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Peter(at)sportingaero.com
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 Posted: Mon Dec 23, 2019 3:23 pm Post subject: Single alternator architecture |
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Does anyone have any experience of using a small 1Ah battery as a brown-out booster?
In my last aircraft I implemented an endurance bus with the main bus divided in half by a large diode. The electrical system was constructed to provide around an hours’ flying time in IMC after alternator failure. When my alternator quit 1000 miles from home I flew (VFR) for 6.5 hours and 3 engine starts on the battery, although the 3rd engine start (after 6 hours) was a little sluggish. My conclusion was the endurance bus was somewhat redundant as I load shed more aggressively than the endurance bus did. I guess an alternative conclusion is that I put too much on the endurance bus. If I did not have an e-bus I would retain the switch to connect the battery directly to the busbar (shedding the main contactor after engine start) as it also allows the field current to be switched off with the master (no separate alternator switch).
When operating normally there was no brown out during start as the EFIS had an internal battery, but I did wait until after start-up to switch on the GPS. I had considered including a small lead-acid battery to keep all the avionics on-line during starting but never did as I flew IFR only occasionally.
I have now just bought a new (to me) aircraft that suffers from brown out during starting. The architecture is a little curious in that it has an Exp Bus 2 (ugh) and routes power to the engine monitor (VM-1000) through the ‘Avionics’ switch. As soon as the starter button is pressed the VM1000 quits, which is not ideal. I’m once again thinking about a small 1Ah lead-acid as an anti brown-out measure, for example an LC-R121R3PG. These batteries weigh around 1.3 lb, will give three amps for around 10 minutes and are relatively inexpensive. I also have several available each year as they are removed from DA42s my company maintains.
Once I have moved to a c/b based system is there much of a downside to using a small battery as a brown-out booster (and changing it out every year)? It would probably be connected along the lines of Z-35. This is to hold up the VM1000 and also a modern GPS – such as a GPS175 – once installed. Can anyone point to an inexpensive “brown-out booster” that I could use instead of a battery?
Regards, Peter
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ceengland7(at)gmail.com
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| Posted: Mon Dec 23, 2019 3:50 pm Post subject: Single alternator architecture |
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On 12/23/2019 5:21 PM, Peter Pengilly wrote:
| Quote: | <![endif]--> <![endif]-->
Does anyone have any experience of using a small 1Ah battery as a brown-out booster?
In my last aircraft I implemented an endurance bus with the main bus divided in half by a large diode. The electrical system was constructed to provide around an hours’ flying time in IMC after alternator failure. When my alternator quit 1000 miles from home I flew (VFR) for 6.5 hours and 3 engine starts on the battery, although the 3rd engine start (after 6 hours) was a little sluggish. My conclusion was the endurance bus was somewhat redundant as I load shed more aggressively than the endurance bus did. I guess an alternative conclusion is that I put too much on the endurance bus. If I did not have an e-bus I would retain the switch to connect the battery directly to the busbar (shedding the main contactor after engine start) as it also allows the field current to be switched off with the master (no separate alternator switch).
When operating normally there was no brown out during start as the EFIS had an internal battery, but I did wait until after start-up to switch on the GPS. I had considered including a small lead-acid battery to keep all the avionics on-line during starting but never did as I flew IFR only occasionally.
I have now just bought a new (to me) aircraft that suffers from brown out during starting. The architecture is a little curious in that it has an Exp Bus 2 (ugh) and routes power to the engine monitor (VM-1000) through the ‘Avionics’ switch. As soon as the starter button is pressed the VM1000 quits, which is not ideal. I’m once again thinking about a small 1Ah lead-acid as an anti brown-out measure, for example an LC-R121R3PG. These batteries weigh around 1.3 lb, will give three amps for around 10 minutes and are relatively inexpensive. I also have several available each year as they are removed from DA42s my company maintains.
Once I have moved to a c/b based system is there much of a downside to using a small battery as a brown-out booster (and changing it out every year)? It would probably be connected along the lines of Z-35. This is to hold up the VM1000 and also a modern GPS – such as a GPS175 – once installed. Can anyone point to an inexpensive “brown-out booster” that I could use instead of a battery?
Regards, Peter
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I've long considered (but never implemented) a system using an equivalent of the 'brownout booster' switching power supply being currently discussed, but feeding its output to a small/medium battery which would then power the 'essential' avionics (an E-bus). The switcher would be adjusted to output typical alternator voltage; 14-14.5V, or the upper edge of whatever is recommended as a safe 'float' voltage for the chosen battery. Avionics would then be isolated from ship's power and be backed up by the battery.
When I 1st started contemplating this, the power supplies were prohibitively expensive, but now that they practically pay you to take them off their hands....
Charlie
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