Powering Electronics Through Starting Voltage Drop

[mitiempo]

Originally Posted by Dockhead

Certainly that's one way to do it.


However, I have seen more alternators destroyed and banks inadvertently run down by those infernal 1-2-both-off switches than I can shake a stick at. I wouldn't have one on my boat.

The way I wire boats that is impossible. All charge sources including alternators go directly to a battery bank.

I also dislike 1/2/both/off switches. My preference is a simple on/off for start and another on/off for house loads. Labelled properly. Very easy for anybody to understand. A third on/off switch can be in a less convenient place to start the engine from the house bank or power house loads from the start battery if it ever comes to that.

Never combine a dead battery with a good battery. If the start battery is dead the switch should be wired so you can start from the house bank alone.

[mitiempo]

Originally Posted by rslifkin

Charging, etc. is all designed to account for this (inverter and solar charge the house bank, separate 3 bank charger for the start batteries, and the ACRs to charge the house while the engines are running).

With the ACRs - assuming they are reasonably modern - the start batteries are also charged by solar and the inverter. Popular ACRs are dual sensing - Blue Seas and Victron for example.

[mitiempo]

Originally Posted by Dockhead

That makes sense. My experience is with the switches being used in normal operation, so subject to operator error with resulting destruction.



If you want to protect the alternators from someone accidentally flipping the switch while the enginers are running, I would suggest using one of the Sterling alternator protectors, rather than field cutoff. AFAIK, cutting field will not be fast enough.

Or wire the alts directly to the batteries so they can never be damaged.

[rslifkin]

Originally Posted by mitiempo

With the ACRs - assuming they are reasonably modern - the start batteries are also charged by solar and the inverter. Popular ACRs are dual sensing - Blue Seas and Victron for example.

I intentionally used ACRs with a disable wire (the marinco/BEP ones) and connected them to the engine ignitions. That way they're out of the picture with the engines off to allow independent charging and to be sure they disconnect immediately on engine shutdown, leaving the engine batteries topped off.

[Bawlmer]

I switch everything off at the panel before starting the engine. After the engine is running you turn them on again. Once you get used to the process it really isn't an issue.

[David B]

Originally Posted by CaptTom

Just wondering what others do about maintaining voltage to various electronic devices during engine start, when the voltage can drop below whatever minimum sustains the device, causing it to fail and restart.

I've seen this with chartplotters, radios and other helm electronics. I currently have this problem with my inverter/charger control panel. Looking ahead, I'd like to add more "smart" devices such as a Raspberry Pi and no doubt these will have the same problem.

I can think of a few workarounds, but wanted to hear what others are doing before I go down an unnecessarily complicated path.

The simplest option, running all electronic systems off the house bank and having a dedicated starting bank, isn't ideal for me because I have two engines, one set to start off (and charge) each bank. It's not convenient to go down into the engine room and manipulate the switches before and after each engine start.

From my perspective, I see no issue with arranging so that you have a start battery for each engine (and therefore full redundancy). Then via splitters, those engines charge your service bank - which is the only way electronics should be supplied.

[ranger58sb]

Originally Posted by ranger42c

It's also common to have a parallel switch at the helm... so if one engine won't start due to low battery, the switch will momentarily add the battery from the other engine.

Often, these are two-way rocker switches so pressing ON in one direction engages one of the two batteries as the primary, ON in the other direction engages the other battery as primary. So one way or the other, there's enough juice in the "primary" battery to activate the parallel solenoid.

Ummm.... it only just now occurred to me that using the parallel switch when starting an engine -- when the electronics are already on -- might solve the voltage drop issue in the first place.

If so... Duh! Wish I'd thought of that earlier.

If not... OK, back to the regularly scheduled discussion.

-Chris

[CaptTom]

Wow, thanks everyone for all the thoughtful replies!

I guess battery configuration is right up there with anchor selection for strong opinions.

And, you've all helped me settle on an idea. I keep coming back to this thought:

Originally Posted by Lake-Effect

The answer is isolation in some form: if not separate start batteries, then maybe a separate battery to power the electronics you want to hold up.

I have just the spot for a small bank; anything from a motorcycle starting battery to two golf cart batteries. It's right below my 12V breaker panel. Low but not in the bilges. I'd run just the critical electronic loads off this bank.

Originally Posted by oleman

The simplest solution is a buck-boast DC-DC Inverter for a few hundred watts of isolated power to run the emergency systems.

