Charging on/off switches - needed?

[jc1409]

I'm designing a LIFEPO4 setup that will include the following battery charging sources. I'm overthinking and over-engineering everything, and now thinking about how I can overdo things by adding more switches into the mix.

Assuming proper fusing, would you recommend that a conveniently-placed switch be added to allow on/off switching between the charger and the battery (either for convenience, safety, or functionality)?

1. Alternator charging to LIFEPO4?
- this could be dangerous if switched off while alternator running - would think clear answer is NO

2. Solar MPPT charging to LIFEPO4?
- already have breakers upstream of MPPT - would be just for convenience; have seen mixed messages about dangers of disconnecting battery from MPPT while panels connected, but tending to think would be okay

3. Shore power charging to LIFEPO4?
- would be convenience so I could easily leave LIFEPO4s in <100% state while on shore power for extended time, which I understand is better for them

4. DCDC charging from LIFEPO4 to AGM banks?
- would want to keep AGM banks topped up - don't know when I would want to switch this off, so thinking not necessary

I will already have a LIFEPO4 main battery disconnect switch (well-hidden away) to disconnect the bank fully if every needed.

Jeff

[tkeithlu]

In the case of the charger I don't see the need. It has an on-off switch already, so you don't do the battery-inverter-charger-battery perpetual motion dance. In the case of Li-ion-AGM yeah, you don'twant to equalize those two. Maybe a switch and a timer if you are as attentionally deficient as I am.

[CharlieJ]

Recommend an on/off switch in alternator output. Use for maintenance on the alternator to prevent accidental short to ground. Concerned about “somebody “ changing switch position? Use a switch with a key.

[PaulCrawhorn]

Circuit protection for wire runs maybe.

Switch should disable the source, not interrupt its output

[BMD21]

I just got through installing a Chins 100 AH Li battery in our boat. The charging is handled by a 20 amp Victron DC-DC charger. It has 2 control lines: charging and 1/2 rate charging. The charging is supposed to be connected to your alternator, or any switched source. The 1/2 rate charging command uses a 12 V command to select 1/2 rate charging. The DC-DC charger is fed from a common alternator/starting battery.


I installed 2 ea control switches so that i control the DC charger whilst I'm on shore power. When the engine is not running and the shore power is plugged in, the main battery charger will keep the starting battery charged. When I want to charge the Li battery, I just turn on the charging switch. Of course I have to remember to turn on the switch when the motor starts.


The Xantrex 20 amp battery charger apparently puts out 10 amps per battery for a total of 20 amps. So I'm glad I installed the 1/2 rate control. Whence I'm on shore power and the Li battery is feeding the house circuits, I can select 1/2 and then go to full rate when the motor is running. It all works.



Boris

[alctel]

Originally Posted by jc1409

I'm designing a LIFEPO4 setup that will include the following battery charging sources. I'm overthinking and over-engineering everything, and now thinking about how I can overdo things by adding more switches into the mix.

Assuming proper fusing, would you recommend that a conveniently-placed switch be added to allow on/off switching between the charger and the battery (either for convenience, safety, or functionality)?

1. Alternator charging to LIFEPO4?
- this could be dangerous if switched off while alternator running - would think clear answer is NO

2. Solar MPPT charging to LIFEPO4?
- already have breakers upstream of MPPT - would be just for convenience; have seen mixed messages about dangers of disconnecting battery from MPPT while panels connected, but tending to think would be okay

3. Shore power charging to LIFEPO4?
- would be convenience so I could easily leave LIFEPO4s in <100% state while on shore power for extended time, which I understand is better for them

4. DCDC charging from LIFEPO4 to AGM banks?
- would want to keep AGM banks topped up - don't know when I would want to switch this off, so thinking not necessary

I will already have a LIFEPO4 main battery disconnect switch (well-hidden away) to disconnect the bank fully if every needed.

Jeff

Yes for at least the first 3.

1) This is a definite yes, esp if you have a big alternator. If you hook the switch up to the external regulator power, you can use that to switch the alt on and off without issue even if the engine is running (this is how I set it up on my old boat)

2) Yes. I also have seen warning signs about disconnecting the MPPTs from the battery with panels on - however I never had a problem when I was doing this (I had it on my old boat set up like this). If you are worried you could buffer with the AGMs.

3) This should already be a breaker on your AC panel

4) I don't know about this one, it depends on your setup.

[CharlieJ]

I don’t think I made myself clear.

A switch in the output of the alternator, between the alternator B+ and the required OCPD where the output conductor is connected to the battery (or it’s bus) B+ is used to isolate the battery from the alternator when performing maintenance (tightening the belt). By turning the switch off while working on the alternator, the possibility of creating a violent short circuit between the B+ post and the engine block is eliminated.

[ayates]

I'm on the page of liking disconnect switches for both the AC & DC sides of chargers. This enables complete isolation for troubleshooting and maintenance.


Allan.

[jc1409]

Thanks to all. Subjective of course, but from input, summary of feedback (whether to add convenient switch to disable charging source) is as follows.



1. Alternator charging to LIFEPO4?
- Yes (good for maintenance to avoid short to grounds risks)

- Place between alternator B+ and OCPD (or maybe the switch is a circuit breaker acting as the OCPD)


2. Solar MPPT charging to LIFEPO4?
- Yes (already have upstream breakers, so only if desired for convenience)

3. Shore power charging to LIFEPO4?
- Yes (already have AC breaker (hidden away some in my setup), so only if desired for convenience)


4. DCDC charging from LIFEPO4 to AGM banks?
- Yes (convenience only)

[CharlieJ]

- Place between alternator B+ and OCPD (or maybe the switch is a circuit breaker acting as the OCPD)

Possible but not practical. Maintenance switch should be very close to the alternator. OCPD has to be very close to the B+ conductor’s attachment to the battery or its bus (7”, 40” or 72”).

[Cadence]

Just a question. Are all of the high tech. battery systems worth the complications? It would almost seem you could replace a no. of low tech. batteries without getting ulcers about your high tech. systems for a fraction of the cost. i like simple, like me, less to go bad.

[jc1409]

Good question. At least for me, I get value and enjoyment from electrical planning and tinkering, and have the time and $. Upgrading my boat setup (adding solar, replacing batteries with LFP, etc, etc) will bring me better cruising functionality and give me satisfaction in customizing boat and learning a new deep hobby.

Actually my research and planning for boat led me to setup and self-install a solar system for my home - not off grid or whole home, but its something and was fun (no idea the decades it will take to reach break-even with Michigan sun and my small setup).

[jc1409]

Originally Posted by CharlieJ

Possible but not practical. Maintenance switch should be very close to the alternator. OCPD has to be very close to the B+ conductor’s attachment to the battery or its bus (7”, 40” or 72”).

Thanks Charlie - what's the reason behind the switch being placed very close to alternator?

[tkeithlu]

General principle. When you shut something off, shut off all the wiring possible. Then a wiring short or other problem is outside the switch and doesn't affect the alternator or whatever. In this case you are talking about bunches of amps and a possible sound and light show in your engine room when the output of the alternator grounds. Same reason you put switches on the positive rather than the negative side of the circuit.

[CharlieJ]

@jc1409 #13
Simply convenience. The maintenance switch can usually be located on the engine stringer immediately under the alternator. Put a label next to it explaining its function and Bob's Your Uncle.