up or down the coils until the output is at the desired voltage.

Now, the WATTS won't change (except for a little bit of loss to heat), but as the volts go up, the amps will go down, and as the volts go down the amps will go up.

Problem is the OP is asking about DC and transformers only work on AC or possibly pulsating DC but not at all on regular DC.

[ayates]

Thank you everybody for your detailed feedback and suggestions. With respect to the specific questions and points raised...

Originally Posted by john61ct

Key point missing here: how big amperage you looking for? <snip> Tell me, if you're charging every day, why aren't you just charging both banks at the same time? And what batteries are in your two banks?.

House bank: 740 AH, flooded lead acid
Emergency bank: 70 AH, sealed lead acid AGM (two of the attached photo)

The current architecture, which may not be the best solution, has the life safety loads (GPS/radios/navigation/radar/etc) tied directly to the emergency bank. If this bank was not continuously charged, I suspect it would be flattened inside a day.

Originally Posted by Pete7

Does the engine / genny charging go to the house bank and the Hopkins is powered from what?

All charging (engine/generator/shore) goes to the house bank, and the Hopkins (Engagerâ„¢ SM Break-Away System w/ Battery meter (retail box pkg)) gets its power from the house bank and charges the emergency bank.

Originally Posted by noelex 77

The Mastervolt Magic series will act as a 12v battery to 12v battery charger in the way you require.

Given the current architecture, I believe this would be exactly what I was looking for. Whether the current architecture is the best is a different matter.

Originally Posted by Ding Duck

Hi Allan, this may help in the DC Charging solution. Australian company called Redarc.

This too would do the trick nicely.

Originally Posted by Colin A

More work, but on work boat systems they will sometimes run two feeds to the helm, one from the pilothouse battery (or converter on larger ships) and the other from the main battery bank, they will either have a manual change over or a schottky diode set up to prevent back charging. You could use a system like that plus a power conditioner. This will end up being more hardware plus if you use the diodes you will have some voltage loss. But it would be a fairly robust system.

I personally tend to like the sound of this better. I always like to avoid diode losses, or continuous relay coil losses, but but both of those are probably less than the inefficiency of a DC-to-DC charger.

I am not convinced that the Hopkins charger keeps up if the radar and the other electronics are all energised. A small computer for maps/etc is being added this year, which would increase this load.

Originally Posted by Dave22q

I fail to understand your problem. Many chargers are available that will keep both banks charged. if you can charge one bank daily why not charge both? As to a seamless cutover to the 'emergency bank', sounds dangerous to me. If I'm forced to emergency power I want to know it. I think many monitors coupled with an alarm can tell you your house bank is low so you can manually switch to your back up. Why would you want the inefficiency of moving power from one battery to another?

I tend to agree. I too like in-you-face indication of failure modes. Though I do like automatic switch over in failure modes where possible.

Based on all the feedback so, I am tending towards one of:

1. Feed house bank and emergency bank through a diode combiner (e.g. https://www.victronenergy.com/batter...tery-combiners) to the critical loads.
2. Critical loads connected through a relay to the house bank, if the house bank drops off, then the relay drops the loads to the emergency bank. Manual switch to emergency bank available as well.

In both cases, both banks would be charged daily, using with a two bank charger, separate chargers, or a dc-to-dc charger (enabled when house bank has charging voltage present). In both cases, there should be visual (and audible) indication that the house bank has been lost.


Thanks,

Allan.

[ayates]

Here is the schematic of the first installation. I realise the emergency batteries are not wired ideally, but that could not be rectified at the time. Rectifying this, along with add charging redundancy and management capabilities and instrumentation are on the to do list.


Allan.

[smac999]

14awg and 10awg wire is awefully small for a panel feed

all the wires should be fused at the battery as well.

[ayates]

Originally Posted by smac999

14awg and 10awg wire is awefully small for a panel feed.

The "panel" is just six circuits and is only the critical equipment such a radio, radar, and thus only has a maximum current consumption of 6-10A.


Allan.

[ayates]

For reference, attached is the updated schematic with the "productised" layout. It now includes appropriate cabling, fusing, monitoring, and logging.


Allan.

[RaymondR]

Originally Posted by clownfishsydney

Nothing is going to "take 12v and boost it to 13.8v".

Might a MPPT solar regulator wired between the batteries serve the functions you require?

[atoll]

i found this mfg when looking at dc-dc chargers,very reasonably priced aprox £90 and a much lower output than others like the sterling range if you only want a trickle charge with a max output of 12A


https://www.alfatronix.com/dc-dc-battery-chargers

[john61ct]

Originally Posted by RaymondR

Might a MPPT solar regulator wired between the batteries serve the functions you require?

No, at least not alone afaik all need an input voltage quite a bit higher than the target output.

Optimate TM-500 does this but only a 2A maintainer "trickle" charge.

[john61ct]

Originally Posted by atoll

i found this mfg when looking at dc-dc chargers,very reasonably priced aprox £90 and a much lower output than others like the sterling range if you only want a trickle charge with a max output of 12A


https://www.alfatronix.com/dc-dc-battery-chargers

> ensure that they will not operate unless the source battery is*attached to a charging source such as a vehicle alternator or mains unit. In this way,*you can ensure that the charger will not allow unintentional draining of the source*battery

I believe this thread is about devices that do allow the target batt to charge off source even when no upstream charge source is active.

[btrayfors]

Allan,

I think you're making this way too complicated and expensive and prone to unwanted reliability risks.

Here's why:

1. Your "emergency" battery bank is WAY, WAY too small @ 70AH. Replace the two little AGMs with, e.g., two golf cart batteries which will TRIPLE the available capacity (e.g., 220 AH);

2. Use flooded GCs, just like your main "house" battery bank; don't mix chemistries;

3. Use either a combiner or, better IMHO, a voltage follower device like the Xantrex EchoCharge or Balmar DuoCharge to automatically maintain the "emergency" bank. No switching needed.

4. Forget about connecting both banks to a battery charger or other charging source: the combiner/voltage follower device does that automatically.

5. Run ALL charging devices to the house bank only.

6. Rename that "emergency" bank to something else, since it isn't an emergency bank at all. It powers several critical things, including your VHF radios.

7. Do a test to find out what the daily AH draw really is on that bank. Then, you'll know how much AH capacity you really need, given your cruising patterns.

8. Lose the diode devices...all of them. Not needed and a complicating factor.

9. Implement the above. Very easy. Inexpensive. Try it for awhile. If it turns out you need a larger capacity for the wheelhouse bank, just add a couple of golf-cart batteries to double your capicity.

10. If you don't have room for these batteries, make room. Be creative.

Good luck,

Bill