The geek in me likes this solution, too. I just don't feel like doing the research needed to design a system which can keep the desired loads at the needed voltages given the actual voltage drop, which I also would have to research.

Originally Posted by Squanderbucks

I have a Newmar StartGuard.

Now we're getting somewhere! This is exactly what I need. All in a rugged form factor with all the engineering already done. But at that price point (I found them around $200 and up) I think I can do better.

Originally Posted by ranger42c

Ummm.... it only just now occurred to me that using the parallel switch when starting an engine -- when the electronics are already on -- might solve the voltage drop issue in the first place.

I actually have one of these I could wire up to do exactly that, and probably will, just to make emergency starting easier. But my gut tells me it won't solve the voltage drop problem at the far end of some of my 12V wire runs.

Which leaves me with adding a new battery bank. All I have to do keep it isolated except when charging. An ACR will do that, for $100 and up.

But I don't really need anything that complicated. A few minutes with my search engine of choice led me to the term "VSR," or voltage sensitive relay. One AliExpress listing had all the search terms right in the title "12V 140A Voltage Sensitive Split Charge Relay VSR for Camper Car Smart Battery Isolator Charge 2 Battery Bank Auto Parts." For around $20.

Now we're getting into my price range. For $20 more than the StartGuard, I can have two Costco golf cart batteries AND a way to charge them when the voltage gets above 13.3V. This gives me the added benefit of a robust, isolated electrical system which will automatically power my critical electronics in an emergency, something I've always wanted anyway.

[Shrew]

My starting battery is way oversized and I don't have this issue. I used to have this issue on my previous boat, and got into the habit of starting the boat first and the electronics second.

Since the OP is running a power boat.....I would wire the electronics to the house bank, then install an ACR to have the alternator push charge to both.

[Dockhead]

Originally Posted by Bawlmer

I switch everything off at the panel before starting the engine. After the engine is running you turn them on again. Once you get used to the process it really isn't an issue.

Might be ok on a motorboat. But that would be a potentially dangerous PITA on a sailboat where you might be underway when you start the engine.

[ranger58sb]

Originally Posted by Dockhead

Might be ok on a motorboat. But that would be a potentially dangerous PITA on a sailboat where you might be underway when you start the engine.

And OP has a powerboat.

-Chris

[rslifkin]

On a powerboat, the electronics power cycle isn't necessarily dangerous, but it's still annoying. If I stop in for a pumpout or something where I'm going to shut the engines down for 10 minutes, it's annoying to need to re-cycle the electronics, rather than just starting up the still-warm engines, giving them 30 seconds and being ready to go.

[CaptTom]

I really appreciate all the good ideas and strongly-held opinions here. Hearing different solutions is exactly why I posted. And I hate to contribute to thread drift on my own thread, but...

I have been in situations where rebooting all the electronics was downright dangerous. Here is just one possible scenario: You hear another boat or waves crashing on shore in the fog and shut down your engines to listen. That's not a good time to be fiddling with controls on your radar, then waiting for its 60-second start-up delay.

Another issue for me is that my battery monitor maintains a running total of current drawn from the house bank. When it reboots due to low voltage, that number is lost. So if I'm anchored for a while, then start the engines, I have to wait until I'm back to 100% SOC before I can trust the gauge again.

As to why I start each engine off a different bank, it's the KISS principle. One bank for each alternator, with appropriately sized wire, feels safest to me. I never have to manipulated switches (although in a pinch, I can.) My higher-capacity alternator feeds the house bank directly, no other points of failure along the way. No need to find a place for a second starting bank and all the associate wiring and switching. I already have a dedicated genset starting bank and even a pair of jumper cables, so all the redundancy I need.

[rslifkin]

If you already have a genset start bank, then consider reconfiguring so the genset shares with 1 engine while the other engine has its own start bank. Genset and engine sharing doesn't present any issues and it would keep the 2 engines on separate start banks (and avoid starting from the house).

[Bluechart]

Originally Posted by bcboomer

Check out the Blue Sea ACR wiring diagrams. I'm pretty sure there is a solution using them as they have a built in isolation circuit and can be manually controlled.

Isolation is the key! The ACR system is easy and one of the best.
Will allow you to start your engine at any time, even if house bank is fully discharged.

You I’ll not shutdown your navigation equipment with voltage sags,

AND, ACR prevents the starter spikes, which can fry your navigation equipment.
“ Engine starting causes voltage sags and spikes in the starting circuit.”