Powering Electronics Through Starting Voltage Drop

[Happ]

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.

The answer is simple. A Starting Battery is constructed for exactly what happens when you start the engine. It require a high output for a short time. That’s why everybody has a Starting Battery on a separate circuit.

House batteries are designed for low output for a long time. That’s why there on a separate circuit referred to as House Batteries.

[mcon12000]

I haven't read all the posts...

Remove the A/B/All Switches

Alternators connect directly to a single large house bank.

Victron 18amp DC to DC chargers top off the start batteries via the house bank.

Now you can have batteries that are optimized for their intended use vs dual purpose.

All electronics and 12v loads are fed from the house bank eliminating the voltage sag at start.

Remember that typically the start batteries will be in a very high state of charge after starting your motors. Compare that to your correctly sized house bank's 50% SOC (assuming LA) after a night on the hook and we can begin to see why it makes more sense to route all the available charging sources to the house bank. Why? Because the start batteries will be into float minutes after a start but the house bank will be in bulk for hours. This is also a strong argument against a simple ACR and a big reason why DC to DC chargers are taking over.

[mitiempo]

Originally Posted by mcon12000

......This is also a strong argument against a simple ACR and a big reason why DC to DC chargers are taking over.

DC to DC chargers make sense if the batteries are not the same type - eg fla start and LiFePo4 house bank.

If the batteries are the same type - fla, agm, or gel - there is no reason not to use an ACR.

[mcon12000]

Originally Posted by mitiempo

DC to DC chargers make sense if the batteries are not the same type - eg fla start and LiFePo4 house bank.

If the batteries are the same type - fla, agm, or gel - there is no reason not to use an ACR.

That's essentially what I'm saying and certainly not saying ACR's are bad. In the scenario I presented you could have an ACR between the starting batteries and only one DC to DC charger for both. The house bank and the starting banks "ideally" are not the same type of battery so the DC charger becomes attractive. I also left out externally regulated alternators since I assumed that the OP wasn't going to be spending $6k plus upgrading his whole setup. Every situation is different but I am pretty firm on never installing another A/B/All switch for anyone lol...

[chasfgr]

Have a separate starter battery, from my domestic bank.
Starter only needs a fairly small footprint battery and thius making sure that is never run down by leaving ancillaries on.

[mitiempo]

Originally Posted by mcon12000

The house bank and the starting banks "ideally" are not the same type of battery so the DC charger becomes attractive.

If start and house batteries are both Fla they are the same type. If they are both Agm they are the same type.

ACRs are much less expensive than DC to Dc that have charging profiles. They are also not voltage limited like Dc to Dc is.

[andrewvik]

This Blue Sea ACR will do the battery switching for you, AND isolate your house bank during engine cranking. $79.

https://shop.pkys.com/Blue-Sea-7610-...CR_p_1626.html

[Perdiem]

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.

I too have two engines, one start battery and one house bank. Both engines start off the start battery (a 4D) but the port engine charges the house bank.

I always start the starboard engine first so that the port engine is seeing 14 volts when it starts. The voltage on the house battery (which powers the electronics) never sees a voltage drop.

Either I am doing something wrong or you guys are overcomplicating this.

[rslifkin]

Originally Posted by Perdiem

I too have two engines, one start battery and one house bank. Both engines start off the start battery (a 4D) but the port engine charges the house bank.

I always start the starboard engine first so that the port engine is seeing 14 volts when it starts. The voltage on the house battery (which powers the electronics) never sees a voltage drop.

Either I am doing something wrong or you guys are overcomplicating this.

That seems like a reasonable setup to me. Only reason I made mine a bit more complicated was to allow both alternators to charge the house bank (and not lose house bank charging if I have to shut either engine down). And I like redundancy.

[m0ggy]

Originally Posted by Perdiem

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.

I too have two engines, one start battery and one house bank. Both engines start off the start battery (a 4D) but the port engine charges the house bank.

I always start the starboard engine first so that the port engine is seeing 14 volts when it starts. The voltage on the house battery (which powers the electronics) never sees a voltage drop.

Either I am doing something wrong or you guys are overcomplicating this.

Yes Yes Yes Been wiring up boats for a long time
One start battery that does nothing else but start either engine and the house bank that powers everything else. No highly complicated and expensive charge control things DC to DC chargers etc. Much cheaper and a fair bit more reliable KISS .And no switching apart from a 1 or 2 or both switch to feed the starter motor from either/or both battery banks

[Cynara]

We always turned off the electronics before starting. make it a habit then you won't forget. Like opening the engine thru-hull before starting.

[topmast]

Had two house banks and separate start Worked without problems until Dept.of Transport said radio and nav stuff needed isolated power source. ( 18 passengers) So made everything run off a separate battery (big lawn mower type) and charged dc/dc . One more volt meter to keep an eye on.

[bharney]

You need a dedicated starting battery that only starts the engine, everything else ie electronics connected to house bank. There are various devices like echo charge to keep the start battery charged but you could also just put the battery switch in "Both"
position for a while to keep it charged.

[mitiempo]

Originally Posted by Cynara

We always turned off the electronics before starting. make it a habit then you won't forget. Like opening the engine thru-hull before starting.

That works for some.

In this area there are many fishing boats that may start and stop their engines a dozen times a day. This requires a system that doesn't drop the electronics out when starting - eg a dedicated start only battery.

[mitiempo]

Originally Posted by Perdiem

I too have two engines, one start battery and one house bank. Both engines start off the start battery (a 4D) but the port engine charges the house bank.

I always start the starboard engine first so that the port engine is seeing 14 volts when it starts. The voltage on the house battery (which powers the electronics) never sees a voltage drop.

Either I am doing something wrong or you guys are overcomplicating this.

Sound like a good solution. The only thing I would add is an ACR between the banks. This would allow both alternators to charge the house bank after the start battery is full, which doesn't take very long.