Start Battery Trickle Charging

[rgleason]

I like this idea and will probably implement it.

See Sherry and Dave's "SoggyPaws" blog website on his Electrical System and

Scroll down to the bottom "Start Battery Trickle Charging"
S/V Soggy Paws - St. Francis 44 - Onboard Electrical Systems

I thought that the best feature was the automatic trickle charging of the starting battery from the house bank through a short 12 gauge wire with a diode (one way current flow) and thermal circuit breaker.

The idea is that when the house bank is being charged from any charging source the diode will keep the voltage to the starting battery about 1/2 volt below the house bank voltage, and the thermal circuit breaker will break the charging circuit off if the charging amperage get too high.

The starting battery can take up to about 15 amps if it needs it but with this system it normally just takes small float current. I've never seen more than about 2 amps going into my starting battery from the house bank.

Thanks Dave

[tkeithlu]

OK. Why does your starter battery not have a proper charging system, such as an alternator with (even a sophisticated) voltage regulator? This sounds like a backup, not a primary way of charging your starter battery, and substitutes something lower for proper charging voltage (probably 13.4 v). I can see it as a Plan B for being sure that you are not left with a flat starting battery, in which case I would also see a switch in the line, but if it became necessary I would want to know what had failed in the primary circuit. The same end could be reached with jumper cables.

[Stu Jackson]

Snake oil concept that will result in chronic undercharging of a start bank.


rg, you should really know better than that. I was surprised to see who posted this drivel.

[rgleason]

Stu, I had to laugh. I like their Battery Bank System Philosophy All Charging to House Bat, House Panel Load Selector for Bank choice

I see no reason to do anything better for the Start Battery when I rewire for LiFePo
With some solar panels to the LiFePo this battery will always be full.
For example, I still have a West Marine Gel Cell from about 14 years ago that starts the 3YM30 fine, and seldom charge it, well only occasionally, also during the winter, never above 14.1v. I keep thinking I really should get a new start battery.

Yes I know it is essential backup if the House/LiFePo shuts off, but is it really that important? For awhile I was thinking of getting one of those Lithium booster starters to save some space. This would be a little better than that.

Read SoggyPaws report, it seems to work and it is cheap and reliable. Sure it might sulfate, but I'd only have to replace it every 4 years, and I can recondition it in the winter on the 120vac 15a charger.

[Stu Jackson]

rg, so you have a 14 yr old battery that still works but you're switching to something that'll give you four years.


Is that progress, or what?!?

[rgleason]

Stu That's why I haven't changed it yet! Too cheap. When it happens maybe it should be Agm but those are expensive.

tkeith I have a balmar regulator w temps & belt manage and alt goes direct to house bat.

[stormalong]

There are at least a dozen manufacturers of automatic charging relays (aka battery combiners). They will join the batteries together anytime the voltage in either battery rises to charging levels and separate them when charging stops. Not terribly expensive.

A diode as suggested will not do the same thing. Anytime the house battery is more than .6 volts higher than the start battery current will flow. A weak start battery will constantly draw power from a stronger house bank. A parasitic load.

Don't cheap out - do it right.

[Cadence]

I see nothing wrong with the idea of a blocking diode as long as the house and starter batteries are of the same type, eg FLA , AGM or whatever and require the same degree of charge. I'd guess it is to keep the starter battery from being flat after a long layup without the cost of an independent charger. A switch in the line to interupt the connection when starting the engine would be in order and a fuse incase of forgetting to flip the switch off, you wouldn't want to smoke that 12 ga. wire.

[Mike OReilly]

Originally Posted by stormalong

There are at least a dozen manufacturers of automatic charging relays (aka battery combiners). They will join the batteries together anytime the voltage in either battery rises to charging levels and separate them when charging stops. Not terribly expensive.

A diode as suggested will not do the same thing. Anytime the house battery is more than .6 volts higher than the start battery current will flow. A weak start battery will constantly draw power from a stronger house bank. A parasitic load.

Don't cheap out - do it right.

I was just about to say, sounds like a haphazard way of setting up an ACR. Or what about an echo charger? Cheap, simple, and safer.

My charging approach is to have the alternator charge the starter bank, and have my passive chargers (solar/wind) charge the house bank. I can direct the alternator charge to the house bank via the standard 3-way switch (or can combine them), but basically I use the alternator to charge the starter battery. This ensures it is always charged after use.

[Cadence]

Originally Posted by stormalong

There are at least a dozen manufacturers of automatic charging relays (aka battery combiners). They will join the batteries together anytime the voltage in either battery rises to charging levels and separate them when charging stops. Not terribly expensive.

A diode as suggested will not do the same thing. Anytime the house battery is more than .6 volts higher than the start battery current will flow. A weak start battery will constantly draw power from a stronger house bank. A parasitic load.

Don't cheap out - do it right.

If the charger for the house is good, I don't see the problem. It is similar to having parallel batteries in a charging mode. Parasitic no.

[stormalong]

Originally Posted by Cadence

If the charger for the house is good, I don't see the problem. It is similar to having parallel batteries in a charging mode. Parasitic no.

Is the house bank continuously charged? Many are not. They are on moorings or at anchor with no solar of wind power to charge them..

No two batteries are alike. As batteries get older they self discharge faster, IOW they don't hold their charge. If the house battery is newer and in better condition it's rested voltage could be higher than an older start battery. A continuous discharge into the start battery to maintain it is a parasitic load - one that accomplishes nothing but bring down the house battery.

An ACR is a much better choice. It is only active when there is a charging source and there is no voltage drop between the two batteries.

[Cadence]

Originally Posted by stormalong

Is the house bank continuously charged? Many are not. They are on moorings or at anchor with no solar of wind power to charge them..

No two batteries are alike. As batteries get older they self discharge faster, IOW they don't hold their charge. If the house battery is newer and in better condition it's rested voltage could be higher than an older start battery. A continuous discharge into the start battery to maintain it is a parasitic load - one that accomplishes nothing but bring down the house battery.

An ACR is a much better choice. It is only active when there is a charging source and there is no voltage drop between the two batteries.

Maybe I'm assuming q charger of some type on the house bank? I don't recall any reference to battery age? Parasitic no more than a bad house bank battery.

[rgleason]

There are two different cases here. SoggyPaws case (read the link) who has LFP with lots of solar on a cat and an older battery of unknown type. It is a excellent writeup of his process, decisions and the installation itself.

Second case is our future use.
1. Mooring, no shore power, solar 100w now, maybe 300w later
2. Use 90ah/day cruising 140ah/day at sea, refrig and navigation.
3. New 160a Alt belt managed down to 100a
4. with temp sensors and Balmar Regulator or Smart Alt Reg.
5. Want faster charging on anchor and in/out harbors
6. Solar to make up difference.
6. New 200-300ah LiFePo batteries in cabin under settee
7. Simplest configuration possible.
8. Solar & Alt chargers connected to House LFP
9. Starter connected to Start Battery
10. No built in charger or inverter - carry 15a 120vac portable charger used during the winter.
11. Have very little room for new gear below.
12. Would like to have a small AC panel for ref & dhw + 2 outlets.
13. Would like to have a small inverter-charger but can't figure out where it would fit nicely.

In thinking about this more, I think I'd like to be able to use the the start battery as a spike dump for alt protection if I can't find a reasonable BMS that will automatically shut off the alternator FCC (before shutting off the LFP) or if Balmar's new spike dump won't be adequate to protect the alternator. If Balmar's new alt protection device is adequate, then maybe I don't need the starter as a spike dump and don't need the LFP to have a BMS with external controls, but BattleBorn are too expensive and won't fit under the bunk, so I need a decent BMS anyway.

All loads will be automatically shut off when LFP cuts out if I don't have a dual bus. Then start battery would have to be used for loads, while hoping the LFP problem can be resolved.

I just really liked the simplicity of the #12 wire, the diode and the thermal fuse. Right now I have nothing like that, no ACR, nothing and my battery banks are two different types. House FLA Trojan 213ah and Start West Marine Gel 14 year old about, at 80%C and its still starting.

There is too much wiring already, & gets in the way of sailing.

Yes, the use does matter.

[smac999]

the best way now is a victon Orion smart dc to dc.

[rgleason]

However I don't want to limit my charging of LFP to just 30a and having to get mulitple DC-DC as there is no room for it. It might be simple but it is not for my use. Are you saying use that for the start battery? That is overkill in my opinion, what would the advantage be?


Note

. Want faster charging on anchor and in/out harbors

Originally Posted by smac999

the best way now is a victon Orion smart dc to dc.